refactor!: invert repo directory structure

now is language first

83 files changed, 3272 insertions, 0 deletions

diff --git a/ocaml/.editorconfig b/ocaml/.editorconfig
new file mode 100644
index 0000000..64b41ca
--- /dev/null
+++ b/ocaml/.editorconfig
@@ -0,0 +1,27 @@
+root = true
+
+[*]
+charset = utf-8
+end_of_line = lf
+insert_final_newline = true
+trim_trailing_whitespace = true
+indent_style = space
+
+[*.{ml,mli}]
+indent_style = space
+indent_size = 2
+tab_width = 2
+
+[*.{opam,dune,install,sexp,conf,in}]
+indent_style = space
+indent_size = 4
+
+[*.{md}]
+indent_style = tab
+trim_trailing_whitespace = true
+
+[*.{nix}]
+indent_style = space
+indent_size = 2
+insert_final_newline = false
+trim_trailing_whitespace = true
diff --git a/ocaml/.env.template b/ocaml/.env.template
new file mode 100644
index 0000000..3adee3e
--- /dev/null
+++ b/ocaml/.env.template
@@ -0,0 +1 @@
+LOG_LEVEL=debug
diff --git a/ocaml/.envrc b/ocaml/.envrc
new file mode 100644
index 0000000..cf8df4b
--- /dev/null
+++ b/ocaml/.envrc
@@ -0,0 +1,3 @@
+dotenv
+
+use flake
diff --git a/ocaml/.gitattributes b/ocaml/.gitattributes
new file mode 100644
index 0000000..1bc2e72
--- /dev/null
+++ b/ocaml/.gitattributes
@@ -0,0 +1,7 @@
+# http://git-scm.com/docs/gitattributes#_end_of_line_conversion
+*  text=auto
+.* text eol=lf
+
+flake.lock             linguist-generated
+ocaml_template.install linguist-generated
+ocaml_template.opam    linguist-generated
diff --git a/ocaml/.gitignore b/ocaml/.gitignore
new file mode 100644
index 0000000..5456007
--- /dev/null
+++ b/ocaml/.gitignore
@@ -0,0 +1,45 @@
+*.annot
+*.cmo
+*.cma
+*.cmi
+*.a
+*.o
+*.cmx
+*.cmxs
+*.cmxa
+
+# Files containing detailed information about the compilation (generated
+# by `ocamlc`/`ocamlopt` when invoked using the option `-bin-annot`).
+# These files are typically useful for code inspection tools
+# (e.g. Merlin).
+*.cmt
+*.cmti
+
+# ocamlbuild and Dune default working directory
+_build/
+
+# ocamlbuild targets
+*.byte
+*.native
+
+# oasis generated files
+setup.data
+setup.log
+
+# Merlin configuring file for Vim and Emacs
+.merlin
+
+# Dune generated files
+*.install
+
+# Local OPAM switch
+_opam/
+
+# DirEnv cache
+.direnv/
+
+# Environment variables
+*.env
+
+# Taskfile cache
+.task/
diff --git a/ocaml/.ocamlformat b/ocaml/.ocamlformat
new file mode 100644
index 0000000..6fdcd22
--- /dev/null
+++ b/ocaml/.ocamlformat
@@ -0,0 +1,3 @@
+profile = ocamlformat
+version = 0.28.1
+
diff --git a/ocaml/CODEOWNERS b/ocaml/CODEOWNERS
new file mode 100644
index 0000000..66c50a2
--- /dev/null
+++ b/ocaml/CODEOWNERS
@@ -0,0 +1 @@
+* @djoleary
diff --git a/ocaml/CONTRIBUTING.md b/ocaml/CONTRIBUTING.md
new file mode 100644
index 0000000..832b94b
--- /dev/null
+++ b/ocaml/CONTRIBUTING.md
@@ -0,0 +1,5 @@
+# Contributing
+
+## Commit Messages
+
+We use conventional commits for all commit messages. See <https://www.conventionalcommits.org/en/v1.0.0/>
diff --git a/ocaml/LICENSE b/ocaml/LICENSE
new file mode 100644
index 0000000..1e9858b
--- /dev/null
+++ b/ocaml/LICENSE
@@ -0,0 +1,25 @@
+This is free and unencumbered software released into the public domain.
+
+Anyone is free to copy, modify, publish, use, compile, sell, or
+distribute this software, either in source code form or as a compiled
+binary, for any purpose, commercial or non-commercial, and by any
+means.
+
+In jurisdictions that recognize copyright laws, the author or authors
+of this software dedicate any and all copyright interest in the
+software to the public domain. We make this dedication for the benefit
+of the public at large and to the detriment of our heirs and
+successors. We intend this dedication to be an overt act of
+relinquishment in perpetuity of all present and future rights to this
+software under copyright law.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR
+OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
+ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+OTHER DEALINGS IN THE SOFTWARE.
+
+For more information, please refer to <https://unlicense.org>
+
diff --git a/ocaml/README.md b/ocaml/README.md
new file mode 100644
index 0000000..772c76b
--- /dev/null
+++ b/ocaml/README.md
@@ -0,0 +1,54 @@
+# OCaml Template
+
+This is a template for OCaml projects.
+
+## Quick Start
+
+1. Fork this repository
+2. Rename the repository to your project name
+3. Replace all instances of `advent_of_code` with your project name, both in files and filenames themselves.
+
+## Project Structure
+
+```txt
+.
+├── _build                  # build outputs
+├── bin                     # program entry points
+├── docs                    # documentation
+├── lib                     # public modules
+├── test                    # tests
+├── .editorconfig
+├── .envrc
+├── .gitignore
+├── .ocamlformat            # ocamlformat configuration
+├── CODEOWNERS
+├── CONTRIBUTING.md
+├── LICENSE
+├── README.md
+├── Taskfile.yml            # task runner configuration similar to make
+├── dune-project	        # dune project configuration
+├── flake.lock
+├── flake.nix               # nix flake configuration
+├── advent_of_code.install  # autogenerated install script
+└── advent_of_code.opam     # autogenerated project description
+```
+
+## Tools
+
+- [task](https://taskfile.dev/)
+- [dune](https://dune.build/)
+- [opam](https://opam.ocaml.org/)
+- [ocamlformat](https://ocaml.org/p/ocamlformat/latest/doc/index.html)
+- [odoc](https://ocaml.github.io/odoc/odoc/index.html)
+- [alchotest](https://github.com/mirage/alcotest)
+- [bisect_ppx](https://github.com/aantron/bisect_ppx)
+- [ocaml-lsp](https://github.com/ocaml/ocaml-lsp)
+- [earlybird](https://github.com/ocaml-lsp/earlybird)
+- [findlib](https://github.com/ocaml/ocamlfind)
+- [re2](https://github.com/janestreet/re2)
+- [fmt](https://erratique.ch/software/fmt)
+- [cmdliner](https://erratique.ch/software/cmdliner)
+
+## License
+
+This project is licensed under the [Unlicense](https://unlicense.org/).
diff --git a/ocaml/Taskfile.yaml b/ocaml/Taskfile.yaml
new file mode 100644
index 0000000..4a4cbe2
--- /dev/null
+++ b/ocaml/Taskfile.yaml
@@ -0,0 +1,103 @@
+# https://taskfile.dev
+version: "3"
+
+tasks:
+
+  default:
+    desc: Prints this message
+    cmds:
+      - cmd: task --list-all
+
+  docs:
+    desc: Builds documentation
+    preconditions:
+      - command -v ocamldoc
+    cmds:
+      - cmd: ocamldoc -html -d docs bin/main.ml
+    silent: true
+
+  test:
+    desc: Runs the tests
+    preconditions:
+      - command -v dune
+    deps:
+      - task: build
+    cmds:
+      - cmd: dune runtest {{.CLI_ARGS}}
+
+  test:watch:
+    desc: Continuously runs the tests
+    ignore_error: true
+    sources:
+      - lib/**/*.ml
+      - test/**/*.ml
+    preconditions:
+      - command -v dune
+    deps:
+      - task: build
+    cmds:
+      - cmd: dune runtest --watch {{.CLI_ARGS}}
+
+  test:coverage:
+    desc: Runs the tests and reports coverage
+    preconditions:
+      - command -v dune
+      - command -v bisect-ppx-report
+    deps:
+      - task: build
+    cmds:
+      - cmd: rm --recursive --force _coverage
+      - cmd: rm --force _build/default/test/bisect*.coverage
+      - cmd: dune runtest --instrument-with bisect_ppx --force {{.CLI_ARGS}}
+      - cmd: bisect-ppx-report html
+
+  test:suite:
+    desc: Run a singluar test suite, e.g. `task test:suite SUITE=test/domain/d01p01`
+    preconditions:
+      - command -v dune
+    deps:
+      - task: build
+    requires:
+      vars:
+        - SUITE
+    cmds:
+      - cmd: dune exec {{.SUITE}}.exe -- {{.CLI_ARGS}}
+
+  build:
+    desc: Builds the project
+    preconditions:
+      - command -v dune
+    cmds:
+      - cmd: dune build
+
+  build:watch:
+    desc: Builds the project when files change
+    preconditions:
+      - command -v dune
+    cmds:
+      - cmd: dune build --watch {{.CLI_ARGS}}
+
+  build:release:
+    desc: Builds a release version the project
+    preconditions:
+      - command -v dune
+    cmds:
+      - cmd: dune build --release
+
+  run:
+    desc: Runs the project
+    preconditions:
+      - command -v dune
+    deps:
+      - task: build
+    cmds:
+      - cmd: dune exec -- ./bin/main.exe {{.CLI_ARGS}}
+
+  repl:
+    desc: Opens a REPL for the project
+    interactive: true
+    preconditions:
+      - command -v dune
+      - command -v utop
+    cmds:
+      - cmd: dune utop
diff --git a/ocaml/advent_of_code.opam b/ocaml/advent_of_code.opam
new file mode 100644
index 0000000..103f2ce
--- /dev/null
+++ b/ocaml/advent_of_code.opam
@@ -0,0 +1,42 @@
+# This file is generated by dune, edit dune-project instead
+opam-version: "2.0"
+synopsis: "advent of code solutions for 2025"
+description:
+  "project aiming to solve the advent of code puzzles released for 2025"
+maintainer: ["DJ O'Leary <dijitol@proton.me>"]
+authors: ["DJ O'Leary <dijitol@proton.me>"]
+license: "Unlicense"
+tags: ["Advent of Code"]
+homepage: "https://github.com/djoleary/advent_of_code"
+doc: "https://github.com/djoleary/advent_of_code/2025/ocaml/docs/index.html"
+bug-reports: "https://github.com/djoleary/advent_of_code/issues"
+depends: [
+  "dune" {>= "3.20"}
+  "ocaml" {>= "5.2"}
+  "ppx_deriving" {build}
+  "alcotest" {with-test}
+  "qcheck" {with-test}
+  "bisect_ppx" {with-test}
+  "ppx_inline_test" {with-test}
+  "ppx_expect" {with-test}
+  "odoc" {with-doc}
+  "cmdliner"
+  "fmt"
+  "re2"
+]
+build: [
+  ["dune" "subst"] {dev}
+  [
+    "dune"
+    "build"
+    "-p"
+    name
+    "-j"
+    jobs
+    "@install"
+    "@runtest" {with-test}
+    "@doc" {with-doc}
+  ]
+]
+dev-repo: "git+https://github.com/djoleary/advent_of_code.git"
+x-maintenance-intent: ["(latest)"]
diff --git a/ocaml/bin/dune b/ocaml/bin/dune
new file mode 100644
index 0000000..0f6768d
--- /dev/null
+++ b/ocaml/bin/dune
@@ -0,0 +1,11 @@
+(executable
+ (public_name advent_of_code)
+ (name main)
+ (libraries
+   domain
+   application
+   infrastructure
+   presentation
+   logs
+   logs.fmt)
+ (modes byte exe))
diff --git a/ocaml/bin/main.ml b/ocaml/bin/main.ml
new file mode 100644
index 0000000..cbfe6d2
--- /dev/null
+++ b/ocaml/bin/main.ml
@@ -0,0 +1,16 @@
+let env_log_level =
+  match Sys.getenv_opt "LOG_LEVEL" with
+  | None ->
+      Some Logs.Warning
+  | Some lvl -> (
+    match Logs.level_of_string lvl with Error _ -> None | Ok v -> v )
+
+let main () =
+  let log_level = env_log_level in
+  Logs.set_level log_level ;
+  Logs.set_reporter (Logs_fmt.reporter ()) ;
+  Logs.info (fun m ->
+      m "Started application with LOG_LEVEL=%s" (Logs.level_to_string log_level) ) ;
+  Presentation.Cli.run ()
+
+let () = if !Sys.interactive then () else exit (main ())
diff --git a/ocaml/docs/Main.html b/ocaml/docs/Main.html
new file mode 100644
index 0000000..11d7257
--- /dev/null
+++ b/ocaml/docs/Main.html
@@ -0,0 +1,18 @@
+<!DOCTYPE html>
+<html>
+<head>
+<link rel="stylesheet" href="style.css" type="text/css">
+<meta content="text/html; charset=iso-8859-1" http-equiv="Content-Type">
+<meta name="viewport" content="width=device-width, initial-scale=1">
+<link rel="Start" href="index.html">
+<link rel="Up" href="index.html">
+<link title="Index of modules" rel=Appendix href="index_modules.html">
+<link title="Main" rel="Chapter" href="Main.html"><title>Main</title>
+</head>
+<body>
+<div class="navbar">&nbsp;<a class="up" href="index.html" title="Index">Up</a>
+&nbsp;</div>
+<h1>Module <a href="type_Main.html">Main</a></h1>
+
+<pre><span id="MODULEMain"><span class="keyword">module</span> Main</span>: <code class="code">sig</code> <a href="Main.html">..</a> <code class="code">end</code></pre><hr width="100%">
+</body></html>
diff --git a/ocaml/docs/index.html b/ocaml/docs/index.html
new file mode 100644
index 0000000..f536f1a
--- /dev/null
+++ b/ocaml/docs/index.html
@@ -0,0 +1,22 @@
+<!DOCTYPE html>
+<html>
+<head>
+<link rel="stylesheet" href="style.css" type="text/css">
+<meta content="text/html; charset=iso-8859-1" http-equiv="Content-Type">
+<meta name="viewport" content="width=device-width, initial-scale=1">
+<link rel="Start" href="index.html">
+<link title="Index of modules" rel=Appendix href="index_modules.html">
+<link title="Main" rel="Chapter" href="Main.html"><title></title>
+</head>
+<body>
+<div class = "index-list">
+<ul class="indexlist">
+<li><a href="index_modules.html">Index of modules</a></li>
+</ul>
+</div>
+
+<table class="indextable module-list">
+<tr><td class="module"><a href="Main.html">Main</a></td><td></td></tr>
+</table>
+</body>
+</html>
diff --git a/ocaml/docs/index_attributes.html b/ocaml/docs/index_attributes.html
new file mode 100644
index 0000000..3450f40
--- /dev/null
+++ b/ocaml/docs/index_attributes.html
@@ -0,0 +1,17 @@
+<html>
+<head>
+<link rel="stylesheet" href="style.css" type="text/css">
+<meta content="text/html; charset=iso-8859-1" http-equiv="Content-Type">
+<meta name="viewport" content="width=device-width, initial-scale=1">
+<link rel="Start" href="index.html">
+<link title="Index of modules" rel=Appendix href="index_modules.html">
+<link title="Main" rel="Chapter" href="Main.html"><title>Index of class attributes</title>
+</head>
+<body>
+<div class="navbar">&nbsp;<a class="up" href="index.html" title="Index">Up</a>
+&nbsp;</div>
+<h1>Index of class attributes</h1>
+<table>
+</table>
+</body>
+</html>
diff --git a/ocaml/docs/index_class_types.html b/ocaml/docs/index_class_types.html
new file mode 100644
index 0000000..be3ecc7
--- /dev/null
+++ b/ocaml/docs/index_class_types.html
@@ -0,0 +1,17 @@
+<html>
+<head>
+<link rel="stylesheet" href="style.css" type="text/css">
+<meta content="text/html; charset=iso-8859-1" http-equiv="Content-Type">
+<meta name="viewport" content="width=device-width, initial-scale=1">
+<link rel="Start" href="index.html">
+<link title="Index of modules" rel=Appendix href="index_modules.html">
+<link title="Main" rel="Chapter" href="Main.html"><title>Index of class types</title>
+</head>
+<body>
+<div class="navbar">&nbsp;<a class="up" href="index.html" title="Index">Up</a>
+&nbsp;</div>
+<h1>Index of class types</h1>
+<table>
+</table>
+</body>
+</html>
diff --git a/ocaml/docs/index_classes.html b/ocaml/docs/index_classes.html
new file mode 100644
index 0000000..08c083b
--- /dev/null
+++ b/ocaml/docs/index_classes.html
@@ -0,0 +1,17 @@
+<html>
+<head>
+<link rel="stylesheet" href="style.css" type="text/css">
+<meta content="text/html; charset=iso-8859-1" http-equiv="Content-Type">
+<meta name="viewport" content="width=device-width, initial-scale=1">
+<link rel="Start" href="index.html">
+<link title="Index of modules" rel=Appendix href="index_modules.html">
+<link title="Main" rel="Chapter" href="Main.html"><title>Index of classes</title>
+</head>
+<body>
+<div class="navbar">&nbsp;<a class="up" href="index.html" title="Index">Up</a>
+&nbsp;</div>
+<h1>Index of classes</h1>
+<table>
+</table>
+</body>
+</html>
diff --git a/ocaml/docs/index_exceptions.html b/ocaml/docs/index_exceptions.html
new file mode 100644
index 0000000..0767720
--- /dev/null
+++ b/ocaml/docs/index_exceptions.html
@@ -0,0 +1,17 @@
+<html>
+<head>
+<link rel="stylesheet" href="style.css" type="text/css">
+<meta content="text/html; charset=iso-8859-1" http-equiv="Content-Type">
+<meta name="viewport" content="width=device-width, initial-scale=1">
+<link rel="Start" href="index.html">
+<link title="Index of modules" rel=Appendix href="index_modules.html">
+<link title="Main" rel="Chapter" href="Main.html"><title>Index of exceptions</title>
+</head>
+<body>
+<div class="navbar">&nbsp;<a class="up" href="index.html" title="Index">Up</a>
+&nbsp;</div>
+<h1>Index of exceptions</h1>
+<table>
+</table>
+</body>
+</html>
diff --git a/ocaml/docs/index_extensions.html b/ocaml/docs/index_extensions.html
new file mode 100644
index 0000000..38625df
--- /dev/null
+++ b/ocaml/docs/index_extensions.html
@@ -0,0 +1,17 @@
+<html>
+<head>
+<link rel="stylesheet" href="style.css" type="text/css">
+<meta content="text/html; charset=iso-8859-1" http-equiv="Content-Type">
+<meta name="viewport" content="width=device-width, initial-scale=1">
+<link rel="Start" href="index.html">
+<link title="Index of modules" rel=Appendix href="index_modules.html">
+<link title="Main" rel="Chapter" href="Main.html"><title>Index of extensions</title>
+</head>
+<body>
+<div class="navbar">&nbsp;<a class="up" href="index.html" title="Index">Up</a>
+&nbsp;</div>
+<h1>Index of extensions</h1>
+<table>
+</table>
+</body>
+</html>
diff --git a/ocaml/docs/index_methods.html b/ocaml/docs/index_methods.html
new file mode 100644
index 0000000..7debe46
--- /dev/null
+++ b/ocaml/docs/index_methods.html
@@ -0,0 +1,17 @@
+<html>
+<head>
+<link rel="stylesheet" href="style.css" type="text/css">
+<meta content="text/html; charset=iso-8859-1" http-equiv="Content-Type">
+<meta name="viewport" content="width=device-width, initial-scale=1">
+<link rel="Start" href="index.html">
+<link title="Index of modules" rel=Appendix href="index_modules.html">
+<link title="Main" rel="Chapter" href="Main.html"><title>Index of class methods</title>
+</head>
+<body>
+<div class="navbar">&nbsp;<a class="up" href="index.html" title="Index">Up</a>
+&nbsp;</div>
+<h1>Index of class methods</h1>
+<table>
+</table>
+</body>
+</html>
diff --git a/ocaml/docs/index_module_types.html b/ocaml/docs/index_module_types.html
new file mode 100644
index 0000000..0b75a38
--- /dev/null
+++ b/ocaml/docs/index_module_types.html
@@ -0,0 +1,17 @@
+<html>
+<head>
+<link rel="stylesheet" href="style.css" type="text/css">
+<meta content="text/html; charset=iso-8859-1" http-equiv="Content-Type">
+<meta name="viewport" content="width=device-width, initial-scale=1">
+<link rel="Start" href="index.html">
+<link title="Index of modules" rel=Appendix href="index_modules.html">
+<link title="Main" rel="Chapter" href="Main.html"><title>Index of module types</title>
+</head>
+<body>
+<div class="navbar">&nbsp;<a class="up" href="index.html" title="Index">Up</a>
+&nbsp;</div>
+<h1>Index of module types</h1>
+<table>
+</table>
+</body>
+</html>
diff --git a/ocaml/docs/index_modules.html b/ocaml/docs/index_modules.html
new file mode 100644
index 0000000..b6588a3
--- /dev/null
+++ b/ocaml/docs/index_modules.html
@@ -0,0 +1,20 @@
+<html>
+<head>
+<link rel="stylesheet" href="style.css" type="text/css">
+<meta content="text/html; charset=iso-8859-1" http-equiv="Content-Type">
+<meta name="viewport" content="width=device-width, initial-scale=1">
+<link rel="Start" href="index.html">
+<link title="Index of modules" rel=Appendix href="index_modules.html">
+<link title="Main" rel="Chapter" href="Main.html"><title>Index of modules</title>
+</head>
+<body>
+<div class="navbar">&nbsp;<a class="up" href="index.html" title="Index">Up</a>
+&nbsp;</div>
+<h1>Index of modules</h1>
+<table>
+<tr><td align="left"><div>M</div></td></tr>
+<tr><td><a href="Main.html">Main</a> </td>
+<td></td></tr>
+</table>
+</body>
+</html>
diff --git a/ocaml/docs/index_types.html b/ocaml/docs/index_types.html
new file mode 100644
index 0000000..61efcda
--- /dev/null
+++ b/ocaml/docs/index_types.html
@@ -0,0 +1,17 @@
+<html>
+<head>
+<link rel="stylesheet" href="style.css" type="text/css">
+<meta content="text/html; charset=iso-8859-1" http-equiv="Content-Type">
+<meta name="viewport" content="width=device-width, initial-scale=1">
+<link rel="Start" href="index.html">
+<link title="Index of modules" rel=Appendix href="index_modules.html">
+<link title="Main" rel="Chapter" href="Main.html"><title>Index of types</title>
+</head>
+<body>
+<div class="navbar">&nbsp;<a class="up" href="index.html" title="Index">Up</a>
+&nbsp;</div>
+<h1>Index of types</h1>
+<table>
+</table>
+</body>
+</html>
diff --git a/ocaml/docs/index_values.html b/ocaml/docs/index_values.html
new file mode 100644
index 0000000..fc7294b
--- /dev/null
+++ b/ocaml/docs/index_values.html
@@ -0,0 +1,17 @@
+<html>
+<head>
+<link rel="stylesheet" href="style.css" type="text/css">
+<meta content="text/html; charset=iso-8859-1" http-equiv="Content-Type">
+<meta name="viewport" content="width=device-width, initial-scale=1">
+<link rel="Start" href="index.html">
+<link title="Index of modules" rel=Appendix href="index_modules.html">
+<link title="Main" rel="Chapter" href="Main.html"><title>Index of values</title>
+</head>
+<body>
+<div class="navbar">&nbsp;<a class="up" href="index.html" title="Index">Up</a>
+&nbsp;</div>
+<h1>Index of values</h1>
+<table>
+</table>
+</body>
+</html>
diff --git a/ocaml/docs/style.css b/ocaml/docs/style.css
new file mode 100644
index 0000000..259bd49
--- /dev/null
+++ b/ocaml/docs/style.css
@@ -0,0 +1,43 @@
+.keyword { font-weight : bold ; color : Red }
+.keywordsign { color : #C04600 }
+.comment { color : Green }
+.constructor { color : Blue }
+.type { color : #5C6585 }
+.string { color : Maroon }
+.warning { color : Red ; font-weight : bold }
+.info { margin-left : 3em; margin-right: 3em }
+.param_info { margin-top: 4px; margin-left : 3em; margin-right : 3em }
+.code { color : #465F91 ; }
+.typetable { border-style : hidden }
+.paramstable { border-style : hidden ; padding: 5pt 5pt}
+tr { background-color : White }
+td.typefieldcomment { background-color : #FFFFFF ; font-size: smaller ;}
+div.sig_block {margin-left: 2em}
+*:target { background: yellow; }
+body {font: 13px sans-serif; color: black; text-align: left; padding: 5px; margin: 0}
+h1 { font-size : 20pt ; text-align: center; }
+h2 { font-size : 20pt ; text-align: center; }
+h3 { font-size : 20pt ; border: 1px solid #000000; margin-top: 5px; margin-bottom: 2px;text-align: center; background-color: #90BDFF ;padding: 2px; }
+h4 { font-size : 20pt ; border: 1px solid #000000; margin-top: 5px; margin-bottom: 2px;text-align: center; background-color: #90DDFF ;padding: 2px; }
+h5 { font-size : 20pt ; border: 1px solid #000000; margin-top: 5px; margin-bottom: 2px;text-align: center; background-color: #90EDFF ;padding: 2px; }
+h6 { font-size : 20pt ; border: 1px solid #000000; margin-top: 5px; margin-bottom: 2px;text-align: center; background-color: #90FDFF ;padding: 2px; }
+div.h7 { font-size : 20pt ; border: 1px solid #000000; margin-top: 5px; margin-bottom: 2px;text-align: center; background-color: #90BDFF ; padding: 2px; }
+div.h8 { font-size : 20pt ; border: 1px solid #000000; margin-top: 5px; margin-bottom: 2px;text-align: center; background-color: #E0FFFF ; padding: 2px; }
+div.h9 { font-size : 20pt ; border: 1px solid #000000; margin-top: 5px; margin-bottom: 2px;text-align: center; background-color: #F0FFFF ; padding: 2px; }
+div.h10 { font-size : 20pt ; border: 1px solid #000000; margin-top: 5px; margin-bottom: 2px;text-align: center; background-color: #FFFFFF ; padding: 2px; }
+a {color: #416DFF; text-decoration: none}
+a:hover {background-color: #ddd; text-decoration: underline}
+pre { margin-bottom: 4px; font-family: monospace; }
+pre.verbatim, pre.codepre { }
+.indextable {border: 1px #ddd solid; border-collapse: collapse}
+.indextable td, .indextable th {border: 1px #ddd solid; min-width: 80px}
+.indextable td.module {background-color: #eee ;  padding-left: 2px; padding-right: 2px}
+.indextable td.module a {color: #4E6272; text-decoration: none; display: block; width: 100%}
+.indextable td.module a:hover {text-decoration: underline; background-color: transparent}
+.deprecated {color: #888; font-style: italic}
+.indextable tr td div.info { margin-left: 2px; margin-right: 2px }
+ul.indexlist { margin-left: 0; padding-left: 0;}
+ul.indexlist li { list-style-type: none ; margin-left: 0; padding-left: 0; }
+ul.info-attributes {list-style: none; margin: 0; padding: 0; }
+div.info > p:first-child { margin-top:0; }
+div.info-desc > p:first-child { margin-top:0; margin-bottom:0; }
\ No newline at end of file
diff --git a/ocaml/docs/type_Main.html b/ocaml/docs/type_Main.html
new file mode 100644
index 0000000..43bb69c
--- /dev/null
+++ b/ocaml/docs/type_Main.html
@@ -0,0 +1,10 @@
+<html><head>
+<link rel="stylesheet" href="style.css" type="text/css">
+<meta content="text/html; charset=iso-8859-1" http-equiv="Content-Type">
+<meta name="viewport" content="width=device-width, initial-scale=1">
+<link rel="Start" href="index.html">
+<link title="Index of modules" rel=Appendix href="index_modules.html">
+<link title="Main" rel="Chapter" href="Main.html"><title>Main</title>
+</head>
+<body>
+<code class="code"><span class="keyword">sig</span>&nbsp;<span class="keyword">end</span></code></body></html>
diff --git a/ocaml/dune-project b/ocaml/dune-project
new file mode 100644
index 0000000..731f4b5
--- /dev/null
+++ b/ocaml/dune-project
@@ -0,0 +1,40 @@
+(lang dune 3.20)
+
+(name advent_of_code)
+
+(generate_opam_files true)
+
+(source
+ (github djoleary/advent_of_code))
+
+(authors "DJ O'Leary <dijitol@proton.me>")
+
+(maintainers "DJ O'Leary <dijitol@proton.me>")
+
+(license Unlicense)
+
+(documentation https://github.com/djoleary/advent_of_code/2025/ocaml/docs/index.html)
+
+(package
+ (name advent_of_code)
+ (synopsis "advent of code solutions for 2025")
+ (description "project aiming to solve the advent of code puzzles released for 2025")
+ (depends
+   (ocaml (>= 5.2))
+   (ppx_deriving :build)
+   (alcotest :with-test)
+   (qcheck :with-test)
+   (bisect_ppx :with-test)
+   (ppx_inline_test :with-test)
+   (ppx_expect :with-test)
+   (odoc :with-doc)
+   cmdliner
+   fmt
+   re2
+ )
+ (tags
+  ("Advent of Code")))
+
+(map_workspace_root false)
+
+; See the complete stanza docs at https://dune.readthedocs.io/en/stable/reference/dune-project/index.html
diff --git a/ocaml/flake.lock b/ocaml/flake.lock
new file mode 100644
index 0000000..3baeb69
--- /dev/null
+++ b/ocaml/flake.lock
@@ -0,0 +1,27 @@
+{
+  "nodes": {
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1763421233,
+        "narHash": "sha256-Stk9ZYRkGrnnpyJ4eqt9eQtdFWRRIvMxpNRf4sIegnw=",
+        "owner": "nixos",
+        "repo": "nixpkgs",
+        "rev": "89c2b2330e733d6cdb5eae7b899326930c2c0648",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nixos",
+        "ref": "nixos-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "nixpkgs": "nixpkgs"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}
diff --git a/ocaml/flake.nix b/ocaml/flake.nix
new file mode 100644
index 0000000..54d7b3f
--- /dev/null
+++ b/ocaml/flake.nix
@@ -0,0 +1,52 @@
+{
+  inputs = {
+    nixpkgs.url = "github:nixos/nixpkgs?ref=nixos-unstable";
+  };
+
+  outputs =
+    { nixpkgs, ... }:
+    let
+      pkgs = nixpkgs.legacyPackages.x86_64-linux;
+    in
+    {
+      devShells.x86_64-linux.default =
+        let
+          ocamlPackages = with pkgs.ocaml-ng.ocamlPackages_5_2; [
+            ocaml
+
+            dune_3 # build system
+
+            pkgs.opam # package manager
+            findlib # library manager
+
+            ocaml-lsp # language server
+            earlybird # debug adapter
+            ocamlformat # formatter
+
+            utop # REPL
+
+            odoc # documentation generator
+
+            alcotest # unit test framework
+            bisect_ppx # test coverage
+            qcheck-core # property-based testing
+            qcheck-alcotest # property-based testing
+            janeStreet.ppx_inline_test # inline test library
+            janeStreet.ppx_expect # inline test library
+
+            janeStreet.re2 # regular expression library
+            fmt # pretty printing library
+            cmdliner # command line library
+            ppx_deriving # derivers
+            logs # logging library
+          ];
+          sysTools = with pkgs; [
+            go-task
+            gh
+          ];
+        in
+        pkgs.mkShell {
+          buildInputs = ocamlPackages ++ sysTools;
+        };
+    };
+}
\ No newline at end of file
diff --git a/ocaml/lib/application/d01p01.ml b/ocaml/lib/application/d01p01.ml
new file mode 100644
index 0000000..206e757
--- /dev/null
+++ b/ocaml/lib/application/d01p01.ml
@@ -0,0 +1,53 @@
+open Domain.D01p01
+
+let err_empty_input = "input is empty"
+
+let rec input_to_lines input =
+  let lines =
+    String.split_on_char '\n' input |> List.filter (fun l -> l <> "")
+  in
+  pp_lines lines ; lines
+
+and pp_lines = function
+  | [] ->
+      ()
+  | h :: t ->
+      Logs.debug (fun m -> m "Line=%s" h) ;
+      pp_lines t
+
+let parse_line line =
+  Scanf.sscanf line "%c%d" (fun d n ->
+      match d with
+      | 'L' ->
+          Dial.Left n
+      | 'R' ->
+          Dial.Right n
+      | _ ->
+          failwith "invalid direction" )
+
+let lines_to_turns =
+  List.map (fun (l : string) ->
+      Logs.debug (fun m -> m "parsing %s into turn" l) ;
+      let turn = parse_line l in
+      Logs.debug (fun m -> m "%s" (Dial.pp_direction turn)) ;
+      turn )
+
+let rec turn_aux count current = function
+  | [] ->
+      count
+  | h :: t ->
+      let current' = Dial.turn current h in
+      Logs.debug (fun m -> m "dial at %d" (Dial.to_int current')) ;
+      if Dial.to_int current' = 0 then turn_aux (count + 1) current' t
+      else turn_aux count current' t
+
+let turn current = turn_aux 0 current
+
+let solve input () =
+  if input = "" then Error err_empty_input
+  else
+    let lines = input_to_lines input in
+    let turns = lines_to_turns lines in
+    let start = Dial.start in
+    let answer = turn start turns in
+    Ok answer
diff --git a/ocaml/lib/application/d01p01.mli b/ocaml/lib/application/d01p01.mli
new file mode 100644
index 0000000..2eecf19
--- /dev/null
+++ b/ocaml/lib/application/d01p01.mli
@@ -0,0 +1,4 @@
+val solve : string -> unit -> (int, string) result
+(** [solve input ()] is the solution for the first part of the first day of advent of code 2025 for [input].
+    The solution for an empty input is [None].
+    Requires: [input] to be a multiline string using `\n` as it's line separator. *)
diff --git a/ocaml/lib/application/d01p02.ml b/ocaml/lib/application/d01p02.ml
new file mode 100644
index 0000000..7910486
--- /dev/null
+++ b/ocaml/lib/application/d01p02.ml
@@ -0,0 +1,55 @@
+open Domain.D01p02
+
+let err_empty_input = "input is empty"
+
+let rec input_to_lines input =
+  let lines =
+    String.split_on_char '\n' input |> List.filter (fun l -> l <> "")
+  in
+  pp_lines lines ; lines
+
+and pp_lines = function
+  | [] ->
+      ()
+  | h :: t ->
+      Logs.debug (fun m -> m "Line=%s" h) ;
+      pp_lines t
+
+let parse_line line =
+  Scanf.sscanf line "%c%d" (fun d n ->
+      match d with
+      | 'L' ->
+          Dial.Left n
+      | 'R' ->
+          Dial.Right n
+      | _ ->
+          failwith "invalid direction" )
+
+let lines_to_turns =
+  List.map (fun (l : string) ->
+      Logs.debug (fun m -> m "parsing %s into turn" l) ;
+      let turn = parse_line l in
+      Logs.debug (fun m -> m "%s" (Dial.pp_direction turn)) ;
+      turn )
+
+let rec turn_aux count dial = function
+  | [] ->
+      count
+  | h :: t -> (
+      let dial_and_count = Turner.turn dial count h in
+      match dial_and_count with
+      | dial', count' ->
+          Logs.debug (fun m ->
+              m "(dial=%d, count=%d)" (Dial.to_int dial') count' ) ;
+          turn_aux count' dial' t )
+
+let turn current = turn_aux 0 current
+
+let solve input () =
+  if input = "" then Error err_empty_input
+  else
+    let lines = input_to_lines input in
+    let turns = lines_to_turns lines in
+    let start = Dial.start in
+    let answer = turn start turns in
+    Ok answer
diff --git a/ocaml/lib/application/d01p02.mli b/ocaml/lib/application/d01p02.mli
new file mode 100644
index 0000000..9e9a2f2
--- /dev/null
+++ b/ocaml/lib/application/d01p02.mli
@@ -0,0 +1,4 @@
+val solve : string -> unit -> (int, string) result
+(** [solve input ()] is the solution for the second part of the first day of advent of code 2025 for [input].
+    The solution for an empty input is [Error msg].
+    Requires: [input] to be a multiline string using `\n` as it's line separator. *)
diff --git a/ocaml/lib/application/d02p01.ml b/ocaml/lib/application/d02p01.ml
new file mode 100644
index 0000000..f313149
--- /dev/null
+++ b/ocaml/lib/application/d02p01.ml
@@ -0,0 +1,54 @@
+open Domain.D02p01
+
+let err_empty_input = "input is empty"
+
+(** [input_to_lines input] is a list of strings that have been split on ','.
+    Example: [input_to_lines "12-34,56-78,90-100"] becomes the list \[ "12-34"; "56-78"; "90-100" \].
+    Requires: [input] to be a string in the format "12-34,56-78,90-100". *)
+let input_to_lines input = input |> String.trim |> String.split_on_char ','
+
+let pp_lines = Seq.iter (fun l -> Logs.debug (fun m -> m "line=%s" l))
+
+(** [lines_to_ranges line] is a list of [Range]s found on [line]. *)
+let lines_to_ranges =
+  Seq.map (fun line ->
+      Scanf.sscanf line "%d-%d" (fun id1 id2 -> Range.create (id1, id2)) )
+
+let pp_ranges = Seq.iter (fun r -> Logs.debug (fun m -> m "%s" (Range.pp r)))
+
+(** [collect_all ranges] is an unsorted list of [ID]s within the [ranges] (inclusive). *)
+let collect_all =
+  Seq.concat_map (fun range -> List.to_seq (Range.collect range))
+
+let pp_collection = Seq.iter (fun c -> Logs.debug (fun m -> m "%s" (ID.pp c)))
+
+(** [rules] is a list of rules that [ID]s must pass to be considered invalid. *)
+let rules =
+  [ (fun id -> String.length (ID.to_string id) mod 2 = 0)
+  ; (fun id ->
+      let id' = ID.to_string id in
+      let id_len = String.length id' in
+      let left = String.sub id' 0 (id_len / 2) in
+      let right = String.sub id' (id_len / 2) (id_len / 2) in
+      String.equal left right ) ]
+
+(** [is_invalid id] is [true] for an [id] that passes all of the rules and is considered invalid. *)
+let is_invalid = ID.validate rules
+
+(** [passthrough_with_logs logger lst] is [lst] with the side-effects caused by calling [logger] on [lst]. *)
+let passthrough_with_logs logger lst = logger lst ; lst
+
+let solve input () =
+  if input = "" then Error err_empty_input
+  else
+    let answer =
+      input |> input_to_lines |> List.to_seq
+      |> passthrough_with_logs pp_lines
+      |> lines_to_ranges
+      |> passthrough_with_logs pp_ranges
+      |> collect_all
+      |> passthrough_with_logs pp_collection
+      |> Seq.filter is_invalid
+      |> Seq.fold_left (fun acc id -> acc + ID.to_int id) 0
+    in
+    Ok answer
diff --git a/ocaml/lib/application/d02p01.mli b/ocaml/lib/application/d02p01.mli
new file mode 100644
index 0000000..8a8eb32
--- /dev/null
+++ b/ocaml/lib/application/d02p01.mli
@@ -0,0 +1,4 @@
+val solve : string -> unit -> (int, string) result
+(** [solve input ()] is the solution for the first part of the second day of advent of code 2025 for [input].
+    The solution for an empty input is [Error msg].
+    Requires: [input] to be a string. *)
diff --git a/ocaml/lib/application/d02p02.ml b/ocaml/lib/application/d02p02.ml
new file mode 100644
index 0000000..d062f7b
--- /dev/null
+++ b/ocaml/lib/application/d02p02.ml
@@ -0,0 +1,86 @@
+open Domain.D02p02
+
+(* Errors *)
+
+let err_empty_input = "input is empty"
+
+(* Logging *)
+
+(** [passthrough_with_logs logger lst] is [lst] with the side-effects caused by calling [logger] on [lst]. *)
+let passthrough_with_logs logger lst = logger lst ; lst
+
+(** [input_to_lines input] is a list of strings that have been split on ','.
+    Example: [input_to_lines "12-34,56-78,90-100"] becomes the list \[ "12-34"; "56-78"; "90-100" \].
+    Requires: [input] to be a string in the format "12-34,56-78,90-100". *)
+let input_to_lines input = input |> String.trim |> String.split_on_char ','
+
+let pp_lines = Seq.iter (fun l -> Logs.debug (fun m -> m "line=%s" l))
+
+let pp_ranges = Seq.iter (fun r -> Logs.debug (fun m -> m "%s" (Range.pp r)))
+
+let pp_collection = Seq.iter (fun c -> Logs.debug (fun m -> m "%s" (ID.pp c)))
+
+(* Core Logic *)
+
+(** [lines_to_ranges line] is a list of [Range]s found on [line]. *)
+let lines_to_ranges =
+  Seq.map (fun line ->
+      Scanf.sscanf line "%d-%d" (fun id1 id2 -> Range.create (id1, id2)) )
+
+(** [collect_all ranges] is an unsorted list of [ID]s within the [ranges] (inclusive). *)
+let collect_all =
+  Seq.concat_map (fun range -> List.to_seq (Range.collect range))
+
+(** [string_to_segments count string] is a list containing [count] string segments with of equal length.
+    Requires: length of [string] to be divisible by [count]
+    and [count] to be greater than or equal to zero *)
+let rec string_to_segments s =
+  let segment_lengths = possible_segment_lengths s in
+  List.map (fun c -> string_to_segments_aux [] c s |> List.rev) segment_lengths
+
+(** [possible_segment_lengths s] is a list of segment sizes that fit within [s]
+    that must be checked to rule out a repeating pattern. *)
+and possible_segment_lengths s =
+  List.init (String.length s) (fun x -> x + 1)
+  |> List.filter (fun x -> x != 1 && String.length s mod x = 0)
+
+and string_to_segments_aux segments count string =
+  match List.length segments = count with
+  | true ->
+      segments
+  | false ->
+      let segment_start = String.length string / count * List.length segments in
+      let segment_len = String.length string / count in
+      string_to_segments_aux
+        (String.sub string segment_start segment_len :: segments)
+        count string
+
+(** [cmp_segments segments] is true is all segments are equal *)
+let cmp_segments segments =
+  List.length (List.sort_uniq String.compare segments) = 1
+
+(** [is_invalid id] is [true] for an [id] that is considered invalid. *)
+let is_invalid id =
+  Logs.debug (fun m -> m "CHECKING ID=%s" id) ;
+  let repeating_patterns =
+    id |> string_to_segments |> List.filter cmp_segments
+  in
+  List.iter
+    (fun l -> Logs.debug (fun m -> m "HAS SUBPATTERN=%s" (List.hd l)))
+    repeating_patterns ;
+  List.length repeating_patterns > 0
+
+let solve input () =
+  if input = "" then Error err_empty_input
+  else
+    let answer =
+      input |> input_to_lines |> List.to_seq
+      |> passthrough_with_logs pp_lines
+      |> lines_to_ranges
+      |> passthrough_with_logs pp_ranges
+      |> collect_all
+      |> passthrough_with_logs pp_collection
+      |> Seq.map ID.to_string |> Seq.filter is_invalid
+      |> Seq.fold_left (fun acc id -> acc + int_of_string id) 0
+    in
+    Ok answer
diff --git a/ocaml/lib/application/d02p02.mli b/ocaml/lib/application/d02p02.mli
new file mode 100644
index 0000000..8a8eb32
--- /dev/null
+++ b/ocaml/lib/application/d02p02.mli
@@ -0,0 +1,4 @@
+val solve : string -> unit -> (int, string) result
+(** [solve input ()] is the solution for the first part of the second day of advent of code 2025 for [input].
+    The solution for an empty input is [Error msg].
+    Requires: [input] to be a string. *)
diff --git a/ocaml/lib/application/d03p01.ml b/ocaml/lib/application/d03p01.ml
new file mode 100644
index 0000000..522f5d0
--- /dev/null
+++ b/ocaml/lib/application/d03p01.ml
@@ -0,0 +1,23 @@
+open Domain.D03p01
+
+let err_empty_input = "input is empty"
+
+let to_lines s =
+  s |> String.split_on_char '\n' |> List.map String.trim
+  |> List.filter (fun l -> l <> "")
+
+let solve input () =
+  if input = "" then Error err_empty_input
+  else
+    let answer =
+      input |> to_lines |> List.to_seq
+      |> Seq.map BatteryBank.of_string
+      |> Seq.mapi (fun idx bb ->
+          let joltage = BatteryBank.highest_joltage bb in
+          Logs.debug (fun m ->
+              m "%d line=%s highest_joltage=%d" (idx + 1) (BatteryBank.pp bb)
+                joltage ) ;
+          joltage )
+      |> Seq.fold_left ( + ) 0
+    in
+    Ok answer
diff --git a/ocaml/lib/application/d03p01.mli b/ocaml/lib/application/d03p01.mli
new file mode 100644
index 0000000..31dd0cd
--- /dev/null
+++ b/ocaml/lib/application/d03p01.mli
@@ -0,0 +1,4 @@
+val solve : string -> unit -> (int, string) result
+(** [solve input ()] is the solution for the first part of the third day of advent of code 2025 for [input].
+    The solution for an empty input is [Error msg].
+    Requires: [input] to be a string. *)
diff --git a/ocaml/lib/application/d03p02.ml b/ocaml/lib/application/d03p02.ml
new file mode 100644
index 0000000..743c658
--- /dev/null
+++ b/ocaml/lib/application/d03p02.ml
@@ -0,0 +1,23 @@
+open Domain.D03p02
+
+let err_empty_input = "input is empty"
+
+let to_lines s =
+  s |> String.split_on_char '\n' |> List.map String.trim
+  |> List.filter (fun l -> l <> "")
+
+let solve input () =
+  if input = "" then Error err_empty_input
+  else
+    let answer =
+      input |> to_lines |> List.to_seq
+      |> Seq.map BatteryBank.of_string
+      |> Seq.mapi (fun idx bb ->
+          let joltage = BatteryBank.highest_joltage bb in
+          Logs.debug (fun m ->
+              m "%d line=%s highest_joltage=%d" (idx + 1) (BatteryBank.pp bb)
+                joltage ) ;
+          joltage )
+      |> Seq.fold_left ( + ) 0
+    in
+    Ok answer
diff --git a/ocaml/lib/application/d03p02.mli b/ocaml/lib/application/d03p02.mli
new file mode 100644
index 0000000..93d3b98
--- /dev/null
+++ b/ocaml/lib/application/d03p02.mli
@@ -0,0 +1,4 @@
+val solve : string -> unit -> (int, string) result
+(** [solve input ()] is the solution for the second part of the third day of advent of code 2025 for [input].
+    The solution for an empty input is [Error msg].
+    Requires: [input] to be a string. *)
diff --git a/ocaml/lib/application/d04p01.ml b/ocaml/lib/application/d04p01.ml
new file mode 100644
index 0000000..7c69de4
--- /dev/null
+++ b/ocaml/lib/application/d04p01.ml
@@ -0,0 +1,48 @@
+open Domain
+
+let err_empty_input = "input is empty"
+
+let rec solve input () =
+  if input = "" then Error err_empty_input
+  else
+    let matrix = Matrix.M.of_string input in
+    let count_paper lst = List.length @@ List.filter (fun c -> c <> ".") lst in
+    let accessible_rolls_of_paper = ref 0 in
+    for y = 0 to Array.length matrix - 1 do
+      for x = 0 to Array.length matrix.(y) - 1 do
+        if matrix.(y).(x) = "." then ()
+        else
+          let neighbour_coords = Matrix.M.get_valid_neighbours matrix x y in
+          let neighbours =
+            List.map
+              (fun (x', y') -> Matrix.M.get matrix x' y')
+              neighbour_coords
+          in
+          let paper_count = count_paper neighbours in
+          let is_accessible = paper_count < 4 in
+          if is_accessible then
+            accessible_rolls_of_paper := !accessible_rolls_of_paper + 1 ;
+          print_iteration_debug_msg x y neighbour_coords neighbours paper_count
+            is_accessible
+      done
+    done ;
+    Ok !accessible_rolls_of_paper
+
+and print_iteration_debug_msg x y neighbour_coords neighbours paper_count
+    is_accessible =
+  Logs.debug (fun m ->
+      m
+        "coords=(%d,%d) neighbour_coords=[%s] neighbours=[%s] paper=%d \
+         is_accessible=%B"
+        x y
+        (List.fold_left
+           (fun acc (x, y) ->
+             if acc = "" then
+               " (" ^ string_of_int x ^ "," ^ string_of_int y ^ "); "
+             else acc ^ "(" ^ string_of_int x ^ "," ^ string_of_int y ^ "); " )
+           "" neighbour_coords )
+        (List.fold_left
+           (fun acc neighbour ->
+             if acc = "" then " " ^ neighbour ^ "; " else acc ^ neighbour ^ "; " )
+           "" neighbours )
+        paper_count is_accessible )
diff --git a/ocaml/lib/application/d04p01.mli b/ocaml/lib/application/d04p01.mli
new file mode 100644
index 0000000..873acff
--- /dev/null
+++ b/ocaml/lib/application/d04p01.mli
@@ -0,0 +1,4 @@
+val solve : string -> unit -> (int, string) result
+(** [solve input ()] is the solution for the first part of the fourth day of advent of code 2025 for [input].
+    The solution for an empty input is [Error msg].
+    Requires: [input] to be a string. *)
diff --git a/ocaml/lib/application/d04p02.ml b/ocaml/lib/application/d04p02.ml
new file mode 100644
index 0000000..75b1236
--- /dev/null
+++ b/ocaml/lib/application/d04p02.ml
@@ -0,0 +1,64 @@
+open Domain
+
+let err_empty_input = "input is empty"
+
+let rec count_accessible_rolls matrix =
+  let count_paper lst = List.length @@ List.filter (fun c -> c = "@") lst in
+  let accessible_rolls_of_paper = ref [] in
+  let no_change = ref false in
+  while not !no_change do
+    let accessible_rolls_of_paper' = !accessible_rolls_of_paper in
+    count_accessible_rolls_aux matrix count_paper accessible_rolls_of_paper ;
+    if
+      List.length accessible_rolls_of_paper'
+      = List.length !accessible_rolls_of_paper
+    then no_change := true
+  done ;
+  List.length !accessible_rolls_of_paper
+
+and count_accessible_rolls_aux matrix count_paper accessible_rolls_of_paper =
+  for y = 0 to Array.length matrix - 1 do
+    for x = 0 to Array.length matrix.(y) - 1 do
+      if matrix.(y).(x) = "." then ()
+      else
+        let neighbour_coords = Matrix.M.get_valid_neighbours matrix x y in
+        let neighbours =
+          List.map (fun (nx, ny) -> Matrix.M.get matrix nx ny) neighbour_coords
+        in
+        let paper_count = count_paper neighbours in
+        let is_accessible = paper_count < 4 in
+        if is_accessible then
+          accessible_rolls_of_paper := (x, y) :: !accessible_rolls_of_paper ;
+        print_iteration_debug_msg x y neighbour_coords neighbours paper_count
+          is_accessible
+    done
+  done ;
+  List.iter
+    (fun (x', y') -> Matrix.M.set matrix x' y' ".")
+    !accessible_rolls_of_paper
+
+and print_iteration_debug_msg x y neighbour_coords neighbours paper_count
+    is_accessible =
+  Logs.debug (fun m ->
+      m
+        "coords=(%d,%d) neighbour_coords=[%s] neighbours=[%s] paper=%d \
+         is_accessible=%B"
+        x y
+        (List.fold_left
+           (fun acc (x, y) ->
+             if acc = "" then
+               " (" ^ string_of_int x ^ "," ^ string_of_int y ^ "); "
+             else acc ^ "(" ^ string_of_int x ^ "," ^ string_of_int y ^ "); " )
+           "" neighbour_coords )
+        (List.fold_left
+           (fun acc neighbour ->
+             if acc = "" then " " ^ neighbour ^ "; " else acc ^ neighbour ^ "; " )
+           "" neighbours )
+        paper_count is_accessible )
+
+let solve input () =
+  if input = "" then Error err_empty_input
+  else
+    let matrix = Matrix.M.of_string input in
+    let accessible_rolls_of_paper = count_accessible_rolls matrix in
+    Ok accessible_rolls_of_paper
diff --git a/ocaml/lib/application/d04p02.mli b/ocaml/lib/application/d04p02.mli
new file mode 100644
index 0000000..388ec56
--- /dev/null
+++ b/ocaml/lib/application/d04p02.mli
@@ -0,0 +1,4 @@
+val solve : string -> unit -> (int, string) result
+(** [solve input ()] is the solution for the second part of the fourth day of advent of code 2025 for [input].
+    The solution for an empty input is [Error msg].
+    Requires: [input] to be a string. *)
diff --git a/ocaml/lib/application/d05p01.ml b/ocaml/lib/application/d05p01.ml
new file mode 100644
index 0000000..4bf79ab
--- /dev/null
+++ b/ocaml/lib/application/d05p01.ml
@@ -0,0 +1,3 @@
+let err_empty_input = "input is empty"
+
+let solve input () = if input = "" then Error err_empty_input else Ok 0
diff --git a/ocaml/lib/application/d05p01.mli b/ocaml/lib/application/d05p01.mli
new file mode 100644
index 0000000..85c3dd5
--- /dev/null
+++ b/ocaml/lib/application/d05p01.mli
@@ -0,0 +1,4 @@
+val solve : string -> unit -> (int, string) result
+(** [solve input ()] is the solution for the first part of the five day of advent of code 2025 for [input].
+    The solution for an empty input is [Error msg].
+    Requires: [input] to be a string. *)
diff --git a/ocaml/lib/application/d06p01.ml b/ocaml/lib/application/d06p01.ml
new file mode 100644
index 0000000..9425810
--- /dev/null
+++ b/ocaml/lib/application/d06p01.ml
@@ -0,0 +1,50 @@
+let err_empty_input = "input is empty"
+
+let log_matrix matrix =
+  let open Domain.Matrix in
+  Logs.debug (fun m -> m "%s" (M.of_list matrix |> M.pp (fun elt -> elt)))
+
+let log_list lst =
+  Logs.debug (fun m ->
+      m "[%s]" (List.fold_left (fun acc i -> acc ^ i ^ "; ") " " lst) )
+
+type operation = Mult | Add
+
+let solve input () =
+  if input = "" then Error err_empty_input
+  else
+    let input' = Parser.columns_of_string input in
+    assert (input' <> []) ;
+    log_matrix input' ;
+    let nums =
+      List.map (List.filter (fun i -> i <> "*" && i <> "+")) input'
+      |> List.map
+         @@ List.map (fun n ->
+             Logs.debug (fun m -> m "peeking: %s" n) ;
+             int_of_string n )
+    and ops =
+      List.map (List.filter (fun i -> i = "*" || i = "+")) input'
+      |> List.concat
+      |> List.map (fun op ->
+          match op with
+          | "*" ->
+              Mult
+          | "+" ->
+              Add
+          | _ ->
+              failwith "case not covered" )
+    in
+    let answer =
+      List.map2
+        (fun op num_lst ->
+          match op with
+          | Add ->
+              List.fold_left (fun acc i -> acc + i) 0 num_lst
+          | Mult ->
+              List.fold_left (fun acc i -> acc * i) 1 num_lst )
+        ops nums
+      |> fun lst ->
+      log_list @@ List.map string_of_int lst ;
+      lst |> List.fold_left ( + ) 0
+    in
+    Ok answer
diff --git a/ocaml/lib/application/d06p01.mli b/ocaml/lib/application/d06p01.mli
new file mode 100644
index 0000000..b3abc1e
--- /dev/null
+++ b/ocaml/lib/application/d06p01.mli
@@ -0,0 +1,4 @@
+val solve : string -> unit -> (int, string) result
+(** [solve input ()] is the solution for the first part of the sixth day of advent of code 2025 for [input].
+    The solution for an empty input is [Error msg].
+    Requires: [input] to be a string. *)
diff --git a/ocaml/lib/application/d06p02.ml b/ocaml/lib/application/d06p02.ml
new file mode 100644
index 0000000..9425810
--- /dev/null
+++ b/ocaml/lib/application/d06p02.ml
@@ -0,0 +1,50 @@
+let err_empty_input = "input is empty"
+
+let log_matrix matrix =
+  let open Domain.Matrix in
+  Logs.debug (fun m -> m "%s" (M.of_list matrix |> M.pp (fun elt -> elt)))
+
+let log_list lst =
+  Logs.debug (fun m ->
+      m "[%s]" (List.fold_left (fun acc i -> acc ^ i ^ "; ") " " lst) )
+
+type operation = Mult | Add
+
+let solve input () =
+  if input = "" then Error err_empty_input
+  else
+    let input' = Parser.columns_of_string input in
+    assert (input' <> []) ;
+    log_matrix input' ;
+    let nums =
+      List.map (List.filter (fun i -> i <> "*" && i <> "+")) input'
+      |> List.map
+         @@ List.map (fun n ->
+             Logs.debug (fun m -> m "peeking: %s" n) ;
+             int_of_string n )
+    and ops =
+      List.map (List.filter (fun i -> i = "*" || i = "+")) input'
+      |> List.concat
+      |> List.map (fun op ->
+          match op with
+          | "*" ->
+              Mult
+          | "+" ->
+              Add
+          | _ ->
+              failwith "case not covered" )
+    in
+    let answer =
+      List.map2
+        (fun op num_lst ->
+          match op with
+          | Add ->
+              List.fold_left (fun acc i -> acc + i) 0 num_lst
+          | Mult ->
+              List.fold_left (fun acc i -> acc * i) 1 num_lst )
+        ops nums
+      |> fun lst ->
+      log_list @@ List.map string_of_int lst ;
+      lst |> List.fold_left ( + ) 0
+    in
+    Ok answer
diff --git a/ocaml/lib/application/d06p02.mli b/ocaml/lib/application/d06p02.mli
new file mode 100644
index 0000000..49444de
--- /dev/null
+++ b/ocaml/lib/application/d06p02.mli
@@ -0,0 +1,4 @@
+val solve : string -> unit -> (int, string) result
+(** [solve input ()] is the solution for the second part of the sixth day of advent of code 2025 for [input].
+    The solution for an empty input is [Error msg].
+    Requires: [input] to be a string. *)
diff --git a/ocaml/lib/application/dune b/ocaml/lib/application/dune
new file mode 100644
index 0000000..b78613a
--- /dev/null
+++ b/ocaml/lib/application/dune
@@ -0,0 +1,14 @@
+(library
+  (name application)
+  (libraries
+    domain
+    fmt
+    logs)
+  (inline_tests)
+  (preprocess
+    (pps
+      ppx_deriving.show
+      ppx_deriving.eq
+      ppx_deriving.ord
+      ppx_inline_test
+      ppx_expect)))
diff --git a/ocaml/lib/application/parser.ml b/ocaml/lib/application/parser.ml
new file mode 100644
index 0000000..099900b
--- /dev/null
+++ b/ocaml/lib/application/parser.ml
@@ -0,0 +1,36 @@
+(** [rows_of_string s] is a list of strings where each element is a row of [s]. *)
+let rows_of_string s =
+  s |> String.split_on_char '\n'
+  |> List.filter_map (fun l ->
+      let trimmed = String.trim l in
+      if trimmed <> "" then Some trimmed else None )
+
+(** [columns_of_string ?sep s] is a list of strings where each element is
+    a column of [s] where each column is separated by [sep]. *)
+let rec columns_of_string ?(sep = ' ') s =
+  rows_of_string s
+  |> List.map (fun l ->
+      l |> String.split_on_char sep |> List.filter (fun l -> l <> "") )
+  |> transpose
+
+(** [group_columns lst] is a list where the first element of each
+    sublist of [lst] is grouped in [acc] and so on for the rest of the elements.
+    Example: [group_columns [] \[\["abc"; "def"\]; \["ghi"; "jkl"\]\]] is the list [\[\["abc";"ghi"\];\["def";"jkl"\]\]]. *)
+and transpose lst =
+  assert (lst <> []) ;
+  if List.mem [] lst then []
+  else List.map List.hd lst :: transpose (List.map List.tl lst)
+
+let%expect_test "rows correctly parsed" =
+  let have = {| abc def
+    ghi jkl |} in
+  let rows = rows_of_string have in
+  List.iter (fun c -> print_string (c ^ " ")) rows ;
+  [%expect {| abc def ghi jkl |}]
+
+let%expect_test "columns correctly parsed" =
+  let have = {| abc def
+    ghi jkl |} in
+  let cols = columns_of_string have in
+  List.iter (fun row -> List.iter (fun c -> print_string (c ^ " ")) row) cols ;
+  [%expect {| abc ghi def jkl |}]
diff --git a/ocaml/lib/domain/d01p01.ml b/ocaml/lib/domain/d01p01.ml
new file mode 100644
index 0000000..6b531f4
--- /dev/null
+++ b/ocaml/lib/domain/d01p01.ml
@@ -0,0 +1,76 @@
+module Dial : sig
+  (** [t] is a dial between 0 and 99 inclusive *)
+  type t
+
+  (** [direction] is a direction the dial can be turned *)
+  type direction = Left of int | Right of int
+
+  val start : t
+  (** [start] is the initial state of the dial *)
+
+  val dial_out_of_range : string
+  (** [dial_out_of_range] is the error message when the dial is out of range *)
+
+  val turn : t -> direction -> t
+  (** [turn current direction] is the new state of the dial after turning [direction] from [current] *)
+
+  val to_string : t -> string
+  (** [to_string t] is the string representation of [t] *)
+
+  val to_int : t -> int
+  (** [to_int t] is the integer representation of [t] *)
+
+  val pp_direction : direction -> string
+end = struct
+  (** [t] is an int between 0 and 99 inclusive *)
+  type t = int
+
+  type direction = Left of int | Right of int
+
+  let start = 50
+
+  let dial_out_of_range = "dial out of range"
+
+  (** [next n] is the new state of the dial after turning [Right].
+      Raises: [dial_out_of_range] if [n] is greater than 99. *)
+  let next = function
+    | n when n < 99 ->
+        n + 1
+    | 99 ->
+        0
+    | _ ->
+        failwith dial_out_of_range
+
+  (** [prev n] is the new state of the dial after turning [Left].
+      Raises: [dial_out_of_range] if [n] is less than 0. *)
+  let prev = function
+    | n when n > 0 ->
+        n - 1
+    | 0 ->
+        99
+    | _ ->
+        failwith dial_out_of_range
+
+  (** [turn current direction] is the new state of the dial after turning [direction] from [current].
+      Raises: [dial_out_of_range] if the dial is moved to an invalid state. *)
+  let rec turn current direction =
+    match direction with
+    | Left 0 ->
+        current
+    | Left n ->
+        turn (prev current) (Left (n - 1))
+    | Right 0 ->
+        current
+    | Right n ->
+        turn (next current) (Right (n - 1))
+
+  let to_string = string_of_int
+
+  let to_int t = t
+
+  let pp_direction = function
+    | Left n ->
+        "Left " ^ string_of_int n
+    | Right n ->
+        "Right " ^ string_of_int n
+end
diff --git a/ocaml/lib/domain/d01p02.ml b/ocaml/lib/domain/d01p02.ml
new file mode 100644
index 0000000..f71e965
--- /dev/null
+++ b/ocaml/lib/domain/d01p02.ml
@@ -0,0 +1,95 @@
+module Dial : sig
+  (** [t] is a dial between 0 and 99 inclusive *)
+  type t
+
+  (** [direction] is a direction the dial can be turned *)
+  type direction = Left of int | Right of int
+
+  val start : t
+  (** [start] is the initial state of the dial *)
+
+  val dial_out_of_range : string
+  (** [dial_out_of_range] is the error message when the dial is out of range *)
+
+  val prev : t -> t
+
+  val next : t -> t
+
+  val is_zero : t -> bool
+
+  val to_string : t -> string
+  (** [to_string t] is the string representation of [t] *)
+
+  val to_int : t -> int
+  (** [to_int t] is the integer representation of [t] *)
+
+  val pp_direction : direction -> string
+end = struct
+  (** [t] is an int between 0 and 99 inclusive *)
+  type t = int
+
+  type direction = Left of int | Right of int
+
+  let start = 50
+
+  let dial_out_of_range = "dial out of range"
+
+  (** [next n] is the new state of the dial after turning [Right].
+      Raises: [dial_out_of_range] if [n] is greater than 99. *)
+  let next = function
+    | n when n < 99 ->
+        n + 1
+    | 99 ->
+        0
+    | _ ->
+        failwith dial_out_of_range
+
+  (** [prev n] is the new state of the dial after turning [Left].
+      Raises: [dial_out_of_range] if [n] is less than 0. *)
+  let prev = function
+    | n when n > 0 ->
+        n - 1
+    | 0 ->
+        99
+    | _ ->
+        failwith dial_out_of_range
+
+  let is_zero = function 0 -> true | _ -> false
+
+  let to_string = string_of_int
+
+  let to_int t = t
+
+  let pp_direction = function
+    | Left n ->
+        "Left " ^ string_of_int n
+    | Right n ->
+        "Right " ^ string_of_int n
+end
+
+module Turner : sig
+  val turn : Dial.t -> int -> Dial.direction -> Dial.t * int
+  (** [turn dial direction] is the new state of the dial after turning [direction] on [dial] *)
+end = struct
+  (** [turn dial direction] is the new state of the dial after turning [direction] on [dial].
+      Raises: [dial_out_of_range] if the dial is moved to an invalid state. *)
+  let rec turn dial zero_count direction =
+    let open Dial in
+    match direction with
+    | Left 0 ->
+        (dial, zero_count)
+    | Left n ->
+        let dial' = prev dial in
+        let zero_count' =
+          if Dial.is_zero dial' then zero_count + 1 else zero_count
+        in
+        turn dial' zero_count' (Left (n - 1))
+    | Right 0 ->
+        (dial, zero_count)
+    | Right n ->
+        let dial' = next dial in
+        let zero_count' =
+          if Dial.is_zero dial' then zero_count + 1 else zero_count
+        in
+        turn dial' zero_count' (Right (n - 1))
+end
diff --git a/ocaml/lib/domain/d02p01.ml b/ocaml/lib/domain/d02p01.ml
new file mode 100644
index 0000000..725d4b1
--- /dev/null
+++ b/ocaml/lib/domain/d02p01.ml
@@ -0,0 +1,33 @@
+module ID = struct
+  (** *)
+  type t = int
+
+  let create num = num
+
+  let validate rules id = List.fold_left (fun acc r -> acc && r id) true rules
+
+  let incr = ( + ) 1
+
+  let to_int id = id
+
+  let to_string = string_of_int
+
+  let pp id = "ID=" ^ string_of_int id
+end
+
+module Range = struct
+  type t = ID.t * ID.t
+
+  let create (id1, id2) = (ID.create id1, ID.create id2)
+
+  let rec collect range = collect_range_aux [] range
+
+  and collect_range_aux lst (id1, id2) =
+    match id1 <= id2 with
+    | false ->
+        lst
+    | true ->
+        collect_range_aux (id1 :: lst) (ID.incr id1, id2)
+
+  let pp (id1, id2) = "(L" ^ ID.pp id1 ^ ", R" ^ ID.pp id2 ^ ")"
+end
diff --git a/ocaml/lib/domain/d02p01.mli b/ocaml/lib/domain/d02p01.mli
new file mode 100644
index 0000000..55665fe
--- /dev/null
+++ b/ocaml/lib/domain/d02p01.mli
@@ -0,0 +1,36 @@
+module ID : sig
+  (** [t] is a ID within a range *)
+  type t
+
+  val create : int -> t
+  (** [create num] is an ID [t] *)
+
+  val validate : (t -> bool) list -> t -> bool
+  (** [validate rules id] is [true] if the [id] passes all rule checks *)
+
+  val incr : t -> t
+  (** [incr id] is the next [id] in the sequence *)
+
+  val to_int : t -> int
+  (** [to_int id] is an integer representation of [id] *)
+
+  val to_string : t -> string
+  (** [to_string id] is an string representation of [id] *)
+
+  val pp : t -> string
+  (** [pp id] is a pretty string representing [id] *)
+end
+
+module Range : sig
+  (** [t] is a range of values *)
+  type t
+
+  val create : int * int -> t
+  (** [create (s, e)] is a range starting at [s] and ending at [e]. *)
+
+  val collect : t -> ID.t list
+  (** [collect r] is a list containing all elements within the range (inclusive). *)
+
+  val pp : t -> string
+  (** [pp r] is a pretty string representing [r] *)
+end
diff --git a/ocaml/lib/domain/d02p02.ml b/ocaml/lib/domain/d02p02.ml
new file mode 100644
index 0000000..b2b55f1
--- /dev/null
+++ b/ocaml/lib/domain/d02p02.ml
@@ -0,0 +1,29 @@
+module ID = struct
+  (** *)
+  type t = int
+
+  let create num = num
+
+  let incr = ( + ) 1
+
+  let to_string = string_of_int
+
+  let pp id = "ID=" ^ string_of_int id
+end
+
+module Range = struct
+  type t = ID.t * ID.t
+
+  let create (id1, id2) = (ID.create id1, ID.create id2)
+
+  let rec collect range = collect_range_aux [] range
+
+  and collect_range_aux lst (id1, id2) =
+    match id1 <= id2 with
+    | false ->
+        lst
+    | true ->
+        collect_range_aux (id1 :: lst) (ID.incr id1, id2)
+
+  let pp (id1, id2) = "(L" ^ ID.pp id1 ^ ", R" ^ ID.pp id2 ^ ")"
+end
diff --git a/ocaml/lib/domain/d02p02.mli b/ocaml/lib/domain/d02p02.mli
new file mode 100644
index 0000000..f918ae1
--- /dev/null
+++ b/ocaml/lib/domain/d02p02.mli
@@ -0,0 +1,30 @@
+module ID : sig
+  (** [t] is a ID within a range *)
+  type t
+
+  val create : int -> t
+  (** [create num] is an ID [t] *)
+
+  val incr : t -> t
+  (** [incr id] is the next [id] in the sequence *)
+
+  val to_string : t -> string
+  (** [to_string id] is an string representation of [id] *)
+
+  val pp : t -> string
+  (** [pp id] is a pretty string representing [id] *)
+end
+
+module Range : sig
+  (** [t] is a range of values *)
+  type t
+
+  val create : int * int -> t
+  (** [create (s, e)] is a range starting at [s] and ending at [e]. *)
+
+  val collect : t -> ID.t list
+  (** [collect r] is a list containing all elements within the range (inclusive). *)
+
+  val pp : t -> string
+  (** [pp r] is a pretty string representing [r] *)
+end
diff --git a/ocaml/lib/domain/d03p01.ml b/ocaml/lib/domain/d03p01.ml
new file mode 100644
index 0000000..1367712
--- /dev/null
+++ b/ocaml/lib/domain/d03p01.ml
@@ -0,0 +1,114 @@
+module Battery : sig
+  type t
+
+  val of_int : int -> t
+
+  val to_int : t -> int
+
+  val to_string : t -> string
+
+  val compare : t -> t -> int
+
+  val pp : t -> string
+end = struct
+  type t = int
+
+  let of_int i = i
+
+  let to_int b = b
+
+  let to_string = string_of_int
+
+  let compare = Int.compare
+
+  let pp = string_of_int
+end
+
+module BatteryBank : sig
+  type t
+
+  val highest_joltage : t -> int
+  (** [highest_joltage bb] is an integer created from the two highest
+      digits in [bb].
+      Raises: [Assert_failure] if [bb] is empty. *)
+
+  val of_string : string -> t
+
+  val of_list : Battery.t list -> t
+
+  val to_list : t -> Battery.t list
+
+  val pp : t -> string
+end = struct
+  type t = Battery.t list
+
+  let rec highest_joltage bb =
+    assert (List.length bb > 0) ;
+    match highest_joltage_aux (None, None) bb with
+    | None, None ->
+        0
+    | Some x, Some y ->
+        int_of_string (Battery.to_string x ^ Battery.to_string y)
+    | _ ->
+        failwith "highest_joltage must be two digits"
+
+  and highest_joltage_aux acc = function
+    | [] ->
+        acc
+    | [elt] -> (
+      match acc with
+      | None, None ->
+          (Some (Battery.of_int 0), Some elt)
+      | Some first, None ->
+          (Some first, Some elt)
+      | None, Some second ->
+          (Some second, Some elt)
+      | Some first, Some second ->
+          if elt > second then (Some first, Some elt)
+          else (Some first, Some second) )
+    | h :: t ->
+        highest_joltage_aux
+          ( match acc with
+          | None, None ->
+              (Some h, None)
+          | Some first, None ->
+              let second = Battery.of_int 0 in
+              swap_if_higher first second h
+          | Some first, Some second ->
+              swap_if_higher first second h
+          | _ ->
+              failwith "this branch should be impossible" )
+          t
+
+  and swap_if_higher first second considering =
+    assert (first >= second) ;
+    let c_gt_f = Battery.compare considering first = 1 in
+    let c_gt_s = Battery.compare considering second = 1 in
+    match (c_gt_f, c_gt_s) with
+    | true, true ->
+        (Some considering, None)
+    | false, true ->
+        (Some first, Some considering)
+    | true, false ->
+        failwith "[second] should never be greater than [first]"
+    | false, false ->
+        (Some first, Some second)
+
+  let of_string s =
+    s |> String.to_seq
+    |> Seq.map (fun c -> Char.escaped c |> int_of_string |> Battery.of_int)
+    |> List.of_seq
+
+  let of_list lst = lst
+
+  let to_list bb = bb
+
+  let pp bb =
+    "[ "
+    ^ ( bb |> List.map Battery.pp
+      |> List.fold_left
+           (fun acc b ->
+             if acc = "" then b ^ ";" else Printf.sprintf "%s %s;" acc b )
+           "" )
+    ^ " ]"
+end
diff --git a/ocaml/lib/domain/d03p02.ml b/ocaml/lib/domain/d03p02.ml
new file mode 100644
index 0000000..88257d0
--- /dev/null
+++ b/ocaml/lib/domain/d03p02.ml
@@ -0,0 +1,116 @@
+module Battery : sig
+  type t
+
+  val of_int : int -> t
+
+  val to_int : t -> int
+
+  val to_string : t -> string
+
+  val compare : t -> t -> int
+
+  val pp : t -> string
+end = struct
+  type t = int
+
+  let of_int i = i
+
+  let to_int b = b
+
+  let to_string = string_of_int
+
+  let compare = Int.compare
+
+  let pp = string_of_int
+end
+
+module BatteryBank : sig
+  type t
+
+  val highest_joltage : t -> int
+  (** [highest_joltage bb] is an integer created from the two highest
+      digits in [bb].
+      Raises: [Assert_failure] if [bb] is empty. *)
+
+  val of_string : string -> t
+
+  val of_list : Battery.t list -> t
+
+  val to_list : t -> Battery.t list
+
+  val pp : t -> string
+end = struct
+  type t = Battery.t list
+
+  type highest = {one: Battery.t option; two: Battery.t option}
+
+  let rec highest_joltage bb =
+    assert (List.length bb > 0) ;
+    match highest_joltage_aux {one= None; two= None} bb with
+    | {one= None; two= None} ->
+        0
+    | {one= Some x; two= Some y} ->
+        int_of_string (Battery.to_string x ^ Battery.to_string y)
+    | _ ->
+        failwith "highest_joltage must be two digits"
+
+  and highest_joltage_aux acc = function
+    | [] ->
+        acc
+    | [elt] -> (
+      match acc with
+      | {one= None; two= None} ->
+          {one= Some (Battery.of_int 0); two= Some elt}
+      | {one= Some first; two= None} ->
+          {one= Some first; two= Some elt}
+      | {one= None; two= Some second} ->
+          {one= Some second; two= Some elt}
+      | {one= Some first; two= Some second} ->
+          if elt > second then {one= Some first; two= Some elt}
+          else {one= Some first; two= Some second} )
+    | h :: t ->
+        highest_joltage_aux
+          ( match acc with
+          | {one= None; two= None} ->
+              {one= Some h; two= None}
+          | {one= Some first; two= None} ->
+              let second = Battery.of_int 0 in
+              swap_if_higher first second h
+          | {one= Some first; two= Some second} ->
+              swap_if_higher first second h
+          | _ ->
+              failwith "this branch should be impossible" )
+          t
+
+  and swap_if_higher first second considering =
+    assert (first >= second) ;
+    let c_gt_f = Battery.compare considering first = 1 in
+    let c_gt_s = Battery.compare considering second = 1 in
+    match (c_gt_f, c_gt_s) with
+    | true, true ->
+        {one= Some considering; two= None}
+    | false, true ->
+        {one= Some first; two= Some considering}
+    | true, false ->
+        failwith "[second] should never be greater than [first]"
+    | false, false ->
+        {one= Some first; two= Some second}
+
+  let of_string s =
+    s |> String.to_seq
+    |> Seq.map (fun c -> Char.escaped c |> int_of_string |> Battery.of_int)
+    |> List.of_seq
+
+  let of_list lst = lst
+
+  let to_list bb = bb
+
+  let pp bb =
+    "[ "
+    ^ ( bb |> List.map Battery.pp
+      |> List.fold_left
+           (fun acc b ->
+             if acc = "" then b ^ ";" else Printf.sprintf "%s %s;" acc b )
+           "" )
+    ^ " ]"
+end
diff --git a/ocaml/lib/domain/dune b/ocaml/lib/domain/dune
new file mode 100644
index 0000000..5b13d31
--- /dev/null
+++ b/ocaml/lib/domain/dune
@@ -0,0 +1,13 @@
+(library
+  (name domain)
+  (inline_tests)
+  (libraries
+    fmt
+    logs)
+  (preprocess
+    (pps
+      ppx_deriving.show
+      ppx_deriving.eq
+      ppx_deriving.ord
+      ppx_inline_test
+      ppx_expect)))
diff --git a/ocaml/lib/domain/matrix.ml b/ocaml/lib/domain/matrix.ml
new file mode 100644
index 0000000..fdf476f
--- /dev/null
+++ b/ocaml/lib/domain/matrix.ml
@@ -0,0 +1,196 @@
+module M : sig
+  type 'a t = 'a array array
+
+  val empty : int -> int -> 'a -> 'a t
+  (** [empty rows columns initial] is an empty 2D array of size [rows] * [columns]
+      where each element in the array is initialized to [initial]. *)
+
+  val of_list : 'a list list -> 'a t
+  (** [of_list lst] is a 2D array where every element in the array is an
+      element corresponds to an element of the [lst]. *)
+
+  val to_list : 'a t -> 'a list list
+  (** [to_list matrix] is a 2D list where every element in the list is an
+      element corresponds to an element of the [matrix]. *)
+
+  val of_string : string -> string t
+  (** [of_string str] is a 2D array where every character is an element. *)
+
+  val get : 'a t -> int -> int -> 'a
+  (** [get matrix x y] is an alias for [matrix.(y).(x)].
+      Requires: [x] and [y] are positive integers or 0. *)
+
+  val set : 'a t -> int -> int -> 'a -> unit
+  (** [set matrix x y v] is an alias for [matrix.(y).(x) <- v].
+      Requires: [x] and [y] are positive integers or 0. *)
+
+  val get_valid_neighbours : 'a t -> int -> int -> (int * int) list
+  (** [get_valid_neighbours matrix x y] is a list of pairs in the format
+      (x * y) that represent the valid surrounding positions of [matrix.(y).(x)].
+      Requires: [x] and [y] are positive integers or 0. *)
+
+  val pp : ('a -> string) -> 'a t -> string
+  (** [pp matrix string_of_elt] is the string representation of the [matrix]
+      where [string_of_elt] is called on each element. *)
+end = struct
+  type 'a t = 'a array array
+
+  let empty cols rows initial = Array.make_matrix cols rows initial
+
+  let of_list lst = Array.of_list @@ List.map Array.of_list lst
+
+  let to_list matrix = Array.to_list @@ Array.map Array.to_list matrix
+
+  let of_string str =
+    let lines =
+      str |> String.split_on_char '\n'
+      |> List.filter_map (fun line ->
+          let trimmed = String.trim line in
+          if trimmed <> "" then Some trimmed else None )
+    in
+    let char_lst =
+      List.map
+        (fun s -> s |> String.to_seq |> List.of_seq |> List.map Char.escaped)
+        lines
+    in
+    of_list char_lst
+
+  let get matrix x y = matrix.(y).(x)
+
+  let set matrix x y v = matrix.(y).(x) <- v
+
+  let get_valid_neighbours matrix x y =
+    let potential_neighbours =
+      [ (x - 1, y - 1)
+      ; (x, y - 1)
+      ; (x + 1, y - 1)
+      ; (x - 1, y)
+      ; (x + 1, y)
+      ; (x - 1, y + 1)
+      ; (x, y + 1)
+      ; (x + 1, y + 1) ]
+    in
+    let min_x = 0 in
+    let max_x = Array.length matrix.(y) - 1 in
+    let min_y = 0 in
+    let max_y = Array.length matrix - 1 in
+    List.filter
+      (fun (x, y) -> min_x <= x && x <= max_x && min_y <= y && y <= max_y)
+      potential_neighbours
+
+  let pp string_of_elt matrix =
+    "["
+    ^ Array.fold_left
+        (fun col_acc arr ->
+          let row =
+            "["
+            ^ Array.fold_left
+                (fun row_acc elt -> row_acc ^ string_of_elt elt ^ "; ")
+                " " arr
+            ^ "]"
+          in
+          col_acc ^ "  " ^ row ^ "\n" )
+        "\n" matrix
+    ^ "]"
+end
+
+let%expect_test "matrix created from input is pretty-printed as the same matrix"
+    =
+  let example =
+    {|..@@.@@@@.
+@@@.@.@.@@
+@@@@@.@.@@
+@.@@@@..@.
+@@.@@@@.@@
+.@@@@@@@.@
+.@.@.@.@@@
+@.@@@.@@@@
+.@@@@@@@@.
+@.@.@@@.@.|}
+  in
+  print_string @@ M.pp (fun s -> s) @@ M.of_string example ;
+  [%expect
+    {|
+    [
+      [ .; .; @; @; .; @; @; @; @; .; ]
+      [ @; @; @; .; @; .; @; .; @; @; ]
+      [ @; @; @; @; @; .; @; .; @; @; ]
+      [ @; .; @; @; @; @; .; .; @; .; ]
+      [ @; @; .; @; @; @; @; .; @; @; ]
+      [ .; @; @; @; @; @; @; @; .; @; ]
+      [ .; @; .; @; .; @; .; @; @; @; ]
+      [ @; .; @; @; @; .; @; @; @; @; ]
+      [ .; @; @; @; @; @; @; @; @; .; ]
+      [ @; .; @; .; @; @; @; .; @; .; ]
+    ]
+    |}]
+
+let%expect_test "direct access of the matrix is in form matrix.(y).(x)" =
+  let example =
+    {|..@@.@@@@.
+@@@.@.@.@@
+@@@@@.@.@@
+@.@@@@..@.
+@@.@@@@.@@
+.@@@@@@@.@
+.@.@.@.@@@
+@.@@@.@@@@
+.@@@@@@@@.
+@.@.@@@.@.|}
+  in
+  let matrix = M.of_string example in
+  print_string matrix.(0).(0) ;
+  [%expect "."] ;
+  print_string matrix.(0).(1) ;
+  [%expect "."] ;
+  print_string matrix.(0).(2) ;
+  [%expect "@"] ;
+  print_string matrix.(0).(3) ;
+  [%expect "@"] ;
+  print_string matrix.(0).(4) ;
+  [%expect "."] ;
+  print_string matrix.(0).(5) ;
+  [%expect "@"] ;
+  print_string matrix.(0).(6) ;
+  [%expect "@"] ;
+  print_string matrix.(0).(7) ;
+  [%expect "@"] ;
+  print_string matrix.(0).(8) ;
+  [%expect "@"] ;
+  print_string matrix.(0).(9) ;
+  [%expect "."]
+
+let%expect_test "[M.get matrix x y] is an alias for [matrix.(y).(x)]" =
+  let example =
+    {|..@@.@@@@.
+@@@.@.@.@@
+@@@@@.@.@@
+@.@@@@..@.
+@@.@@@@.@@
+.@@@@@@@.@
+.@.@.@.@@@
+@.@@@.@@@@
+.@@@@@@@@.
+@.@.@@@.@.|}
+  in
+  let matrix = M.of_string example in
+  print_string @@ M.get matrix 0 0 ;
+  [%expect "."] ;
+  print_string @@ M.get matrix 1 0 ;
+  [%expect "."] ;
+  print_string @@ M.get matrix 2 0 ;
+  [%expect "@"] ;
+  print_string @@ M.get matrix 3 0 ;
+  [%expect "@"] ;
+  print_string @@ M.get matrix 4 0 ;
+  [%expect "."] ;
+  print_string @@ M.get matrix 5 0 ;
+  [%expect "@"] ;
+  print_string @@ M.get matrix 6 0 ;
+  [%expect "@"] ;
+  print_string @@ M.get matrix 7 0 ;
+  [%expect "@"] ;
+  print_string @@ M.get matrix 8 0 ;
+  [%expect "@"] ;
+  print_string @@ M.get matrix 9 0 ;
+  [%expect "."]
diff --git a/ocaml/lib/domain/range.ml b/ocaml/lib/domain/range.ml
new file mode 100644
index 0000000..a1bdc00
--- /dev/null
+++ b/ocaml/lib/domain/range.ml
@@ -0,0 +1,67 @@
+module M : sig
+  type t
+
+  val of_string : string -> t option
+  (** [of_string s] is a range of integers if [s] is a string in the form ["%d-%d"]
+      or [None] otherwise. *)
+
+  val collect : t -> int list
+  (** [collect range] is a fully realised range as a list.
+      Example: ["1-5" |> of_string |> collect] is the list [\[1;2;3;4;5\]].
+      Example: ["5-1" |> of_string |> collect] is the list [\[5;4;3;2;1\]].*)
+
+  val pp : t -> string
+  (** [pp range] is a pretty-printed version of the range. *)
+end = struct
+  type t = int * int
+
+  let of_string s =
+    Scanf.sscanf_opt s "%d-%d" (fun start finish -> (start, finish))
+
+  let rec collect (start, finish) =
+    let collected =
+      match Int.compare start finish with
+      | -1 ->
+          collect_range_aux Int.succ ( > ) [] (start, finish)
+      | 0 ->
+          [start]
+      | 1 ->
+          collect_range_aux Int.pred ( < ) [] (start, finish)
+      | _ ->
+          assert false
+    in
+    List.rev collected
+
+  and collect_range_aux fn cmp lst (start, finish) =
+    if cmp start finish then lst
+    else collect_range_aux fn cmp (start :: lst) (fn start, finish)
+
+  let pp (start, finish) = string_of_int start ^ "-" ^ string_of_int finish
+end
+
+let%expect_test "incrementing range" =
+  match M.of_string "1-5" with
+  | None ->
+      [%expect.unreachable]
+  | Some range ->
+      let collected = M.collect range in
+      List.iter print_int collected ;
+      [%expect "12345"]
+
+let%expect_test "decrementing range" =
+  match M.of_string "5-1" with
+  | None ->
+      [%expect.unreachable]
+  | Some range ->
+      let collected = M.collect range in
+      List.iter print_int collected ;
+      [%expect "54321"]
+
+let%expect_test "one element range" =
+  match M.of_string "1-1" with
+  | None ->
+      [%expect.unreachable]
+  | Some range ->
+      let collected = M.collect range in
+      List.iter print_int collected ;
+      [%expect "1"]
diff --git a/ocaml/lib/infrastructure/dune b/ocaml/lib/infrastructure/dune
new file mode 100644
index 0000000..b9d250f
--- /dev/null
+++ b/ocaml/lib/infrastructure/dune
@@ -0,0 +1,15 @@
+(library
+  (name infrastructure)
+  (libraries
+    application
+    domain
+    fmt
+    logs)
+  (inline_tests)
+  (preprocess
+    (pps
+      ppx_deriving.show
+      ppx_deriving.eq
+      ppx_deriving.ord
+      ppx_inline_test
+      ppx_expect)))
diff --git a/ocaml/lib/infrastructure/file.ml b/ocaml/lib/infrastructure/file.ml
new file mode 100644
index 0000000..3b49c01
--- /dev/null
+++ b/ocaml/lib/infrastructure/file.ml
@@ -0,0 +1,4 @@
+let read filename =
+  let chan = In_channel.open_text filename in
+  let content = In_channel.input_all chan in
+  In_channel.close chan ; content
diff --git a/ocaml/lib/infrastructure/file.mli b/ocaml/lib/infrastructure/file.mli
new file mode 100644
index 0000000..17d4495
--- /dev/null
+++ b/ocaml/lib/infrastructure/file.mli
@@ -0,0 +1,3 @@
+val read : string -> string
+(** [read filename] is the contents of [filename] as a string.
+    The empty string is returned if [filename] does not exist. *)
diff --git a/ocaml/lib/presentation/cli.ml b/ocaml/lib/presentation/cli.ml
new file mode 100644
index 0000000..7864e7f
--- /dev/null
+++ b/ocaml/lib/presentation/cli.ml
@@ -0,0 +1,62 @@
+(* Business logic behind CLI *)
+
+let run_solver name solver filepath =
+  let content = Infrastructure.File.read filepath in
+  match solver content () with
+  | Error msg ->
+      Logs.app (fun m -> m "[%s] Err=%s" name msg)
+  | Ok answer ->
+      Logs.app (fun m -> m "[%s] ANSWER=%d" name answer)
+
+let run_day _ = function
+  | 1 ->
+      let filepath = "../_input/day_01.txt" in
+      run_solver "D01P01" Application.D01p01.solve filepath ;
+      run_solver "D01P02" Application.D01p02.solve filepath ;
+      0
+  | 2 ->
+      let filepath = "../_input/day_02.txt" in
+      run_solver "D02P01" Application.D02p01.solve filepath ;
+      run_solver "D02P02" Application.D02p02.solve filepath ;
+      0
+  | 3 ->
+      let filepath = "../_input/day_03.txt" in
+      run_solver "D03P01" Application.D03p01.solve filepath ;
+      run_solver "D03P02" Application.D03p02.solve filepath ;
+      0
+  | 4 ->
+      let filepath = "../_input/day_04.txt" in
+      run_solver "D04P01" Application.D04p01.solve filepath ;
+      run_solver "D04P02" Application.D04p02.solve filepath ;
+      0
+  | 5 ->
+      let filepath = "../_input/day_05.txt" in
+      run_solver "D05P01" Application.D05p01.solve filepath ;
+      0
+  | 6 ->
+      let filepath = "../_input/day_06.txt" in
+      run_solver "D06P01" Application.D06p01.solve filepath ;
+      run_solver "D06P02" Application.D06p02.solve filepath ;
+      0
+  | _ ->
+      failwith "day not implemented"
+
+(* Command line interface *)
+
+open Cmdliner
+
+let setup_log style_renderer = Fmt_tty.setup_std_outputs ?style_renderer ()
+
+let setup_log_t = Term.(const setup_log $ Fmt_cli.style_renderer ())
+
+let day_arg =
+  let doc = "Day to run. MUST be in range of 1-12." in
+  Arg.(value & pos 0 int 1 & info [] ~docv:"DAY" ~doc)
+
+let day_t = Term.(const run_day $ setup_log_t $ day_arg)
+
+let cmd =
+  let info = Cmd.info "aoc" ~version:"0.1.0" in
+  Cmd.v info day_t
+
+let run () = Cmd.eval' cmd
diff --git a/ocaml/lib/presentation/dune b/ocaml/lib/presentation/dune
new file mode 100644
index 0000000..ae1fcb1
--- /dev/null
+++ b/ocaml/lib/presentation/dune
@@ -0,0 +1,16 @@
+(library
+  (name presentation)
+  (libraries
+    application
+    domain
+    infrastructure
+    cmdliner
+    fmt.cli
+    fmt.tty)
+  (inline_tests)
+  (preprocess
+    (pps
+      ppx_deriving.show
+      ppx_deriving.eq
+      ppx_deriving.ord
+      ppx_expect)))
diff --git a/ocaml/test/application/dune b/ocaml/test/application/dune
new file mode 100644
index 0000000..7a90f81
--- /dev/null
+++ b/ocaml/test/application/dune
@@ -0,0 +1,9 @@
+(tests
+ (names
+   test_d01p01
+   test_d01p02
+   test_d04p01)
+ (libraries
+   application
+   domain
+   alcotest))
diff --git a/ocaml/test/application/test_d01p01.ml b/ocaml/test/application/test_d01p01.ml
new file mode 100644
index 0000000..e57db01
--- /dev/null
+++ b/ocaml/test/application/test_d01p01.ml
@@ -0,0 +1,23 @@
+open Application.D01p01
+
+let example_data = {|L68
+L30
+R48
+L5
+R60
+L55
+L1
+L99
+R14
+L82|}
+
+let test_full_given_example () =
+  Alcotest.(check int)
+    "full given example" 3
+    (match solve example_data () with Error _ -> 0 | Ok ans -> ans)
+
+let () =
+  let open Alcotest in
+  run "D01p01"
+    [ ( "given-example"
+      , [test_case "full given example" `Quick test_full_given_example] ) ]
diff --git a/ocaml/test/application/test_d01p02.ml b/ocaml/test/application/test_d01p02.ml
new file mode 100644
index 0000000..bbda035
--- /dev/null
+++ b/ocaml/test/application/test_d01p02.ml
@@ -0,0 +1,23 @@
+open Application.D01p02
+
+let example_data = {|L68
+L30
+R48
+L5
+R60
+L55
+L1
+L99
+R14
+L82|}
+
+let test_full_given_example () =
+  Alcotest.(check int)
+    "full given example" 6
+    (match solve example_data () with Error _ -> 0 | Ok ans -> ans)
+
+let () =
+  let open Alcotest in
+  run "D01p02"
+    [ ( "given-example"
+      , [test_case "full given example" `Quick test_full_given_example] ) ]
diff --git a/ocaml/test/application/test_d04p01.ml b/ocaml/test/application/test_d04p01.ml
new file mode 100644
index 0000000..ffbe102
--- /dev/null
+++ b/ocaml/test/application/test_d04p01.ml
@@ -0,0 +1,24 @@
+open Application.D04p01
+
+let example =
+  {|..@@.@@@@.
+@@@.@.@.@@
+@@@@@.@.@@
+@.@@@@..@.
+@@.@@@@.@@
+.@@@@@@@.@
+.@.@.@.@@@
+@.@@@.@@@@
+.@@@@@@@@.
+@.@.@@@.@.|}
+
+let test_input_to_matrix have want () =
+  Alcotest.(check int) "number of rolls of paper that are accessible" want
+  @@ match solve have () with Error _ -> 0 | Ok ans -> ans
+
+let () =
+  let open Alcotest in
+  run "D04p01"
+    [ ( "given-example"
+      , [test_case "full example" `Quick @@ test_input_to_matrix example 13] )
+    ]
diff --git a/ocaml/test/domain/dune b/ocaml/test/domain/dune
new file mode 100644
index 0000000..1364288
--- /dev/null
+++ b/ocaml/test/domain/dune
@@ -0,0 +1,11 @@
+(tests
+ (names
+   test_d01p01
+   test_d01p02
+   test_d03p01)
+ (libraries
+   domain
+   alcotest
+   qcheck-core
+   qcheck-alcotest)
+ (modes byte exe))
diff --git a/ocaml/test/domain/test_d01p01.ml b/ocaml/test/domain/test_d01p01.ml
new file mode 100644
index 0000000..23404f6
--- /dev/null
+++ b/ocaml/test/domain/test_d01p01.ml
@@ -0,0 +1,29 @@
+open Domain.D01p01
+
+let test_start () =
+  Alcotest.(check int) "incorrect starting state" 50 (Dial.to_int Dial.start)
+
+let test_turn desc exp dir =
+  Alcotest.(check int) desc exp (Dial.to_int (Dial.turn Dial.start dir))
+
+let test_turn_left_one () =
+  test_turn "incorrect result when turning left one step" 49 (Dial.Left 1)
+
+let test_turn_left_100 () =
+  test_turn "incorrect result when turning left 100 steps" 50 (Dial.Left 100)
+
+let test_turn_right_one () =
+  test_turn "incorrect result when turning right one step" 51 (Dial.Right 1)
+
+let test_turn_right_100 () =
+  test_turn "incorrect result when turning right 100 steps" 50 (Dial.Right 100)
+
+let () =
+  let open Alcotest in
+  run "D01p01"
+    [ ("initial-state", [test_case "starting state" `Quick test_start])
+    ; ( "turning-dial"
+      , [ test_case "turning left one step" `Quick test_turn_left_one
+        ; test_case "turning right one step" `Quick test_turn_right_one
+        ; test_case "turning left 100 steps" `Quick test_turn_left_100
+        ; test_case "turning right 100 steps" `Quick test_turn_right_100 ] ) ]
diff --git a/ocaml/test/domain/test_d01p02.ml b/ocaml/test/domain/test_d01p02.ml
new file mode 100644
index 0000000..98c06c3
--- /dev/null
+++ b/ocaml/test/domain/test_d01p02.ml
@@ -0,0 +1,41 @@
+open Domain.D01p02
+
+let test_start () =
+  Alcotest.(check int) "incorrect starting state" 50 (Dial.to_int Dial.start)
+
+let test_turn errmsg exp dir =
+  Alcotest.(check int)
+    errmsg exp
+    (Dial.to_int (fst (Turner.turn Dial.start 0 dir)))
+
+let test_turn_left_one () =
+  test_turn "incorrect result when turning left one step" 49 (Dial.Left 1)
+
+let test_turn_left_100 () =
+  test_turn "incorrect result when turning left 100 steps" 50 (Dial.Left 100)
+
+let test_turn_right_one () =
+  test_turn "incorrect result when turning right one step" 51 (Dial.Right 1)
+
+let test_turn_right_100 () =
+  test_turn "incorrect result when turning right 100 steps" 50 (Dial.Right 100)
+
+let test_zero_count errmsg exp dir =
+  Alcotest.(check int) errmsg exp (snd (Turner.turn Dial.start 0 dir))
+
+let test_zero_count_right_1000 () =
+  test_zero_count "zero MUST be counted each time it is passed" 10
+    (Dial.Right 1000)
+
+let () =
+  let open Alcotest in
+  run "D01p02"
+    [ ("initial-state", [test_case "starting state" `Quick test_start])
+    ; ( "turning-dial-regression"
+      , [ test_case "turning left one step" `Quick test_turn_left_one
+        ; test_case "turning right one step" `Quick test_turn_right_one
+        ; test_case "turning left 100 steps" `Quick test_turn_left_100
+        ; test_case "turning right 100 steps" `Quick test_turn_right_100 ] )
+    ; ( "zero-count"
+      , [ test_case "zero count after turning right 1000 steps" `Quick
+            test_zero_count_right_1000 ] ) ]
diff --git a/ocaml/test/domain/test_d03p01.ml b/ocaml/test/domain/test_d03p01.ml
new file mode 100644
index 0000000..6a2b3cf
--- /dev/null
+++ b/ocaml/test/domain/test_d03p01.ml
@@ -0,0 +1,857 @@
+open Domain.D03p01
+
+let test_highest_joltage have want () =
+  Alcotest.(check int)
+    "highest joltage in battery bank" want
+    (BatteryBank.of_string have |> BatteryBank.highest_joltage)
+
+let largest_digit_always_in_highest_joltage =
+  QCheck2.Test.make ~count:1000
+    ~name:"highest joltage always has contains the largest digit"
+    ~print:(fun s -> s)
+    QCheck2.Gen.(string_of @@ char_range '1' '9')
+    (fun have ->
+      QCheck2.assume (String.length have > 2) ;
+      let got = BatteryBank.of_string have |> BatteryBank.highest_joltage in
+      let first = got / 10 and second = got mod 10 in
+      let want =
+        String.fold_left
+          (fun acc chr -> if acc < chr then chr else acc)
+          '0' have
+        |> Char.escaped |> int_of_string
+      in
+      first = want || second = want )
+
+let () =
+  let open Alcotest in
+  run "D03p01"
+    [ ( "example BatteryBank.highest_joltage"
+      , [ test_case "example line 1" `Quick
+            (test_highest_joltage "987654321111111" 98)
+        ; test_case "example line 2" `Quick
+            (test_highest_joltage "811111111111119" 89)
+        ; test_case "example line 3" `Quick
+            (test_highest_joltage "234234234234278" 78)
+        ; test_case "example line 4" `Quick
+            (test_highest_joltage "818181911112111" 92) ] )
+    ; ( "real BatteryBank.highest_joltage"
+      , [ test_case "real line 001" `Quick
+            (test_highest_joltage
+               "3434845634454364546334335333448443354324533545443235414334477424442444346844344244444434445333344314"
+               88 )
+        ; test_case "real line 002" `Quick
+            (test_highest_joltage
+               "4644333464433434855275434364342435544972433324444444432243354936362863356444434344443333433425344432"
+               99 )
+        ; test_case "real line 003" `Quick
+            (test_highest_joltage
+               "3475855376536553445244645449948436834663673457444335454425154463544745554434526565475244677445573464"
+               99 )
+        ; test_case "real line 004" `Quick
+            (test_highest_joltage
+               "2281212713222421222222213222212222221223122222212125222722232132222251212212322222222722312232333312"
+               87 )
+        ; test_case "real line 005" `Quick
+            (test_highest_joltage
+               "4483335423223456243275328893923136663523559445363393353333233337733323263852953335475336578422333454"
+               99 )
+        ; test_case "real line 006" `Quick
+            (test_highest_joltage
+               "3242323333312323243333333353413314243333232242233323431332332353323333353333333332443515323433322274"
+               74 )
+        ; test_case "real line 007" `Quick
+            (test_highest_joltage
+               "2333332242424335244422323333113323312234133433323243344324444233324245126142444324422445113241224322"
+               65 )
+        ; test_case "real line 008" `Quick
+            (test_highest_joltage
+               "5154432634655462574764324542474445554653643456344345657233718556457665426344257554246426445655364424"
+               87 )
+        ; test_case "real line 009" `Quick
+            (test_highest_joltage
+               "2333128322322632533324333135293331312321323332214333232434433322473232223344341214372234132223223343"
+               97 )
+        ; test_case "real line 010" `Quick
+            (test_highest_joltage
+               "4334244423552542164444513547496574512523344184674374558444434436645643164524326453333335444434455453"
+               98 )
+        ; test_case "real line 011" `Quick
+            (test_highest_joltage
+               "4132222247423242222232632242222124423421222271231244222212222222554221311221262314222222224253442337"
+               77 )
+        ; test_case "real line 012" `Quick
+            (test_highest_joltage
+               "2224322221122233225272222222442223222222271115422222121223262743222224222322422224123122262323222821"
+               82 )
+        ; test_case "real line 013" `Quick
+            (test_highest_joltage
+               "6723822256923221233223334322457233343332383332523433343323228646232524535432233323314353333227243323"
+               98 )
+        ; test_case "real line 014" `Quick
+            (test_highest_joltage
+               "6115546238253222343552462122324244122555232412242231255242342542222232432524132213523232121212324545"
+               86 )
+        ; test_case "real line 015" `Quick
+            (test_highest_joltage
+               "6463573733747321131532311243414374652372276761664731354417577566137677557472577677776125327145332589"
+               89 )
+        ; test_case "real line 016" `Quick
+            (test_highest_joltage
+               "3754415413732333338423242374334432153868351274433435343563444545253375644356474264434423432633233432"
+               88 )
+        ; test_case "real line 017" `Quick
+            (test_highest_joltage
+               "5444434434444444443644344444454454451442423444454444444344443433464444435453445443443354555334454454"
+               66 )
+        ; test_case "real line 018" `Quick
+            (test_highest_joltage
+               "2322232322322342121231422323212136222323332232223332423222231222323222323213211222124112122223323222"
+               64 )
+        ; test_case "real line 019" `Quick
+            (test_highest_joltage
+               "2123222121233313232324221212131322222312114122122222223331524242222223522421122132314232232221325212"
+               55 )
+        ; test_case "real line 020" `Quick
+            (test_highest_joltage
+               "4395244125441654554734234542525455274423553314354552543244444237453434822334223553453354325435235232"
+               98 )
+        ; test_case "real line 021" `Quick
+            (test_highest_joltage
+               "2253424214422444223313135223232832334333553541324423242333333332422343235234313221222522523223223324"
+               85 )
+        ; test_case "real line 022" `Quick
+            (test_highest_joltage
+               "5235226542352363765362222242266353124241222253326335131251514362226422434463674353246334124656282122"
+               82 )
+        ; test_case "real line 023" `Quick
+            (test_highest_joltage
+               "2232123624442243412224246433221223412221211333362434222314122321222374432142634122244234226424224222"
+               76 )
+        ; test_case "real line 024" `Quick
+            (test_highest_joltage
+               "3422335122727323322362432313322322322223332332223816131326233213327243223323343212331236353226232321"
+               87 )
+        ; test_case "real line 025" `Quick
+            (test_highest_joltage
+               "4331335233332333423433313313173432431333333532233333433343363343333332336433333237323332253433443333"
+               77 )
+        ; test_case "real line 026" `Quick
+            (test_highest_joltage
+               "4447448444443444434444443243543534134744452133424233431341466844433346243413344384231154343384832444"
+               88 )
+        ; test_case "real line 027" `Quick
+            (test_highest_joltage
+               "2425565264165457455876521452237584855214342125728464762555858525255422733375855552537425835156285135"
+               88 )
+        ; test_case "real line 028" `Quick
+            (test_highest_joltage
+               "1331226211234222222312211322123232233513242526221423223222232214322223122232333222282842423352327112"
+               88 )
+        ; test_case "real line 029" `Quick
+            (test_highest_joltage
+               "3223434225632352425252225227722722534655252243423421222422525141365526221342142264132653472224125223"
+               77 )
+        ; test_case "real line 030" `Quick
+            (test_highest_joltage
+               "6737524344344356458523434443443144444264443348734644444644541613334445654733443544253434843553348938"
+               98 )
+        ; test_case "real line 031" `Quick
+            (test_highest_joltage
+               "3354422734545554524252254222935229552422513243152263456254352212241422142433745251122447413225375454"
+               99 )
+        ; test_case "real line 032" `Quick
+            (test_highest_joltage
+               "2264222763222232222612274362233123232631142294332533623322433223214212132333126222163271553323113546"
+               97 )
+        ; test_case "real line 033" `Quick
+            (test_highest_joltage
+               "3224455231554212335327234452322334222224355323335331221333422324235123435122325533513215236323223567"
+               77 )
+        ; test_case "real line 034" `Quick
+            (test_highest_joltage
+               "3364433535332344433338434131353453131351342344343443434434354345544614344346424444464434454542463163"
+               86 )
+        ; test_case "real line 035" `Quick
+            (test_highest_joltage
+               "3334311333353143563633334222343222333252653351532534233523263233265333333263352353553235353353353333"
+               66 )
+        ; test_case "real line 036" `Quick
+            (test_highest_joltage
+               "2341414245234322423322241415434452323345544444442373441644233534541453435433235452441251543332443224"
+               76 )
+        ; test_case "real line 037" `Quick
+            (test_highest_joltage
+               "2334222122362114522212222223212342234225232414234232252812322221321123236322322233153222246262451321"
+               86 )
+        ; test_case "real line 038" `Quick
+            (test_highest_joltage
+               "3222213324143222521232511323442333353115354312453322323233245125121212335352213422325232423442113222"
+               55 )
+        ; test_case "real line 039" `Quick
+            (test_highest_joltage
+               "4242234421454245624314342344231425552454131112356244265233623318251442244258454232422222544212344274"
+               88 )
+        ; test_case "real line 040" `Quick
+            (test_highest_joltage
+               "1212211622212622232222232221122222234222325251233221113223526233333222121362242225251522222122222412"
+               66 )
+        ; test_case "real line 041" `Quick
+            (test_highest_joltage
+               "1224243142354932247624132223442221243261122146133223131475431216123424343342231246215132422542144273"
+               97 )
+        ; test_case "real line 042" `Quick
+            (test_highest_joltage
+               "2492338342383524333242442252453454334643633243343233244463532534334332436821235243322432152236224423"
+               98 )
+        ; test_case "real line 043" `Quick
+            (test_highest_joltage
+               "7676556546555455945548897555565858677556364454655765687644455555553584455358535855555564435524555636"
+               99 )
+        ; test_case "real line 044" `Quick
+            (test_highest_joltage
+               "4325352353133335234532433545335543523225232353214622764538523233325246333312335343542333525343352832"
+               88 )
+        ; test_case "real line 045" `Quick
+            (test_highest_joltage
+               "3645465557845534765556456438425473478555654328555485735454543757533734857854555473533459558165456246"
+               98 )
+        ; test_case "real line 046" `Quick
+            (test_highest_joltage
+               "4112321222222221222222222212221112212222222213112212233222211122121222223233221122122112222222312222"
+               43 )
+        ; test_case "real line 047" `Quick
+            (test_highest_joltage
+               "3443534216134325237234252533391415524526262523352143237242332332332422332332347132554552354213163423"
+               97 )
+        ; test_case "real line 048" `Quick
+            (test_highest_joltage
+               "3233233443433352233334353335313474353433313433333332332445324732323333325354333345123333238333323343"
+               84 )
+        ; test_case "real line 049" `Quick
+            (test_highest_joltage
+               "2133222332312231142332122412332211233373432222221234222233216312322233333313213322233312422332412321"
+               76 )
+        ; test_case "real line 050" `Quick
+            (test_highest_joltage
+               "2323442214442251652225322254455617413464434422211515255422722166366711262534452258439143226431422432"
+               96 )
+        ; test_case "real line 051" `Quick
+            (test_highest_joltage
+               "3112243242223312224423222512422243342333412424122234223224524214241424224424422232231222421343123313"
+               55 )
+        ; test_case "real line 052" `Quick
+            (test_highest_joltage
+               "2524625652353456554546431455532426742414535225832464326233444242524314463569626432264234665412452611"
+               96 )
+        ; test_case "real line 053" `Quick
+            (test_highest_joltage
+               "2623224224152132332532122544116272213711472512222547253263227634222862855322152332253264721222222626"
+               88 )
+        ; test_case "real line 054" `Quick
+            (test_highest_joltage
+               "3413862324452342446454316341334346457442436472446424131344156965335463455345446483132552535546336316"
+               98 )
+        ; test_case "real line 055" `Quick
+            (test_highest_joltage
+               "5354344333214443434343442334124434322442443544435334333334544442334442344432244334534423233345433234"
+               55 )
+        ; test_case "real line 056" `Quick
+            (test_highest_joltage
+               "2322333211233223212213111213123244423222222232323332222322212221323323433322435233232371222222214231"
+               74 )
+        ; test_case "real line 057" `Quick
+            (test_highest_joltage
+               "9453214484824262259522856649224244244222211592233334238214222322284346591381262187242644522629832223"
+               99 )
+        ; test_case "real line 058" `Quick
+            (test_highest_joltage
+               "1121224242322123123163448337222562512232262643222323252252223543512425222422222223142233221426365461"
+               87 )
+        ; test_case "real line 059" `Quick
+            (test_highest_joltage
+               "1815612518244643515355768361121163421324442178622168752374328877665672243587235441472714316317588369"
+               89 )
+        ; test_case "real line 060" `Quick
+            (test_highest_joltage
+               "3655264263765432665494374452246362724532226675513545216322644525426252338564464426261732379225267837"
+               99 )
+        ; test_case "real line 061" `Quick
+            (test_highest_joltage
+               "8334743433235341445622143424833423324734232433333132424333763435142253533364333734887344542326984333"
+               98 )
+        ; test_case "real line 062" `Quick
+            (test_highest_joltage
+               "6333532332533333262332333332623323523436233333331335433333433323333133233344333378336333352223333232"
+               86 )
+        ; test_case "real line 063" `Quick
+            (test_highest_joltage
+               "3366253633632333372333133255934725232323263352222274223213323533141234362324236915143323333136434233"
+               99 )
+        ; test_case "real line 064" `Quick
+            (test_highest_joltage
+               "5322222323283352224135234432224523225232853242442423241544234623253324537257221444443224442542343223"
+               88 )
+        ; test_case "real line 065" `Quick
+            (test_highest_joltage
+               "2322722344168237322333228462433332227336523244323265343321333443434132333343333492223332435724342464"
+               97 )
+        ; test_case "real line 066" `Quick
+            (test_highest_joltage
+               "5554845434744255655687844665866661355767464556478385448756657654567285577634695565556616935646635793"
+               99 )
+        ; test_case "real line 067" `Quick
+            (test_highest_joltage
+               "6212623112233212232222321423231243253343231323432932323232222135322122237222134283242231231725212252"
+               98 )
+        ; test_case "real line 068" `Quick
+            (test_highest_joltage
+               "3224333333132232431414376222443332422422322223342332333335333224256832733233433622542324333442322953"
+               95 )
+        ; test_case "real line 069" `Quick
+            (test_highest_joltage
+               "1495248962734145243214425252551493515624456535246426262254542145634343245522513375341266233457656414"
+               99 )
+        ; test_case "real line 070" `Quick
+            (test_highest_joltage
+               "3333243514122577341633436443431333234233434851333432454335423136533335534834354554332443233443334233"
+               88 )
+        ; test_case "real line 071" `Quick
+            (test_highest_joltage
+               "6775435378454755775937393515454694792745716493599675572454465734647574159354586497336464643987566774"
+               99 )
+        ; test_case "real line 072" `Quick
+            (test_highest_joltage
+               "3343255423334231444544444344434343234333434343544344434524254354244544424452234444333442244454345533"
+               55 )
+        ; test_case "real line 073" `Quick
+            (test_highest_joltage
+               "5644753727566756775567545585754676596645654664776746756665476666666556676466474667695655766564656657"
+               99 )
+        ; test_case "real line 074" `Quick
+            (test_highest_joltage
+               "4644226464352276354314244224452454342423454622134648332554423425336244425432349642233521244367349342"
+               99 )
+        ; test_case "real line 075" `Quick
+            (test_highest_joltage
+               "3433335543445753633424571853934424332643345643544683232351242335433242324425464344622364532352533437"
+               98 )
+        ; test_case "real line 076" `Quick
+            (test_highest_joltage
+               "4332333343143333333343333474334265443333334214354551322433433243313234333232425433333443443433526343"
+               76 )
+        ; test_case "real line 077" `Quick
+            (test_highest_joltage
+               "4353646245233554434324342343533543343355335434535413535233331345445333253655446433354372556332324562"
+               76 )
+        ; test_case "real line 078" `Quick
+            (test_highest_joltage
+               "4325222211212322234523222222252532247122313123373542232242121352322276216822338182262236346922722222"
+               97 )
+        ; test_case "real line 079" `Quick
+            (test_highest_joltage
+               "2322565523552147152522424415733545252325565263526635227432457357155822584542343524555344525552453543"
+               88 )
+        ; test_case "real line 080" `Quick
+            (test_highest_joltage
+               "2536964744575897532331584947348473443439336365524543425393413335486443645364675453424543335446555498"
+               99 )
+        ; test_case "real line 081" `Quick
+            (test_highest_joltage
+               "2222213441222221121213232422422313244252223442212222212522422224224223231124422422243512212213212342"
+               55 )
+        ; test_case "real line 082" `Quick
+            (test_highest_joltage
+               "2226345127525427354274576964233625784361152623467725726752473254364464625478727754525322265247112673"
+               98 )
+        ; test_case "real line 083" `Quick
+            (test_highest_joltage
+               "3333323323439434233332343233242333523333333322324323333432333327112333312433423132233322331432333323"
+               97 )
+        ; test_case "real line 084" `Quick
+            (test_highest_joltage
+               "3333434534333424243331497446456437324756447475342274464232844334833254353445422233546141144533344344"
+               98 )
+        ; test_case "real line 085" `Quick
+            (test_highest_joltage
+               "3696167353668222145864766623627542566388745676275342437244534257633357663535464676463344222466874743"
+               98 )
+        ; test_case "real line 086" `Quick
+            (test_highest_joltage
+               "2221243212226232221214225213222212321222322222222222321222213152222212232613223422294232232522123112"
+               95 )
+        ; test_case "real line 087" `Quick
+            (test_highest_joltage
+               "2322223332222333222222322222224233422221212122124224222442422313242232322322322132221232323232224243"
+               44 )
+        ; test_case "real line 088" `Quick
+            (test_highest_joltage
+               "3222473241422323343212233253252455323361331212425233323243431532523435223231512332242372313333353233"
+               77 )
+        ; test_case "real line 089" `Quick
+            (test_highest_joltage
+               "5423224242232312223222322332344353122123124433226352334261254221453422322421343522321125621432243323"
+               66 )
+        ; test_case "real line 090" `Quick
+            (test_highest_joltage
+               "8363335374334533365422233335351363332233354423323122333333234434223223333335635423442344353624352436"
+               87 )
+        ; test_case "real line 091" `Quick
+            (test_highest_joltage
+               "3363445765667922559186654477737547964555446686459554733657654766566655765548166378754867769354765564"
+               99 )
+        ; test_case "real line 092" `Quick
+            (test_highest_joltage
+               "6533212432223424334451322232232232443253324232723281475224244243554253222475635635422425222222222428"
+               88 )
+        ; test_case "real line 093" `Quick
+            (test_highest_joltage
+               "1223233332437322323134322352329283423333133433331533223722733221342425515333543413253332323254332144"
+               98 )
+        ; test_case "real line 094" `Quick
+            (test_highest_joltage
+               "5264162233623746665261784343112243254221441535263624414528422142852361426326676128424382222772232624"
+               88 )
+        ; test_case "real line 095" `Quick
+            (test_highest_joltage
+               "1222232222322322212232232122232322222331222223323232222322212223221222223122132222222226222311212222"
+               63 )
+        ; test_case "real line 096" `Quick
+            (test_highest_joltage
+               "2447938353242561333434522543524366633338233372322372443172638272362414623239322222214322338432223233"
+               99 )
+        ; test_case "real line 097" `Quick
+            (test_highest_joltage
+               "4884849914558496499986874887474387879218486546454756422444585589669397378725447645287563673434787636"
+               99 )
+        ; test_case "real line 098" `Quick
+            (test_highest_joltage
+               "1532312355432455353342333225253523373245346353222322243344325423634342343333235353462335235134532214"
+               76 )
+        ; test_case "real line 099" `Quick
+            (test_highest_joltage
+               "3633115526253432364354661645232316365446622332424352521423265511535341213222665264163264143532241789"
+               89 )
+        ; test_case "real line 100" `Quick
+            (test_highest_joltage
+               "1333723464325672225363386433359834138466234942326568553333727332463624757374234473543533336465426327"
+               99 )
+        ; test_case "real line 101" `Quick
+            (test_highest_joltage
+               "8325733945242354443883554334669457355644376375344222347347435474443336786843454755374733473222713744"
+               99 )
+        ; test_case "real line 102" `Quick
+            (test_highest_joltage
+               "3836536232345525523424516573323367655557875645136254455455455555237343456565656555565433564652375615"
+               88 )
+        ; test_case "real line 103" `Quick
+            (test_highest_joltage
+               "1222242222222222222221222222222222222222222222214222242212122221223267222222112122222222222221223723"
+               77 )
+        ; test_case "real line 104" `Quick
+            (test_highest_joltage
+               "2122322223222221341225222331152222221222222221222222222212223231322221121224122222222221222322221221"
+               55 )
+        ; test_case "real line 105" `Quick
+            (test_highest_joltage
+               "2623431563346525416242365622564363427642123425242364433596524126242622114536213245235652674623263514"
+               97 )
+        ; test_case "real line 106" `Quick
+            (test_highest_joltage
+               "2232456232323314322243433252432326454256232632225662224221422412232162235555244527334626356269224262"
+               96 )
+        ; test_case "real line 107" `Quick
+            (test_highest_joltage
+               "2223224223121316212222123214122222321222232222214222223322235255232321232421222233223123422332226121"
+               66 )
+        ; test_case "real line 108" `Quick
+            (test_highest_joltage
+               "2232222211641215121113421342225332233222241313112621422223224321232326222212352222222222322222232142"
+               66 )
+        ; test_case "real line 109" `Quick
+            (test_highest_joltage
+               "3622224322123323543363333123532223522232121233221223212255624222224222331222232221222223332412252226"
+               66 )
+        ; test_case "real line 110" `Quick
+            (test_highest_joltage
+               "2133111331232311212423441441423422333433421444124423221341431323413244441112422424242124214412256789"
+               89 )
+        ; test_case "real line 111" `Quick
+            (test_highest_joltage
+               "4324434435333333333334332245243563333343356334334344235334322234145353323234352455374364553333643433"
+               76 )
+        ; test_case "real line 112" `Quick
+            (test_highest_joltage
+               "3644734534756433422432434356624552253427466225337526564429422436344444454366324544253633541443353244"
+               96 )
+        ; test_case "real line 113" `Quick
+            (test_highest_joltage
+               "2464324635364431443472344454334444343433464546454374434442423242443446444423526443551333243353834444"
+               84 )
+        ; test_case "real line 114" `Quick
+            (test_highest_joltage
+               "5281642433245222222262522922521227221222224253247163523362225212277164151212258322522132327215231222"
+               98 )
+        ; test_case "real line 115" `Quick
+            (test_highest_joltage
+               "4235325226444533343235413742346432342321545545344233233255443834433325423232343235231352342354622553"
+               86 )
+        ; test_case "real line 116" `Quick
+            (test_highest_joltage
+               "8733361224233225222222426322442381855225483432261538256252524243235345825178218568965722348222331146"
+               98 )
+        ; test_case "real line 117" `Quick
+            (test_highest_joltage
+               "3464344445243346232343434322224234534583235444432447445343449318343349436245884322482543363363441674"
+               99 )
+        ; test_case "real line 118" `Quick
+            (test_highest_joltage
+               "7343334231474233525283342422364511453342252222452242451442434432112333432342315946241522245542222535"
+               96 )
+        ; test_case "real line 119" `Quick
+            (test_highest_joltage
+               "4446143264553864474334554447535535453446566233244444636634565645448343225453554444454544364443454574"
+               88 )
+        ; test_case "real line 120" `Quick
+            (test_highest_joltage
+               "2422842224224342322263252223333244522315113324152212372221342231322244231232122332222112227625141222"
+               87 )
+        ; test_case "real line 121" `Quick
+            (test_highest_joltage
+               "4142122222422221222412122222212544522231222223211322362222321222222134432222122542122262223523223222"
+               66 )
+        ; test_case "real line 122" `Quick
+            (test_highest_joltage
+               "4572333542142432343332342132323444433243433454242321332323354233213344233432132323534221333344323134"
+               75 )
+        ; test_case "real line 123" `Quick
+            (test_highest_joltage
+               "1333235433322333324332333323332332233112331232333422333333333235333334322322333323333333323333423735"
+               75 )
+        ; test_case "real line 124" `Quick
+            (test_highest_joltage
+               "5563657356454636674393696655654548835664676555834625756663576376694963475267652644487768866556366963"
+               99 )
+        ; test_case "real line 125" `Quick
+            (test_highest_joltage
+               "4563325436233211733422223372423424234244425452243133154466242445642433343224441473324372257264523657"
+               77 )
+        ; test_case "real line 126" `Quick
+            (test_highest_joltage
+               "2323232163222222141214222333122231122223522528112323222223222322213223223322333322221323333333322311"
+               83 )
+        ; test_case "real line 127" `Quick
+            (test_highest_joltage
+               "2122222234242122427222222226222332211222112222222211222421121538222231222313221435322311232222212242"
+               85 )
+        ; test_case "real line 128" `Quick
+            (test_highest_joltage
+               "5334253235515121222383422225322212542617232476242645322652351543223434635325223237112254433523422324"
+               87 )
+        ; test_case "real line 129" `Quick
+            (test_highest_joltage
+               "1221223532146222222223126712218222123621122123217221212222322221232621162221122222222222122561122292"
+               92 )
+        ; test_case "real line 130" `Quick
+            (test_highest_joltage
+               "1253352424255222142243514444444457255254363328422562213135526512123451523416645352425253125322532244"
+               86 )
+        ; test_case "real line 131" `Quick
+            (test_highest_joltage
+               "7463373334646423355538441534433248593244576575237356213443653633273543376463332733333713232643554552"
+               97 )
+        ; test_case "real line 132" `Quick
+            (test_highest_joltage
+               "5752323474332773249344434354245224321731245442414442735261654665534764636524293424214244444723343251"
+               99 )
+        ; test_case "real line 133" `Quick
+            (test_highest_joltage
+               "2629438637852334643554943482775533446535956343762325623453474525365936398476244597355454656623443534"
+               99 )
+        ; test_case "real line 134" `Quick
+            (test_highest_joltage
+               "4535534443563253332234233434455543533235333233223442233533235354443333733435443343553354434434423313"
+               75 )
+        ; test_case "real line 135" `Quick
+            (test_highest_joltage
+               "3432223113423243423323513443123332315562232532523473232212343355364222323234236322343323225332327733"
+               77 )
+        ; test_case "real line 136" `Quick
+            (test_highest_joltage
+               "1425245335243124322324153454554115125214321244121112544441331342553344311545421455324424455134156789"
+               89 )
+        ; test_case "real line 137" `Quick
+            (test_highest_joltage
+               "5132222223252224223252622414436422231243232252214255323634524534432233273222325435334426442424422223"
+               76 )
+        ; test_case "real line 138" `Quick
+            (test_highest_joltage
+               "3466444436255433325573352262554776625733275447321246237454234455234514752545552532447415643534223435"
+               77 )
+        ; test_case "real line 139" `Quick
+            (test_highest_joltage
+               "3421133222332332322343231232212233662233221312321122224431322313262333313232332243223222233232344323"
+               66 )
+        ; test_case "real line 140" `Quick
+            (test_highest_joltage
+               "3333523333232364333363555455431345243544566532455235335641243353444455452225735366346344243452243545"
+               76 )
+        ; test_case "real line 141" `Quick
+            (test_highest_joltage
+               "2152354211122622723432615322212523224222225212363121124451232267516325421252122342152252424221452215"
+               77 )
+        ; test_case "real line 142" `Quick
+            (test_highest_joltage
+               "1336123121333343222232333212232411534322333233223332323322234351332222331333333233332312233311232332"
+               65 )
+        ; test_case "real line 143" `Quick
+            (test_highest_joltage
+               "2132121232233134232221223353223332232233322251223526132523323234323223335333222534212113232222523324"
+               65 )
+        ; test_case "real line 144" `Quick
+            (test_highest_joltage
+               "5642633765534226222523623324323443222227261332774392232227443393254412356235358631224418312923222245"
+               99 )
+        ; test_case "real line 145" `Quick
+            (test_highest_joltage
+               "8253442425732222332238822732425826242143236154326323242443342334348324234372622433223442523324133216"
+               88 )
+        ; test_case "real line 146" `Quick
+            (test_highest_joltage
+               "2232271226257223212222421324222344224222141222322222222222222122224238422414316422323222222322127221"
+               87 )
+        ; test_case "real line 147" `Quick
+            (test_highest_joltage
+               "6446315487414253623366432633565653444341454233666544632655534656536436114486263961512465435546514714"
+               97 )
+        ; test_case "real line 148" `Quick
+            (test_highest_joltage
+               "3452383332535514435334232222355452522134243132532453384334525234222233545425333315332323214145535341"
+               88 )
+        ; test_case "real line 149" `Quick
+            (test_highest_joltage
+               "3232222223322222122123232312331213231232227213222242313323222122223322222322313334222122231232221331"
+               74 )
+        ; test_case "real line 150" `Quick
+            (test_highest_joltage
+               "3424332322222132232233231123121313223223263323323222342313211312222322221122422223222112232122222222"
+               64 )
+        ; test_case "real line 151" `Quick
+            (test_highest_joltage
+               "4688454513726334654565476674454433554682654943685644463375763364523442437445697396743545599524274524"
+               99 )
+        ; test_case "real line 152" `Quick
+            (test_highest_joltage
+               "4161223222271222942312171248122235227112222552223422326624121622234732522212222232212366825223253121"
+               98 )
+        ; test_case "real line 153" `Quick
+            (test_highest_joltage
+               "6332465533333522555433324356221543352235533566333253334365565323363324552432332233335334227623136325"
+               76 )
+        ; test_case "real line 154" `Quick
+            (test_highest_joltage
+               "3222431333842318323144411327346223122314332323123555122522333732335233333352312534852241433483632313"
+               88 )
+        ; test_case "real line 155" `Quick
+            (test_highest_joltage
+               "2112121212253222222943424322422222512112212312422234143313232222122122222122123122132137327212242242"
+               97 )
+        ; test_case "real line 156" `Quick
+            (test_highest_joltage
+               "3222532316332422221212223221522223111252221221322212217222213222221221211241222312222121222133222221"
+               74 )
+        ; test_case "real line 157" `Quick
+            (test_highest_joltage
+               "2323332223344321223143245373113722211223122226227822325314633213361321445632321823462822337223222445"
+               88 )
+        ; test_case "real line 158" `Quick
+            (test_highest_joltage
+               "1828425212144411422233221323218468423217466223581342222211242262211332238228121222224225122212222232"
+               88 )
+        ; test_case "real line 159" `Quick
+            (test_highest_joltage
+               "3556334454665634545845243453255635572675157347763125427524341342644935377436635334453443684644784434"
+               98 )
+        ; test_case "real line 160" `Quick
+            (test_highest_joltage
+               "2645662623422533225421215431512343431254242214262232525122522244211222145253265353435325571322222253"
+               75 )
+        ; test_case "real line 161" `Quick
+            (test_highest_joltage
+               "2224222242122222222232211112222314222222222234412242326322512423222222232623322222122322112321211122"
+               66 )
+        ; test_case "real line 162" `Quick
+            (test_highest_joltage
+               "3323122223222222333232562133233231243322232322321321232232332322335422322313322223123222222334233322"
+               65 )
+        ; test_case "real line 163" `Quick
+            (test_highest_joltage
+               "3221132223233221322222223221222241223222221222212214223422121422222452222224223222122124212323123221"
+               54 )
+        ; test_case "real line 164" `Quick
+            (test_highest_joltage
+               "2221442252281322222422127282212412222622221232731222223242124222212112212222241262321442522221122252"
+               88 )
+        ; test_case "real line 165" `Quick
+            (test_highest_joltage
+               "2133231122331441531433375353572447432322146333423223632556232232334447444433622228242422332343332434"
+               84 )
+        ; test_case "real line 166" `Quick
+            (test_highest_joltage
+               "5563624513351533334437333324353335333533533355223433335233342353363556423235334233344323342524634321"
+               76 )
+        ; test_case "real line 167" `Quick
+            (test_highest_joltage
+               "2332432233323221431231323223332233383122222132424421134132233232323333433435254432332222332323313232"
+               85 )
+        ; test_case "real line 168" `Quick
+            (test_highest_joltage
+               "2423222822122222222412282231122429224143222242222222223223436242424223242432142221433121142143522227"
+               97 )
+        ; test_case "real line 169" `Quick
+            (test_highest_joltage
+               "1368838843358743334345324211363655364233733332443334321243322336412538532344213423253222366323263695"
+               95 )
+        ; test_case "real line 170" `Quick
+            (test_highest_joltage
+               "4744137463363333333332326343314643324446233366376545372648324744635334435237267661327145553246452321"
+               87 )
+        ; test_case "real line 171" `Quick
+            (test_highest_joltage
+               "3831332122233231223233222433232333233133133242242331362323323332235244434223336362233433352322334423"
+               86 )
+        ; test_case "real line 172" `Quick
+            (test_highest_joltage
+               "3214422223143421344222143132231445423222522643233323314323424344434731323334224323324533352334332442"
+               75 )
+        ; test_case "real line 173" `Quick
+            (test_highest_joltage
+               "3543312373344332233323452214433346347334844253532442224222234312433329254329453434283232534223272192"
+               99 )
+        ; test_case "real line 174" `Quick
+            (test_highest_joltage
+               "3433383314338373834351844233646343475553142224453454325446354334653275541333543135354465333263445242"
+               88 )
+        ; test_case "real line 175" `Quick
+            (test_highest_joltage
+               "4432372233684255322525272434647435924424322624541334413224443634326336461361436414475721222543446321"
+               97 )
+        ; test_case "real line 176" `Quick
+            (test_highest_joltage
+               "5433335293334525543224371764333434988333237353113448943411932743514583594643353323325387583814645347"
+               99 )
+        ; test_case "real line 177" `Quick
+            (test_highest_joltage
+               "5444424957443468654656364755567468455486545344445776761776566466566644555557658947447467449455766646"
+               99 )
+        ; test_case "real line 178" `Quick
+            (test_highest_joltage
+               "2523333233343235435222235534333238434254233255342853335554453253236223223533323533522334332433432543"
+               88 )
+        ; test_case "real line 179" `Quick
+            (test_highest_joltage
+               "1138614552342221321221222413621222223231223222323222814623241222446214226442469244351324343452225242"
+               95 )
+        ; test_case "real line 180" `Quick
+            (test_highest_joltage
+               "3235222332131222222123223222332312322323172132141232121324222213353223224233213123222221223322233343"
+               75 )
+        ; test_case "real line 181" `Quick
+            (test_highest_joltage
+               "4255452362323165242342332223332343343253334456143314452223324924424332355355353341343334425553353324"
+               95 )
+        ; test_case "real line 182" `Quick
+            (test_highest_joltage
+               "3544633234326333143434434638432333354444353822424442333225332444532646543132326565233146643454534545"
+               88 )
+        ; test_case "real line 183" `Quick
+            (test_highest_joltage
+               "5533866835333332446339845544234435374366623344443448343635433373544333343634473633534344325836364423"
+               98 )
+        ; test_case "real line 184" `Quick
+            (test_highest_joltage
+               "2125222512312522233222222532263455412421222232122112222113222512244225244211543622122111124332312445"
+               66 )
+        ; test_case "real line 185" `Quick
+            (test_highest_joltage
+               "5765537453753546524944644454354364643373535664333265356565454434334362334636443764473516535345363344"
+               97 )
+        ; test_case "real line 186" `Quick
+            (test_highest_joltage
+               "1242333313323541312121335173323322252262322222223242223232232232334313232372223332333223325322223324"
+               77 )
+        ; test_case "real line 187" `Quick
+            (test_highest_joltage
+               "4945346555344725534444354865365546455455453445376994344537749854443434373543557699323594547559554353"
+               99 )
+        ; test_case "real line 188" `Quick
+            (test_highest_joltage
+               "8441321232536757468212413223835223356252342241323333442736423243742453922327334232628243572272153736"
+               98 )
+        ; test_case "real line 189" `Quick
+            (test_highest_joltage
+               "3233227533534655473331231323541242222614244236242111121212233442265222232434532624232622312564515622"
+               77 )
+        ; test_case "real line 190" `Quick
+            (test_highest_joltage
+               "5231443534475571334243142383154324332422432224554332949237335344432225546623266434742645424452245374"
+               99 )
+        ; test_case "real line 191" `Quick
+            (test_highest_joltage
+               "2222652752542951212254142576134913223231244514325577152312242364152242322223322323734226324612251433"
+               99 )
+        ; test_case "real line 192" `Quick
+            (test_highest_joltage
+               "3344232272222124265242432232223224453423221222354325223634222122333255463333115233242332132134223228"
+               78 )
+        ; test_case "real line 193" `Quick
+            (test_highest_joltage
+               "2423211646221222214223621414422342222242214622426224222474221222222215322142322234542433223122532751"
+               77 )
+        ; test_case "real line 194" `Quick
+            (test_highest_joltage
+               "1222432222227322222223122113222321223327322223241223322232332322222222222222123323434222222223412222"
+               77 )
+        ; test_case "real line 195" `Quick
+            (test_highest_joltage
+               "2231222262245222221524294251251222212942222142532633726213522122212422222232121922212212262322231242"
+               99 )
+        ; test_case "real line 196" `Quick
+            (test_highest_joltage
+               "3436674387463373644336847545353373813336332865333426743634647353343363237627393333883956336933349336"
+               99 )
+        ; test_case "real line 197" `Quick
+            (test_highest_joltage
+               "4234664334533643445662346466345666647426655444553533366634453846446264346586345365444765364634443146"
+               88 )
+        ; test_case "real line 198" `Quick
+            (test_highest_joltage
+               "4141324433423632324233334423343324244241332653544345362343464242132445242521322431444734316223541332"
+               76 )
+        ; test_case "real line 199" `Quick
+            (test_highest_joltage
+               "3535726262552245152262222275133232659846242165522221422176222262567254622235412424626225322313236476"
+               98 )
+        ; test_case "real line 200" `Quick
+            (test_highest_joltage
+               "2222222333136722224325232232111133222432346324431421212343222142244331223225124653223222322121232213"
+               76 ) ] )
+    ; ( "BatteryBank.highest_joltage regression"
+      , [ test_case
+            "second digit promoted when same digit found and greater than \
+             first digit"
+            `Quick
+            (test_highest_joltage "343400" 44)
+        ; test_case "second last digit skipped" `Quick
+            (test_highest_joltage "789" 89)
+        ; test_case "I have no idea why this is wrong yet" `Quick
+            (test_highest_joltage "565" 65)
+        ; test_case "I have no idea why this is right yet" `Quick
+            (test_highest_joltage "566" 66)
+        ; test_case "I have no idea why this is right yet" `Quick
+            (test_highest_joltage "06760" 76)
+        ; test_case "I have no idea why this is wrong yet" `Quick
+            (test_highest_joltage "0067600" 76) ] )
+    ; ( "BatteryBank property tests"
+      , List.map
+          (QCheck_alcotest.to_alcotest ~colors:true)
+          [largest_digit_always_in_highest_joltage] ) ]
diff --git a/ocaml/test/infrastructure/dune b/ocaml/test/infrastructure/dune
new file mode 100644
index 0000000..5d493d9
--- /dev/null
+++ b/ocaml/test/infrastructure/dune
@@ -0,0 +1,8 @@
+(tests
+ (names
+   test_example)
+ (libraries
+   application
+   domain
+   infrastructure
+   alcotest))
diff --git a/ocaml/test/infrastructure/test_example.ml b/ocaml/test/infrastructure/test_example.ml
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/ocaml/test/infrastructure/test_example.ml
diff --git a/ocaml/test/presentation/dune b/ocaml/test/presentation/dune
new file mode 100644
index 0000000..e34e56f
--- /dev/null
+++ b/ocaml/test/presentation/dune
@@ -0,0 +1,11 @@
+(tests
+ (names
+   test_example)
+ (libraries
+   application
+   domain
+   infrastructure
+   presentation
+   alcotest
+   qcheck-core
+   qcheck-alcotest))
diff --git a/ocaml/test/presentation/test_example.ml b/ocaml/test/presentation/test_example.ml
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/ocaml/test/presentation/test_example.ml