refactor(2025,ocaml): use result type for answers to allow for returning errors

18 files changed, 156 insertions, 103 deletions

diff --git a/2025/ocaml/lib/application/d01p01.ml b/2025/ocaml/lib/application/d01p01.ml
index 75e1b17..206e757 100644
--- a/2025/ocaml/lib/application/d01p01.ml
+++ b/2025/ocaml/lib/application/d01p01.ml
@@ -1,5 +1,7 @@
 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 <> "")
@@ -42,8 +44,10 @@ let rec turn_aux count current = function
 let turn current = turn_aux 0 current
 
 let solve input () =
-  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
-  answer
+  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/2025/ocaml/lib/application/d01p01.mli b/2025/ocaml/lib/application/d01p01.mli
index 30ece9d..2eecf19 100644
--- a/2025/ocaml/lib/application/d01p01.mli
+++ b/2025/ocaml/lib/application/d01p01.mli
@@ -1,4 +1,4 @@
-val solve : string -> unit -> int
+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 0.
+    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/2025/ocaml/lib/application/d01p02.ml b/2025/ocaml/lib/application/d01p02.ml
index 6f935a4..7910486 100644
--- a/2025/ocaml/lib/application/d01p02.ml
+++ b/2025/ocaml/lib/application/d01p02.ml
@@ -1,5 +1,7 @@
 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 <> "")
@@ -44,8 +46,10 @@ let rec turn_aux count dial = function
 let turn current = turn_aux 0 current
 
 let solve input () =
-  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
-  answer
+  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/2025/ocaml/lib/application/d01p02.mli b/2025/ocaml/lib/application/d01p02.mli
index 33aa63f..9e9a2f2 100644
--- a/2025/ocaml/lib/application/d01p02.mli
+++ b/2025/ocaml/lib/application/d01p02.mli
@@ -1,4 +1,4 @@
-val solve : string -> unit -> int
+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 0.
+    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/2025/ocaml/lib/application/d02p01.ml b/2025/ocaml/lib/application/d02p01.ml
index ce8778d..f313149 100644
--- a/2025/ocaml/lib/application/d02p01.ml
+++ b/2025/ocaml/lib/application/d02p01.ml
@@ -1,5 +1,7 @@
 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". *)
@@ -37,11 +39,16 @@ let is_invalid = ID.validate rules
 let passthrough_with_logs logger lst = logger lst ; lst
 
 let solve input () =
-  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
+  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/2025/ocaml/lib/application/d02p01.mli b/2025/ocaml/lib/application/d02p01.mli
index 27f85d4..8a8eb32 100644
--- a/2025/ocaml/lib/application/d02p01.mli
+++ b/2025/ocaml/lib/application/d02p01.mli
@@ -1,4 +1,4 @@
-val solve : string -> unit -> int
+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 0.
+    The solution for an empty input is [Error msg].
     Requires: [input] to be a string. *)
diff --git a/2025/ocaml/lib/application/d02p02.ml b/2025/ocaml/lib/application/d02p02.ml
index 29e3877..d062f7b 100644
--- a/2025/ocaml/lib/application/d02p02.ml
+++ b/2025/ocaml/lib/application/d02p02.ml
@@ -1,5 +1,9 @@
 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]. *)
@@ -67,11 +71,16 @@ let is_invalid id =
   List.length repeating_patterns > 0
 
 let solve input () =
-  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
+  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/2025/ocaml/lib/application/d02p02.mli b/2025/ocaml/lib/application/d02p02.mli
index 27f85d4..8a8eb32 100644
--- a/2025/ocaml/lib/application/d02p02.mli
+++ b/2025/ocaml/lib/application/d02p02.mli
@@ -1,4 +1,4 @@
-val solve : string -> unit -> int
+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 0.
+    The solution for an empty input is [Error msg].
     Requires: [input] to be a string. *)
diff --git a/2025/ocaml/lib/application/d03p01.ml b/2025/ocaml/lib/application/d03p01.ml
index 691fe65..14f49e8 100644
--- a/2025/ocaml/lib/application/d03p01.ml
+++ b/2025/ocaml/lib/application/d03p01.ml
@@ -28,20 +28,27 @@
 
 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 () =
-  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
+  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
 
 let print_occurring_digits input () =
   input |> to_lines |> List.to_seq
@@ -52,14 +59,17 @@ let print_occurring_digits input () =
   |> Seq.iteri (fun idx bb ->
       Logs.debug (fun m -> m "%d %s" (idx + 1) (BatteryBank.pp bb)) ) ;
   -1
+(* disables unused function warning *)
+[@@warning "-32"]
 
-[@@warning "-32"] (* disables unused function warning *)
 let _solve' input () =
-  let banks =
-    input |> to_lines |> List.to_seq
-    |> Seq.map BatteryBank.of_string
-    |> Seq.map BatteryBank.to_list
-    |> Seq.map (fun bb -> List.map Battery.to_int bb)
-    |> List.of_seq
-  in
-  banks
+  if input = "" then Error err_empty_input
+  else
+    let banks =
+      input |> to_lines |> List.to_seq
+      |> Seq.map BatteryBank.of_string
+      |> Seq.map BatteryBank.to_list
+      |> Seq.map (fun bb -> List.map Battery.to_int bb)
+      |> List.of_seq
+    in
+    Ok banks
diff --git a/2025/ocaml/lib/application/d03p01.mli b/2025/ocaml/lib/application/d03p01.mli
index d875e40..b492753 100644
--- a/2025/ocaml/lib/application/d03p01.mli
+++ b/2025/ocaml/lib/application/d03p01.mli
@@ -1,6 +1,6 @@
-val solve : string -> unit -> int
+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 0.
+    The solution for an empty input is [Error msg].
     Requires: [input] to be a string. *)
 
 val print_occurring_digits : string -> unit -> int
diff --git a/2025/ocaml/lib/application/d04p01.ml b/2025/ocaml/lib/application/d04p01.ml
index 260c9e9..7c69de4 100644
--- a/2025/ocaml/lib/application/d04p01.ml
+++ b/2025/ocaml/lib/application/d04p01.ml
@@ -1,26 +1,32 @@
 open Domain
 
+let err_empty_input = "input is empty"
+
 let rec solve input () =
-  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 ;
-  !accessible_rolls_of_paper
+  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 =
diff --git a/2025/ocaml/lib/application/d04p01.mli b/2025/ocaml/lib/application/d04p01.mli
index 2fd4e44..873acff 100644
--- a/2025/ocaml/lib/application/d04p01.mli
+++ b/2025/ocaml/lib/application/d04p01.mli
@@ -1,4 +1,4 @@
-val solve : string -> unit -> int
+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 0.
+    The solution for an empty input is [Error msg].
     Requires: [input] to be a string. *)
diff --git a/2025/ocaml/lib/application/d04p02.ml b/2025/ocaml/lib/application/d04p02.ml
index 260c9e9..7c69de4 100644
--- a/2025/ocaml/lib/application/d04p02.ml
+++ b/2025/ocaml/lib/application/d04p02.ml
@@ -1,26 +1,32 @@
 open Domain
 
+let err_empty_input = "input is empty"
+
 let rec solve input () =
-  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 ;
-  !accessible_rolls_of_paper
+  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 =
diff --git a/2025/ocaml/lib/application/d04p02.mli b/2025/ocaml/lib/application/d04p02.mli
index 69c5181..388ec56 100644
--- a/2025/ocaml/lib/application/d04p02.mli
+++ b/2025/ocaml/lib/application/d04p02.mli
@@ -1,4 +1,4 @@
-val solve : string -> unit -> int
+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 0.
+    The solution for an empty input is [Error msg].
     Requires: [input] to be a string. *)
diff --git a/2025/ocaml/lib/presentation/cli.ml b/2025/ocaml/lib/presentation/cli.ml
index 371f199..b4c990c 100644
--- a/2025/ocaml/lib/presentation/cli.ml
+++ b/2025/ocaml/lib/presentation/cli.ml
@@ -2,8 +2,11 @@
 
 let run_solver name solver filepath =
   let content = Infrastructure.File.read filepath in
-  let answer = solver content () in
-  Logs.app (fun m -> m "[%s] ANSWER=%d" name answer)
+  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 ->
diff --git a/2025/ocaml/test/application/test_d01p01.ml b/2025/ocaml/test/application/test_d01p01.ml
index 70f5ab2..e57db01 100644
--- a/2025/ocaml/test/application/test_d01p01.ml
+++ b/2025/ocaml/test/application/test_d01p01.ml
@@ -12,7 +12,9 @@ R14
 L82|}
 
 let test_full_given_example () =
-  Alcotest.(check int) "full given example" 3 (solve example_data ())
+  Alcotest.(check int)
+    "full given example" 3
+    (match solve example_data () with Error _ -> 0 | Ok ans -> ans)
 
 let () =
   let open Alcotest in
diff --git a/2025/ocaml/test/application/test_d01p02.ml b/2025/ocaml/test/application/test_d01p02.ml
index e29c932..bbda035 100644
--- a/2025/ocaml/test/application/test_d01p02.ml
+++ b/2025/ocaml/test/application/test_d01p02.ml
@@ -12,7 +12,9 @@ R14
 L82|}
 
 let test_full_given_example () =
-  Alcotest.(check int) "full given example" 6 (solve example_data ())
+  Alcotest.(check int)
+    "full given example" 6
+    (match solve example_data () with Error _ -> 0 | Ok ans -> ans)
 
 let () =
   let open Alcotest in
diff --git a/2025/ocaml/test/application/test_d04p01.ml b/2025/ocaml/test/application/test_d04p01.ml
index 783659e..ffbe102 100644
--- a/2025/ocaml/test/application/test_d04p01.ml
+++ b/2025/ocaml/test/application/test_d04p01.ml
@@ -14,7 +14,7 @@ let example =
 
 let test_input_to_matrix have want () =
   Alcotest.(check int) "number of rolls of paper that are accessible" want
-  @@ solve have ()
+  @@ match solve have () with Error _ -> 0 | Ok ans -> ans
 
 let () =
   let open Alcotest in