feat(range): implement range module for parsing ranges in the format "%d-%d"

1 files changed, 67 insertions, 0 deletions

diff --git a/2025/ocaml/lib/domain/range.ml b/2025/ocaml/lib/domain/range.ml
new file mode 100644
index 0000000..a1bdc00
--- /dev/null
+++ b/2025/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"]