Enable Hamming test generator (#551)

This can now be enabled now that the "reimplements" key is honoured.

Author: TheRealOwenRees

exercises/practice/hamming/.meta/example.ml

@@ -2,22 +2,11 @@ open Base
 
 type nucleotide = A | C | G | T
 
-let equal (x,y) = match (x, y) with
-| (A, A) -> true
-| (C, C) -> true
-| (G, G) -> true
-| (T, T) -> true
-| _ -> false
-
-let to_result (l: 'a List.Or_unequal_lengths.t): ('a, string) Result.t = 
-  let open List.Or_unequal_lengths in
-  match l with 
-  | Unequal_lengths -> Error "left and right strands must be of equal length" 
-  | Ok x -> Ok x
+let equal (x, y) = match (x, y) with
+  | (A, A) | (C, C) | (G, G) | (T, T) -> true
+  | _ -> false
 
 let hamming_distance a b =
-  match (List.is_empty a, List.is_empty b) with
-  | (true, false) -> Error "left strand must not be empty" 
-  | (false, true) -> Error "right strand must not be empty"
-  | _ -> List.zip a b |> to_result |> Result.map ~f:(List.count ~f:(Fn.non equal))
-
+  match List.zip a b with
+  | Unequal_lengths -> Error "strands must be of equal length"
+  | Ok pairs -> Ok (List.count pairs ~f:(Fn.non equal))

exercises/practice/hamming/dune-project

@@ -1,2 +1,2 @@
 (lang dune 1.1)
-(version 2.3.0)
+(version 1.0)

exercises/practice/hamming/test.ml

@@ -1,4 +1,4 @@
-(* hamming - 2.3.0 *)
+(* hamming - 1.0 *)
 open Base
 open OUnit2
 open Hamming
@@ -32,13 +32,13 @@ let tests = [
   "long different strands" >::
   ae (Ok 9) (hamdist "GGACGGATTCTG" "AGGACGGATTCT");
   "disallow first strand longer" >::
-  ae  (Error "left and right strands must be of equal length") (hamdist "AATG" "AAA");
+  ae  (Error "strands must be of equal length") (hamdist "AATG" "AAA");
   "disallow second strand longer" >::
-  ae  (Error "left and right strands must be of equal length") (hamdist "ATA" "AGTG");
-  "disallow left empty strand" >::
-  ae  (Error "left strand must not be empty") (hamdist "" "G");
-  "disallow right empty strand" >::
-  ae  (Error "right strand must not be empty") (hamdist "G" "");
+  ae  (Error "strands must be of equal length") (hamdist "ATA" "AGTG");
+  "disallow empty first strand" >::
+  ae  (Error "strands must be of equal length") (hamdist "" "G");
+  "disallow empty second strand" >::
+  ae  (Error "strands must be of equal length") (hamdist "G" "");
 ]
 
 let () =