Make OCaml code samples closer to Haskell (chapters 1 to 4)

- Get rid of module declarations
- Use only OCaml Stdlib
- Rename composition operator to `(%)` due to operator precedence issues

src/content/1.1/code/ocaml/snippet01.ml

@@ -1,6 +1 @@
-module type Polymorphic_Function_F = sig
-  type a
-  type b
-
-  val f : a -> b
-end
+val f : a -> b

src/content/1.1/code/ocaml/snippet02.ml

@@ -1,6 +1 @@
-module type Polymorphic_Function_G = sig
-  type b
-  type c
-
-  val g : b -> c
-end
+val g : b -> c

src/content/1.1/code/ocaml/snippet03.ml

@@ -1,9 +1,3 @@
-module Compose_Example
-    (F : Polymorphic_Function_F)
-    (G : Polymorphic_Function_G with type b = F.b) =
-struct
-  (** OCaml doesn't have a compose operator. So, creating one. **)
-  let ( >> ) g f x = g (f x)
-
-  let compose : 'a -> 'c = G.g >> F.f
-end
+(** OCaml doesn't have a compose operator. So, creating one. **)
+let ( % ) g f x = g (f x)
+g % f

src/content/1.1/code/ocaml/snippet04.ml

@@ -1,9 +1,5 @@
-module Compose_Three_GF = functor(F:Polymorphic_Function_F)(G:Polymorphic_Function_G with type b = F.b)(H:Polymorphic_Function_H with type c = G.c) -> struct
-  let compose : 'a -> 'd = H.h >> (G.g >> F.f)
-end
+val f : a -> b
+val g : b -> c
+val h : c -> d
 
-module Compose_Three_HG = functor(F:Polymorphic_Function_F)(G:Polymorphic_Function_G with type b = F.b)(H:Polymorphic_Function_H with type c = G.c) -> struct
-  let compose : 'a -> 'd = (H.h >> G.g) >> F.f
-end
-
-Compose_Three_GF.compose = Compose_Three_HG.compose
+h % (g % f) = (h % g) % f = h % g % f

src/content/1.1/code/ocaml/snippet06.ml

@@ -1,2 +1,2 @@
-f >> id
-id >> f
+f % id = f
+id % f = f

src/content/1.2/code/ocaml/snippet01.ml

@@ -1,3 +1 @@
-module type Chapter2_DeclareVariable = sig
-  val x : int
-end
+val x : int

src/content/1.2/code/ocaml/snippet010.ml

@@ -1 +0,0 @@
-let unit _ = ()

src/content/1.2/code/ocaml/snippet011.ml

@@ -1,3 +0,0 @@
-type bool =
-  | false
-  | true

src/content/1.2/code/ocaml/snippet02.ml

@@ -1,3 +1 @@
-module type Chapter2_DeclareFunction = sig
-  val f : bool -> bool
-end
+val f : bool -> bool

src/content/1.2/code/ocaml/snippet03.ml

@@ -1,3 +1,2 @@
-module Chapter2_Bottom : Chapter2_DeclareFunction = struct
-  let f (b : bool) : bool = failwith "Not Implemented"
-end
+(* val f : bool -> bool *)
+let f _x = failwith "Not Implemented"

src/content/1.2/code/ocaml/snippet04.ml

@@ -1,3 +1,2 @@
-module Chapter2_Bottom : Chapter2_DeclareFunction = struct
-  let f : bool -> bool = fun _ -> failwith "Not implemented"
-end
+(* val f : bool -> bool *)
+let f = failwith "Not Implemented"

src/content/1.2/code/ocaml/snippet05.ml

@@ -1 +1,14 @@
-let fact n = List.fold (List.range 1 n) ~init:1 ~f:( * )
+(* OCaml doesn't ship with a lazy sequence range syntax nor a product
+   function; defining our own. *)
+
+let rec range seq n1 n2 =
+  if n2 < n1 then seq
+  else n2 |> pred |> range (fun () -> Seq.Cons (n2, seq)) n1
+let range = range Seq.empty
+
+let rec product result seq = match seq () with
+  | Seq.Nil -> result
+  | Seq.Cons (n, seq) -> product (result * n) seq
+let product = product 1
+
+let fact n = product (range 1 n)

src/content/1.2/code/ocaml/snippet06.ml

@@ -1,3 +1,2 @@
 type void
-
-let rec absurd (x : void) = absurd x
+val absurd : void -> 'a

src/content/1.2/code/ocaml/snippet07.ml

@@ -1 +1,2 @@
-let f44 () : int = 44
+(* val f44 : unit -> int *)
+let f44 () = 44

src/content/1.2/code/ocaml/snippet08.ml

@@ -1 +1,2 @@
-let f_int (x : int) = ()
+(* val f_int : int -> unit *)
+let f_int x = ()

src/content/1.2/code/ocaml/snippet09.ml

@@ -1 +1,2 @@
-let f_int (_ : int) = ()
+(* val f_int :: int -> unit *)
+let f_int _ = ()

src/content/1.2/code/ocaml/snippet10.ml

@@ -1 +1,2 @@
+(* val unit : 'a -> unit *)
 let unit _ = ()

src/content/1.3/code/ocaml/snippet01.ml

@@ -1,6 +1,6 @@
-module type Monoid = sig
-  type a
+module type MONOID = sig
+  type t
 
-  val mempty : a
-  val mappend : a -> a -> a
+  val mempty : t
+  val mappend : t -> t -> t
 end

src/content/1.3/code/ocaml/snippet02.ml

@@ -1,6 +1,8 @@
-module StringMonoid : Monoid = struct
-  type a = string
+(* In OCaml, any module that defines a module type's members,
+   automatically conforms to that module type. It doesn't need to
+   explicitly declare that it conforms. *)
 
-  let mempty = ""
-  let mappend = ( ^ )
-end
+type t = string
+
+let mempty = ""
+let mappend = ( ^ )

src/content/1.4/code/ocaml/snippet03.ml

@@ -1,7 +1 @@
-module type Kleisli = sig
-  type a
-  type b
-  type c
-
-  val ( >=> ) : (a -> b writer) -> (b -> c writer) -> a -> c writer
-end
+val ( >=> ) : ('a -> 'b writer) -> ('b -> 'c writer) -> 'a -> 'c writer

src/content/1.4/code/ocaml/snippet04.ml

@@ -1 +1,4 @@
-let pure x = x, ""
+let ( >=> ) m1 m2 = fun x ->
+  let y, s1 = m1 x in
+  let z, s2 = m2 y in
+  z, s1 ^ s2

src/content/1.4/code/ocaml/snippet05.ml

@@ -1,3 +1,2 @@
-let up_case : string -> string writer =
- fun s -> String.uppercase s, "up_case "
-;;
+(* val return : 'a -> 'a writer *)
+let return x = x, ""

src/content/1.4/code/ocaml/snippet06.ml

@@ -1,3 +1,6 @@
-let to_words : string -> string list writer =
- fun s -> String.split s ~on:' ', "to_words "
-;;
+(* val up_case : string -> string writer
+   Note: OCaml strings are raw bytestrings, not UTF-8 encoded. *)
+let up_case s = String.uppercase_ascii s, "up_case "
+
+(* val to_words : string -> string list writer *)
+let to_words s = String.split_on_char ' ' s, "to_words "

src/content/1.4/code/ocaml/snippet07.ml

@@ -1,10 +1,2 @@
-module KleisiExample
-    (K : Kleisli
-           with type a = string
-            and type b = string
-            and type c = string list) =
-struct
-  let up_case_and_to_words : string -> string list writer =
-    K.( >=> ) up_case to_words
-  ;;
-end
+(* val process : string -> string list writer *)
+let process = up_case >=> to_words