Update OCaml snippets

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 (* In a module signature *)

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 (* In a module signature *)

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

@@ -1,9 +1,7 @@
-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)
+Fun.compose g f (* Since OCaml 5.2 *)
 
-  let compose : 'a -> 'c = G.g >> F.f
-end
+(* Alternatively, you can also define it as follows: *)
+let compose f g x = f (g x)
+
+(* Or even as an infix operator: *)
+let ( % ) = Fun.compose (* Like in the Batteries library *)

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

@@ -1,9 +1,6 @@
-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
-
-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
+(* Assuming these signatures *)
+val f : a -> b
+val g : b -> c
+val h : c -> d
+(* These are equivalent *)
+h % (g % f) = (h % g) % f = h % g % f

src/content/1.1/code/ocaml/snippet05.ml

@@ -1 +1,2 @@
-let id x = x
+(* val id : 'a -> 'a *)
+let id x = x (* Also defined as Fun.id in the Stdlib *)

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

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

src/content/1.10/code/ocaml/snippet01.ml

@@ -1 +1 @@
-val alpha : 'a . 'a f -> 'a g
+val alpha : 'a . 'a F.t -> 'a G.t (* For 2 Functors F and G *)

src/content/1.10/code/ocaml/snippet02.ml

@@ -1 +1 @@
-val alpha : 'a f -> 'a g
+val alpha : 'a F.t -> 'a G.t (* For 2 Functors F and G *)

src/content/1.10/code/ocaml/snippet03.ml

@@ -1 +1 @@
-val alpha : 'a f -> 'a g
+val alpha : 'a F.t -> 'a G.t

src/content/1.10/code/ocaml/snippet04.ml

@@ -1,4 +1,3 @@
 let safe_head = function
   | [] -> None
   | x :: xs -> Some x
-;;

src/content/1.10/code/ocaml/snippet05.ml

@@ -1 +1,3 @@
-compose (fmap f) safe_head = compose safe_head (fmap f)
+(* Given a Functor implementation for Option and List,
+   the following equality should hold: *)
+OptionFunctor.fmap f % safe_head = safe_head % ListFunctor.fmap f

src/content/1.10/code/ocaml/snippet06.ml

@@ -1,2 +1,4 @@
-(* Starting with empty list *)
-let fmap f (safe_head []) = fmap f None = None
+(* As a reminder, this is not actual code *)
+OptionFunctor.fmap f (safe_head [])
+  = OptionFunctor.fmap f None
+  = None

src/content/1.10/code/ocaml/snippet07.ml

@@ -1 +1 @@
-let safe_head (fmap f []) = safe_head [] = None
+safe_head (ListFunctor.fmap f []) = safe_head [] = None

src/content/1.10/code/ocaml/snippet08.ml

@@ -1 +1,3 @@
-let fmap f (safe_head (x :: xs)) = fmap f (Some x)= Some (f x)
+OptFunctor.fmap f (safe_head (x :: xs))
+  = OptFunctor.fmap f (Some x)
+  = Some (f x)

src/content/1.10/code/ocaml/snippet09.ml

@@ -1 +1,4 @@
-let safe_head (fmap f (x :: xs)) = safe_head (f x :: f xs) = Some (f x)
+
+safe_head (ListFunctor.fmap f (x :: xs))
+  = safe_head (f x :: f xs)
+  = Some (f x)

src/content/1.10/code/ocaml/snippet10.ml

@@ -1,4 +1,6 @@
-let rec fmap f = function
-  | [] -> []
-  | x :: xs -> f x :: fmap f xs
-;;
+module ListFunctor : Functor with type 'a t = 'a list = struct
+  type 'a t = 'a list
+  let rec fmap f = function
+    | [] -> []
+    | x :: xs -> f x :: fmap f xs
+end

src/content/1.10/code/ocaml/snippet11.ml

@@ -1,4 +1,14 @@
-let rec fmap f = function
-  | None -> None
-  | Some x -> Some (f x)
-;;
+module OptionFunctor : Functor with type 'a t = 'a option = struct
+  type 'a t = 'a option
+
+  let fmap f = function
+      | None -> None
+      | Some x -> Some (f x)
+end
+
+(* As a reminder, note that in the OCaml Stdlib, the List
+   and Option modules are already "Functors" in the sense
+   that they have an fmap function (called map). Thus, the
+   following fmaps do the same as the fmaps defined above. *)
+let option_fmap f = Option.map f
+let list_fmap f = List.map f

src/content/1.10/code/ocaml/snippet12.ml

@@ -1,8 +1,6 @@
-(** OCaml requires mutually recursive functions to be defined together *)
+type ('c, 'a) const = Const of 'c
+
+(* Assuming you've defined un_const before this function *)
 let rec length : 'a list -> (int, 'a) const = function
   | [] -> Const 0
   | _ :: xs -> Const (1 + un_const (length xs))
-
-and un_const : 'c 'a. ('c, 'a) const -> 'c = function
-  | Const c -> c
-;;

src/content/1.10/code/ocaml/snippet13.ml

@@ -1,3 +1 @@
-let un_const : 'c 'a. ('c, 'a) const -> 'c = function
-  | Const c -> c
-;;
+let un_const (Const c) = c

src/content/1.10/code/ocaml/snippet15.ml

@@ -1,3 +1 @@
-let scam : 'a. ('int, 'a) const -> 'a option = function
-  | Const a -> None
-;;
+let scam (Const x : (int, 'a) const) : 'a option = None

src/content/1.10/code/ocaml/snippet17.ml

@@ -1,10 +1,7 @@
 module Reader_Functor (T : sig
   type e
-end) : Functor = struct
+end) : Functor with type 'a t = (T.e, 'a) reader = struct
   type 'a t = (T.e, 'a) reader
 
-  let fmap : 'a 'b. ('a -> 'b) -> 'a t -> 'b t =
-   fun f -> function
-    | Reader r -> Reader (compose f r)
- ;;
+  let fmap f (Reader g) = Reader (fun e -> f (g e))
 end

src/content/1.10/code/ocaml/snippet19.ml

@@ -1,3 +1 @@
-let dumb : 'a. (unit, 'a) reader -> 'a option = function
-  | Reader _ -> None
-;;
+let dumb (Reader _) = None

src/content/1.10/code/ocaml/snippet20.ml

@@ -1,3 +1 @@
-let obvious : 'a. (unit, 'a) reader -> 'a option = function
-  | Reader f -> Some (f ())
-;;
+let obvious (Reader g) = Some (g ())

src/content/1.10/code/ocaml/snippet22.ml

@@ -1,10 +1,7 @@
 module Op_Contravariant (T : sig
   type r
-end) : Contravariant = struct
+end) : Contravariant with type 'a t = (T.r, 'a) op = struct
   type 'a t = (T.r, 'a) op
 
-  let contramap : ('b -> 'a) -> 'a t -> 'b t =
-   fun f -> function
-    | Op g -> Op (compose g f)
- ;;
+  let contramap f (Op g) = Op (Fun.compose g f)
 end

src/content/1.10/code/ocaml/snippet23.ml

@@ -1,3 +1 @@
-let pred_to_str = function
-  | Op f -> Op (fun x -> if f x then "T" else "F")
-;;
+let pred_to_str (Op f) = Op (fun x -> if f x then "T" else "F")

src/content/1.10/code/ocaml/snippet24.ml

@@ -1 +1 @@
-compose (contramap f) pred_to_str = compose pred_to_str (contramap f)
+contramap f % pred_to_str = pred_to_str % contramap f

src/content/1.10/code/ocaml/snippet25.ml

@@ -4,4 +4,3 @@ end)
 
 let op_bool_contramap : ('b -> 'a) -> 'a Op_Bool.t -> 'b Op_Bool.t =
   Op_Bool.contramap
-;;

src/content/1.10/code/ocaml/snippet27.ml

@@ -1 +1 @@
-('a -> 'a) -> 'a f
+('a -> 'a) -> 'a F.t

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

@@ -1,3 +1,3 @@
 module Chapter2_Bottom : Chapter2_DeclareFunction = struct
-  let f : bool -> bool = fun _ -> failwith "Not implemented"
+  let f : bool -> bool = failwith "Not implemented"
 end

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

@@ -1 +1 @@
-let fact n = List.fold (List.range 1 n) ~init:1 ~f:( * )
+let fact n = Seq.(fold_left ( * ) 1 (take n (ints 1)))

src/content/1.2/code/ocaml/snippet11.ml

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

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

@@ -1,6 +1,6 @@
 module type Monoid = sig
-  type a
+  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

@@ -1,5 +1,5 @@
-module StringMonoid : Monoid = struct
-  type a = string
+module StringMonoid : Monoid with type t = string = struct
+  type t = string
 
   let mempty = ""
   let mappend = ( ^ )

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

@@ -1,7 +1,4 @@
-module type Kleisli = sig
-  type a
-  type b
-  type c
-
-  val ( >=> ) : (a -> b writer) -> (b -> c writer) -> a -> c writer
+module type Fish_sig = sig
+  val ( >=> ) : ('a -> 'b writer) ->
+                ('b -> 'c writer) -> 'a -> 'c writer
 end

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

@@ -1 +1,5 @@
-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 @@
-let up_case : string -> string writer =
- fun s -> String.uppercase s, "up_case "
-;;
+let return x = (x, "")

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

@@ -1,3 +1,5 @@
-let to_words : string -> string list writer =
- fun s -> String.split s ~on:' ', "to_words "
-;;
+let up_case (s : string) : string writer =
+  (String.uppercase_ascii s, "up_case ")
+
+let to_words (s : string) : string list writer =
+  (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
+let process : string -> string list writer =
+  up_case >=> to_words

src/content/1.5/code/ocaml/snippet02.ml

@@ -1 +1 @@
-let unit x = ()
+let unit _ = ()

src/content/1.5/code/ocaml/snippet05.ml

@@ -1,2 +1,2 @@
-compose f g = id
-compose g f = id
+Fun.compose f g = Fun.id
+Fun.compose g f = Fun.id

src/content/1.5/code/ocaml/snippet10.ml

@@ -1,8 +1,4 @@
-module Chapter5_Product_Example :
-  Chapter5_Product
-    with type a = int
-     and type b = bool
-     and type c = int = struct
+module Chapter5_Product_Example : Chapter5_Product = struct
   type a = int
   type b = bool
   type c = int

src/content/1.5/code/ocaml/snippet12.ml

@@ -1,2 +1,2 @@
-let p' = compose Chapter5_Product_Example.p m
-let q' = compose Chapter5_Product_Example.q m
+let p' = Fun.compose Chapter5_Product_Example.p m
+let q' = Fun.compose Chapter5_Product_Example.q m

src/content/1.5/code/ocaml/snippet13.ml

@@ -1 +1 @@
-let m (x : int) = x, true
+let m (x : int) : int * bool = x, true

src/content/1.5/code/ocaml/snippet14.ml

@@ -1,2 +1,2 @@
-let p x = fst (m x)
-let q x = snd (m x)
+let p x = fst (m x) (* = x *)
+let q x = snd (m x) (* = true *)

src/content/1.5/code/ocaml/snippet16.ml

@@ -1,2 +1,2 @@
-fst = compose p m'
-snd = compose q m'
+let fst = Fun.compose p m'
+let snd = Fun.compose q m'

src/content/1.5/code/ocaml/snippet22.ml

@@ -1,2 +1,2 @@
-i' == compose m i
-j' == compose m j
+let i' = Fun.compose m i
+let j' = Fun.compose m j

src/content/1.5/code/ocaml/snippet23.ml

@@ -1,3 +1 @@
-type contact =
-  | PhoneNum of int
-  | EmailAddr of string
+type contact = PhoneNum of int | EmailAddr of string

src/content/1.5/code/ocaml/snippet24.ml

@@ -1 +1 @@
-let helpdesk = PhoneNum 2222222
+let helpdesk : contact = PhoneNum 2222222

src/content/1.5/code/ocaml/snippet25.ml

@@ -1,3 +1,2 @@
-type ('a, 'b) either =
-  | Left of 'a
-  | Right of 'b
+(* Available in the [Either] module of the Stdlib *)
+type ('a, 'b) either = Left of 'a | Right of 'b

src/content/1.5/code/ocaml/snippet26.ml

@@ -1,4 +1,3 @@
 let factorizer i j = function
   | Left a -> i a
   | Right b -> j b
-;;

src/content/1.5/code/ocaml/snippet27.ml

@@ -1,2 +1,2 @@
-p = compose fst m
-q = compose snd m
+let p = Fun.compose fst m
+let q = Fun.compose snd m

src/content/1.5/code/ocaml/snippet28.ml

@@ -1,2 +1,2 @@
-p () = fst (m ())
-q () = snd (m ())
+let p () = fst (m ())
+let q () = snd (m ())

src/content/1.6/code/ocaml/snippet12.ml

@@ -1 +1,2 @@
-let stmt = "This statement is", false
+(* You cannot do that in OCaml *)
+let stmt = ("This statement is", false)

src/content/1.6/code/ocaml/snippet14.ml

@@ -1,3 +1,2 @@
 let starts_with_symbol (name, symbol, _) =
-  String.is_prefix name ~prefix:symbol
-;;
+  String.starts_with ~prefix:symbol name

src/content/1.6/code/ocaml/snippet16.ml

@@ -1,3 +1,2 @@
 let tuple_to_elem (name, symbol, atomic_number) =
   { name; symbol; atomic_number }
-;;

src/content/1.6/code/ocaml/snippet17.ml

@@ -1,3 +1,2 @@
 let elem_to_tuple { name; symbol; atomic_number } =
   name, symbol, atomic_number
-;;

src/content/1.6/code/ocaml/snippet19.ml

@@ -1,3 +1,2 @@
 let starts_with_symbol { name; symbol; _ } =
-  String.is_prefix name ~prefix:symbol
-;;
+  String.starts_with ~prefix:symbol name

src/content/1.6/code/ocaml/snippet20.ml

@@ -1,2 +1,2 @@
 (* OCaml only allows special characters in the infix operator.
-   So, the above function name cannot be applied be infix. *)
+   So, the above function name cannot be made infix. *)

src/content/1.6/code/ocaml/snippet21.ml

@@ -1,3 +1,2 @@
-type ('a, 'b) either =
-  | Left of 'a
-  | Right of 'b
+(* Available in the [Either] module of the Stdlib *)
+type ('a, 'b) either = Left of 'a | Right of 'b

src/content/1.6/code/ocaml/snippet23.ml

@@ -1 +1 @@
-'a void either
+('a, void) Either.t

src/content/1.6/code/ocaml/snippet24.ml

@@ -1,4 +1 @@
-type color =
-  | Red
-  | Green
-  | Blue
+type color = Red | Green | Blue

src/content/1.6/code/ocaml/snippet25.ml

@@ -1,3 +1 @@
-type bool =
-  | True
-  | False
+type bool = True | False