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A strange example of input in Ocaml

it is rather strange that this fragment of ocaml is well typed toplel. Look at the structure, if g is of type int-> int, as shown at the top level, part of the structure h x = g xwill not be able to get a unified type. So can anyone clarify a little?

module Mymodule : sig
  val h:int ->int
  val g: string-> string
end = struct
  let g x = x
  let h x = g x
end

This is the answer to the topic:

  module Mymodule : sig val h : int -> int val g : string -> string end
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2 answers

It is important to understand that OCaml performs type inference in a compositional style, that is, it first displays the type struct ... end, and only then will it match against the output types sig ... endto make sure that the structure really implements the signature.

For example, if you write

module Monkey : sig val f : int -> int end =
struct
  let f x = x
end

OCaml , , f 'a -> 'a, int -> int. sig ... end Monkey, .. , , f int -> int, .

OCaml , g 'a -> 'a, h 'a -> 'a. , ,

sig val g : 'a -> 'a val h : 'a -> 'a end

. 'a -> 'a int -> int, string -> string OCaml , . , sig ... end , ( ), g h.

, , OCaml:

module Cow =
struct
  let f x = x
  let g x = f [x]
  let a = f "hi"
end

module Bull : sig
  val f : int -> int
  val g : 'b * 'c -> ('b * 'c) list
  val a : string
end = Cow


module Cow :
    sig 
      val f : 'a -> 'a
      val g : 'a -> 'a list
      val a : string
    end

module Bull :
    sig
      val f : int -> int
      val g : 'a * 'b -> ('a * 'b) list
      val a : string end
    end
+7

, string -> string g . ( ) 'a -> 'a. ( : , .)

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