OCaml signature dependencies error

Question

I have the following module signature A :

module type A =
 sig
  type exp =
    Int of int
    | Var of string
end;;

which I am able to compile in order to get a.mli and a.cmi files. However, if I define B :

module type B =
 sig
  val compute : A.exp -> A.exp
 end;;

running ocamlc -i b.ml produces the error Unbound type constructor A.exp . Why is that?

Answer 1

OCaml gives you an outer module for free, corresponding to each source file. So you are defining a module type named AA Note that it's a module type , not a module.

It's possible your a.ml (and a.mli if you like) should contain just the following:

type exp = Int of int | Var of string

Then you can refer to A.exp from your b.ml file.

Also, note that a.mli is a source file. If you have an a.mli file, you need to compile it to create a.cmi.