I might have misunderstood your problem, and I do not have a solution pertaining to your exact question,
but hiding the function and its type inside a module argument for a functor does the trick, no ?
For example, if you define

module Foo (M : sig type t val f : t -> t end) =
   struct let use_f x = M.f x end

You can define too modules Foo1 and Foo2 using your different functions.

Marc

2009/11/18 Hans Ole Rafaelsen <hans@simula.no>
Hi,

I have a module that have several functions that take a polymorphic function as part of their arguments (Foo.f1 and Foo.f2 in the example).

module Foo  = struct

 let f1 f =
  f 1

 let f2 f =
  f 1.0

 let f1_ref = (ref (fun _ -> raise (Failure "undefined") : ('a -> 'a) ))
 let set_f1_ref f =
  f1_ref := f

 let f2_ref = (ref (fun _ -> raise (Failure "undefined") : ('a -> 'a) ))
 let set_f2_ref f =
  f2_ref := f

 let use_f1 () =
  !f1_ref 1

 let use_f2 () =
  !f2_ref 1.0

 let internal_f v =
  v

 let internal_f1 () =
  internal_f 1

 let internal_f2 () =
  internal_f 1.0

end

let f v =
 v

let a = Foo.f1 f
let b = Foo.f2 f
let () = Foo.set_f1_ref f
let () = Foo.set_f2_ref f
let c = Foo.use_f1 ()
let d = Foo.use_f2 ()


In my code I don't want to pass this function around to to all functions where Foo.f1 is called. For this reason I would like to store this function that Foo.f1 needs within Foo. (The function is created outside the module and bound with values generated outside the module.) However you can not store polymorphic functions in references. So I have to make one reference for each concrete type it is used for. What I really would like is use it as if it was defined within Foo, like internal_f and used like the internal_f1 and internal_f2.

Is it possible to only store one reference to this kind of function within a module, or do I really have to write a reference for each usage of the function? If I have to create a reference for each case, do anyone have some trick to avoid code repetition?

Regards,

Hans Ole

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