[Caml-list] still silly issues on polymorphic types

[Walter Cazzola]

Dear all,
I'm still playing around with functors, modules and polymorphism but
I've some problems with this last concept.

In the attached files I have tried to implement a sort of function with
a variable number of arguments (based on continuation) and to generalize
the approach I've used a functor (OpVarADT) where I defined the
operation of type 'a -> 'b -> 'c but seems that it is not general enough
to contain int->int->int or 'a -> 'a list -> 'a list

This is the functor instantiation with the errors I get:

  # module M0 = Continuation(StringConcat) ;;
  Error: Signature mismatch:
         Modules do not match:
           sig val op : 'a -> 'a list -> 'a list val init : 'a list end
         is not included in
           OpVarADT.OpVarADT
         Values do not match:
           val op : 'a -> 'a list -> 'a list
         is not included in
           val op : 'a -> 'b -> 'c
  # module M1 = Continuation(Sum) ;;
  Error: Signature mismatch:
         Modules do not match:
           sig val op : int -> int -> int val init : int end
         is not included in
           OpVarADT.OpVarADT
         Values do not match:
           val op : int -> int -> int
         is not included in
           val op : 'a -> 'b -> 'c

I'm sure I'm doing something wrong but I can't see what, any help is
welcome

TIA

Walter

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module Sum = struct
  let op = fun x y -> x+y ;;
  let init = 0 ;;
end

module type OpVarADT = 
 sig
   val op: 'a -> 'b -> 'c
   val init : 'c
 end

module Continuation (OP : OpVarADT.OpVarADT) = 
  struct
    let arg x = fun y continuation -> continuation (OP.op x y) ;;
    let stop x = x;;
    let f g = g OP.init;;
  end

module StringConcat = struct
  let op = fun x y -> y @ [x] ;;
  let init = [] ;;
end