Re: [Caml-list] still silly issues on polymorphic types

[Walter Cazzola <cazzola@dico.unimi.it>]

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Hi all,

On Wed, 28 Sep 2011, Jacques Garrigue wrote:

> On 2011/09/28, at 5:22, Walter Cazzola wrote:
>
>> I still have one problem: how can I assign to a the type 'a list? by
>> using «type a= 'a list» I get
>>
>>  Error: Unbound type parameter 'a
>
> Same thing: you need to make explicit the contents of the list.
> So this can be type a = int list.
> On the other hand if you are trying to refine the signature, you
> can also write
>  type t
>  type a = t list
> keeping t abstract.

thanks for the explanation but I'm still unable to match the 2 types (I
have attached the code again). I get this message:
     # module M0 = Continuation(StringConcat);;
     Error: Signature mismatch:
            Modules do not match:
              sig
                type t = StringConcat.t
                type a = t list
                and b = t
                and c = t list
                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

I have also tried to set the abstract type t to string butwithout any
luck.

     # module M0 = Continuation(StringConcat with StringConcat.t = string) ;;
     Error: Syntax error

I feel myself quite dumb but I can't figure out how to fix it.

Walter

-- 

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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

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

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module StringConcat = struct
  type t
  type a=t list and b=t and c=t list
  let op = fun x y -> y @ [x] ;;
  let init = [] ;;
end