Monomorphism restriction in classes

Monomorphism restriction in classes

[Christian Stork]

So, what's the best work-around for this problem?

class c (len : 'a list -> int) =
object 
  method str_len (l: string list) = len l
  method int_len (l: int list)    = len l
end

$ ocamlc monoRestForClasses.ml 
File "monoRestForClasses.ml", line 7, characters 40-41:
This expression has type int list but is here used with type string list
 
Thanks,
Chris

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Re: [Caml-list] Monomorphism restriction in classes

[Gerd Stolpmann]

Am Freitag, den 17.02.2006, 13:09 -0800 schrieb Christian Stork:
> So, what's the best work-around for this problem?
> 
> class c (len : 'a list -> int) =
> object 
>   method str_len (l: string list) = len l
>   method int_len (l: int list)    = len l
> end
> 

type len_t = { len : 'a . 'a list -> int}

class c (len :len_t) =
object
  method str_len (l:string list) = len.len l
  method int_len (l: int list) = len.len l
end

I don't know why the 'a.t syntax is only allowed for records and
methods, and why one cannot say

class c (len : 'a . 'a list -> int) = ...

Gerd

> $ ocamlc monoRestForClasses.ml 
> File "monoRestForClasses.ml", line 7, characters 40-41:
> This expression has type int list but is here used with type string list
>  
> Thanks,
> Chris
> 
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