Excerpts from Jacques Le Normand's message of Sun Dec 20 18:44:57 +0100 2009:
> Dear ocaml-list,
> the following code does not type check:
>
> type foo = {bar : 'a. 'a -> 'a}
> let a : int -> int = fun x -> x
> let baz = {bar = Obj.magic a}
>
> with the error
>
> Error: This field value has type 'a -> 'a which is less general than
> 'b. 'b -> 'b
>
>
> my question is: how could I use obj.magic to get a polymorphic type?
Apart from the traditional
"You should avoid Obj.magic as much as possible!"
I once faced this situation and the solution is to use modules.
module M : sig
val f : 'a -> 'a
end = struct
let f = Obj.magic
end ;;
let baz = {bar = M.f };;
Have fun!
--
Nicolas Pouillard
http://nicolaspouillard.fr
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