Re: [Caml-list] A weird typing error

[Philippe Wang <mail@philippewang.info>]

Hi,

I re-wrote your program, twice.

First time: The actual problem was submerged... so I removed the
irrelevant code.
It became:

type 'a twice = 'a
class map = object ((self : 'self_type))
  method twice : 'a0 'b0. ('self_type -> 'a0 -> 'b0) -> 'a0 twice -> 'b0 twice =
    fun mf_a -> mf_a self
end

=> ocamlc points a surprising error at line 1. I don't quite understand...

Second time: well, line 1 seems fine to me. I added some missing parameters.
It became:

type 'a twice = 'a
class map =
object ((self : 's))
  method twice : 'a0 'b0. ('s -> 'a0 -> 'b0) -> 'a0 twice -> 'b0 twice =
    fun mf_a x -> mf_a (self : 's)  (x: 'a0 twice)
end

=> ocamlc points the same error, but at line 5, which is a lot better,
much less weird...
Well, kind of same error: the weird (buggy) part of the message is
removed, the important part is kept.


And now... I just don't know why it doesn't type-check. All I have
left to say is that I hate encoding data into type names. It's fun
when it works. It's hell otherwise.

I'm curious to understand the solution of this weird problem, if
someone unravels it.

Cheers.
Philippe Wang



On Thu, May 24, 2012 at 7:55 PM, bob zhang <bobzhang1988@gmail.com> wrote:
>
> Hi, list
>     I came across a weird type error.
>     The error message is  "Error: The implementation type_error_ppo.ml
>        does not match the interface (inferred signature):"
>     I attached the file
>    Many thanks
>
> --
> -- Bob