[Caml-list] A weird typing error

[Caml-list] A weird typing error

[bob zhang]

[-- Attachment #1.1: Type: text/plain, Size: 228 bytes --]

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

[-- Attachment #1.2: Type: text/html, Size: 415 bytes --]

[-- Attachment #2: type_error_ppo.ml --]
[-- Type: application/octet-stream, Size: 1324 bytes --]

type 'a m_list = | M_nil | M_cons of 'a * 'a m_list

type 'a twice = 'a

type 'a tree =
  | Leaf | Node of ('a tree) m_list * (('a tree) m_list) twice * 'a

class base =
  object method int : int -> int = fun x -> x
    method float : float -> float = fun x -> x
    method string : string -> string = fun x -> x
  end
  
module EQ =
  struct
    class map =
      object ((self : 'self_type))
        inherit base
        method unknown : 'a. 'a -> 'a = fun x -> x
        method tree :
          'a0 'b0. ('self_type -> 'a0 -> 'b0) -> 'a0 tree -> 'b0 tree =
          fun mf_a ->
            function
            | Leaf -> Leaf
            | Node (a0, a1, a2) ->
                Node ((self#m_list (fun self -> self#tree mf_a) a0),
                  (self#twice
                     (fun self -> self#m_list (fun self -> self#tree mf_a))
                     a1),
                  (mf_a self a2))
        method twice :
          'a0 'b0. ('self_type -> 'a0 -> 'b0) -> 'a0 twice -> 'b0 twice =
          fun mf_a -> mf_a self
        method m_list :
          'a0 'b0. ('self_type -> 'a0 -> 'b0) -> 'a0 m_list -> 'b0 m_list =
          fun mf_a ->
            function
            | M_nil -> M_nil
            | M_cons (a0, a1) ->
                M_cons ((mf_a self a0), (self#m_list mf_a a1))
      end
      
  end
  

Re: [Caml-list] A weird typing error

[Philippe Wang]

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

Re: [Caml-list] A weird typing error

[Jonathan Protzenko]

FWIW it type-checks on a recent trunk build.

jonathan

On Fri 25 May 2012 12:17:33 AM CEST, Philippe Wang wrote:
> 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
>