stupid sourceforge...
On 7/25/07, Erick Tryzelaar <[EMAIL PROTECTED]> wrote:
> So I decided the best way to learn about arrows is to try to implement
> them. However, I'm running into some problems. I've got the
> preliminary typeclass implemented here:
>
> #import <flx.flxh>
>
> fun swap[A, B] (a:A, b:B): (B*A) => (b, a);
>
> typeclass Arrow[M: TYPE->TYPE->TYPE]
> {
> virtual fun arrow[a, b]: (a->b) -> M a b;
> virtual fun bind[a, b, c]: M a b -> M b c -> M a c;
> virtual fun first[a, b, c]: M a b -> M (a*c) (b*c);
> virtual fun second[a, b, c]: M a b -> M (c*a) (c*b);
>
> virtual fun foo[a, b, c] (f:M a b): M (a*c) (c*a) =>
> arrow (the swap[a, c])
> ;
> }
>
> But felix doesn't like this, and reports this:
>
> //Parsing Implementation std.flx
> //Parsing Implementation main.flx
> Questionable meta typing of term: <T4563> * <T4565>
> Questionable meta typing of term: <T4577> * <T4575>
> Questionable meta typing of term: <T4587> * <T4589>
> CLIENT ERROR
> In return (arrow the swap[a, c]);
> Wrong return type,
> expected : (<T4537:(TYPE 0 -> (TYPE 0 -> TYPE 0))> (<T4587> *
> <T4589>)) (<T4589> * <T4587>)
> but we got (<T4537> (<T4587> * <T4589>)) (<T4589> * <T4587>)
> In ./main.flx: line 12 col 3 to line 14 col 3
> 11:
> 12: virtual fun foo[a, b, c] (f:M a b): M (a*c) (c*a) =>
> 13: arrow (the swap[a, c])
> 14: ;
> 15: }
>
>
>
> There are three things I see here. First, why is this type
> questionable? It'd be a little easier to read the return type if my
> named abstract types were used instead of the <T4563> style names. Not
> sure how practical that is though. Third, aren't these the same times?
>
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