[Haskell-cafe] type families and type signatures

[Lennart Augustsson]

On Thu, Apr 10, 2008 at 4:20 AM, Manuel M T Chakravarty <
chak at cse.unsw.edu.au> wrote:

> Lennart Augustsson:
>
> > On Wed, Apr 9, 2008 at 8:53 AM, Martin Sulzmann <
> > martin.sulzmann at gmail.com> wrote:
> >
> > Lennart, you said
> >
> > (It's also pretty easy to fix the problem.)
> >
> > What do you mean? Easy to fix the type checker, or easy to fix the
> > program by inserting annotations
> > to guide the type checker?
> >
> > Martin
> >
> > I'm referring to the situation where the type inferred by the type
> > checker is illegal for me to put into the program.
> > In our example we can fix this in two ways, by making foo' illegal even
> > when it has no signature, or making foo' legal even when it has a signature.
> >
> > To make it illegal:  If foo' has no type signature, infer a type for
> > foo', insert this type as a signature and type check again.  If this fails,
> > foo' is illegal.
> >
>
> That would be possible, but it means we have to do this for all bindings
> in a program (also all lets bindings etc).
>

Of course, but I'd rather the compiler did it than I.  It's not that hard,
btw.  If the whole module type checks, insert all signatures and type check
again.

Making it legal might be cheaper, though.

    -- Lennart
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