type inference bug

[Jeffrey R Lewis]

On Wednesday, March 5, 2003, at 05:00 PM, Mark Tullsen wrote:

> Here's a (serious) bug in the type-inferencer of the November 2002 
> Hugs (tested
> using hugs98-Nov2002-rh7.3-1.i386.rpm):
>
>   data T a b = T {f1 :: a, f2 :: b}
>   updateF1 x t = t{f1 = x}
>
>   the type inferred for updateF1:
>     observed behavior:
>       updateF1 :: a -> T b c -> T a d
>     expected behavior:
>       updateF1 :: a -> T b c -> T a c
>
> FYI, this bug didn't exist in the Dec 2001 version.
>

Mark:

     Slurp in a fresh version from CVS.  I suspect that's the bug I 
introduced, and was kindly spotted and fixed by Ross Patterson.

--Jeff