• Simon Peyton Jones's avatar
    [project @ 2002-02-07 12:51:34 by simonpj] · 20f50b2a
    Simon Peyton Jones authored
    	Make TcType.match and TcUnify.uUnboundVar kind-aware
    George Russel had apparently-overlapping (ha) instance decls like
    	instance .. => C (a b) where
    	instance .. => C (x y) where
    But the a,b and x,y were different kinds!  Turned out that TcType.unify
    was kind-aware (so we didn't report a duplicate instance decl, but TcType.match
    was not (so we simply selected the wrong one, and got a mis-kinded constraint
    popping up from the ".."  part.  Very exciting to track down.
    I also make the ordinary unification kind-aware in the same way.  It's
    quite legitimate to attempt to unify, say,
    	(a b)    with     (c d)
    but the unification should fail if a's kind differs from c's.
    (There was a kind of debug warning before, but it's actually not an error
    in the compiler... so it should just make unification fail gracefully.)