patch applied (ghc): Fix pre-subsumption and pre-matching
Simon Peyton Jones
simonpj at microsoft.com
Tue Aug 8 05:15:37 EDT 2006
Tue Aug 8 02:11:08 PDT 2006 simonpj at microsoft.com
* Fix pre-subsumption and pre-matching
The pre-subsuption and pre-matching functions should NEVER make bogus
bindings of type variables, although they are free to bale out and make
too few bindings.
I hadn't been thiking carefully enough about this, and there were two
- Firstly, in pre-subsumption we must ignore the 'theta'
part of any overloaded type.
- Second, in pre-matching, we must return the empty subustition
on a mis-match, rather than returning the substitution so far.
This bug showed up when compiling Data.Generics.Schemes.hs, and is
imortalised in test tc206
M ./compiler/typecheck/TcUnify.lhs -6 +24
More information about the Cvs-ghc