Fri Dec 11 04:01:22 PST 2009 [email protected]
* Fix two related bugs in u_tys
Ignore-this: 25e826e0915c6f6267cadff96f1d7ca6
When we normalise a type family application we must recursively call
uTys, *not* 'go', because the latter loop is only there to look
through type synonyms. This bug made the type checker generate
ill-typed coercions, which were rejected by Core Lint.
A related bug only affects the size of coercions. If faced with
(m a) ~ (F b c)
where F has arity 1, we want to decompose to
m ~ F Int, a ~ c
rather than deferring. The application decomposition was being
tried last, so we were missing this opportunity.
Thanks to Roman for an example that showed all this up.
M ./compiler/typecheck/TcUnify.lhs -23 +24
View patch online:
http://darcs.haskell.org/ghc/_darcs/patches/20091211120122-1287e-c1f5791d4b503d1da4bab7d9d9b7f8d1f09fce79.gz
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