[project @ 2005-11-16 12:55:58 by simonpj]
Two significant changes to the representation of types 1. Change the representation of type synonyms Up to now, type synonym applications have been held in *both* expanded *and* un-expanded form. Unfortunately, this has exponential (!) behaviour when type synonyms are deeply nested. E.g. type P a b = (a,b) f :: P a (P b (P c (P d e))) This showed up in a program of Joel Reymont, now immortalised as typecheck/should_compile/syn-perf.hs So now synonyms are held as ordinary TyConApps, and expanded only on demand. SynNote has disappeared altogether, so the only remaining TyNote is a FTVNote. I'm not sure if it's even useful. 2. Eta-reduce newtypes See the Note [Newtype eta] in TyCon.lhs If we have newtype T a b = MkT (S a b) then, in Core land, we would like S = T, even though the application of T is then not saturated. This commit eta-reduces T's RHS, and keeps that inside the TyCon (in nt_etad_rhs). Result is that coreEqType can be simpler, and has less need of expanding newtypes.
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