[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.

1 files changed, 0 insertions, 1 deletions

diff --git a/ghc/compiler/codeGen/ClosureInfo.lhs b/ghc/compiler/codeGen/ClosureInfo.lhs
index 48c4ddeda8..b0e9e232d7 100644
--- a/ghc/compiler/codeGen/ClosureInfo.lhs
+++ b/ghc/compiler/codeGen/ClosureInfo.lhs
@@ -946,7 +946,6 @@ getTyDescription ty
       FunTy _ res      	     -> '-' : '>' : fun_result res
       TyConApp tycon _ 	     -> getOccString tycon
       NoteTy (FTVNote _) ty  -> getTyDescription ty
-      NoteTy (SynNote ty1) _ -> getTyDescription ty1
       PredTy sty	     -> getPredTyDescription sty
       ForAllTy _ ty          -> getTyDescription ty
     }