patch applied (ghc): Fix Trac #1899; missing equality check in typechecker's constraint simplifier

[Simon Peyton Jones]

Tue Feb 26 09:47:43 PST 2008  simonpj at microsoft.com
  * Fix Trac #1899; missing equality check in typechecker's constraint simplifier
  
  This patch fixes a missing equality check (uifying type variable b=b) in
  the new constraint simplifier in TcTyFuns.  As it stands, we were making
  'b' point to itself, which subsequently led to an infinite loop when
  zonking.  Test is T1899.hs
  
  
  

    M ./compiler/typecheck/TcTyFuns.lhs -11 +16