[project @ 2001-12-03 11:36:26 by simonpj]

[project @ 2001-12-03 11:36:26 by simonpj]
------------------------------------
	Fix a tiresome and longstanding bug
	in typechecking of unlifted bindings
	------------------------------------

Consider

	data T = MkT Int# Int#

	f :: T -> Int#
	f t = a +# b
	    where
	      MkT a b = if ... then t else t

This should really be OK, but if the "..." includes
some constraints, the constraint simplifier was trying to
generate some d1=d2 bindings. This is Bad because the desugarer
treats unlifted bindings very specially (they are strict).

This commit fixes the problem, by ensuring we never get
local dictionary binding for an unlifted group.

This fixes the bug which has been making the Alpha port fall
over with a pattern-match failure in DsExpr.  Nothing to do
with Alpha; it's just that the word-size change gave rise
to a little more commoning-up of literals in the type checker
which in turn made the desugarer it fall over.