[project @ 2002-11-07 11:42:48 by simonpj]

[project @ 2002-11-07 11:42:48 by simonpj]
------------------
	Fix an obscure bug in implicit parameters,
	interacting with lazy pattern matching
		------------------

		MERGE TO STABLE BRANCH

The problem was this:

  data UniqueSupply = US Integer

  newUnique :: (?uniqueSupply :: UniqueSupply) => Integer
  newUnique = r
            where US r = ?uniqueSupply

The lazy pattern match in the where clause killed GHC 5.04 because the
SourceType {?uniqueSupply::UniqueSupply} of the RHS of the 'where' didn't
look like a UniqueSupply.

The fix is simple: in DsUtils.mkSelectorBinds, use the pattern, not
the rhs, to get the type reqd.  More efficient too.

Test is typecheck/should_compile/tc164.hs