[project @ 2004-11-11 15:14:53 by simonpj]

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testsuite/tests/ghc-regress/typecheck/should_fail/tcfail080.hs

@@ -2,6 +2,17 @@
 
 -- !!! Multi-param type classes test: ambiguity bug
 
+-- GHC actually accepts this program because
+--	q :: Collection c a => a -> Bool
+-- and there is no a priori reason to suppose that
+-- q would be ambiguous in every context. For example,
+-- it could be fine if we had
+--	instance c Int where ...
+-- Of course, it'd be hard to fill in the "..." in this particular
+-- case, but that relies on observations about the form of the types
+-- of the class methods, surely beyond what a compiler should do.
+-- That's why GHC accepts it
+
 module ShouldFail where
 
 class Collection c a where