[project @ 2001-06-11 12:24:51 by simonpj]

[project @ 2001-06-11 12:24:51 by simonpj]
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	Tidy up and improve "pattern contexts"
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In various places (renamer, typechecker, desugarer) we need to know
what the context of a pattern match is (case expression, function defn,
let binding, etc).  This commit tidies up the story quite a bit.  I
think it represents a net decrease in code, and certainly it improves the
error messages from:

	f x x = 3

Prevsiously we got a message like "Conflicting bindings for x in a pattern match",
but not it says "..in a defn of function f".

WARNING: the tidy up had a more global effect than I originally expected,
so it's possible that some other error messages look a bit peculiar.  They
should be easy to fix, but tell us!