Incomplete-pattern checking for n+k patterns is not implemented

The check for incomplete patterns does not understand about n+k patterns. Here's an example:

f 0     = True
f (n+1) = False

GHC says, rather confusingly:

    Warning: Pattern match(es) are non-exhaustive
	     In the definition of `f':
		 Patterns not matched: #x with #x `notElem` [0#]

The reason is in compiler/deSugar/Check.hs which says

	-- Horrible hack.  The simplify_pat stuff converts NPlusK pats to WildPats
	-- which of course loses the info that they can fail to match.  So we 
	-- stick in a CanFail as if it were a guard.
	-- The Right Thing to do is for the whole system to treat NPlusK pats properly

See #595 (closed)

Trac metadata

Trac field	Value
Version	6.4.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
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Blocking
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Operating system	Unknown
Architecture	Unknown