Yes, this is a nuisance, esp because ghc can most of the time see perfectly
well that if you *do* write down the "missing" cases that they are
inaccessible. There are a bunch of open tickets about it. I too use
Richard's trick; I tend to use
foo _ _ = error "inaccessible"
Fixing ghc so that it can always see that clauses are not actually missing
might be difficult; perhaps the solution adopted in Agda would be easier,
where you would write
foo (SomeConstructor _) (SomeOtherConstructor _) ()
(where SomeConstructor and SomeOtherConstructor are the "missing" cases) to
indicate that "this is inaccessible pattern".
-E
On Mon, May 19, 2014 at 12:45 AM, Richard Eisenberg
The short answer here (to "Is there a way to avoid the non-exhaustive pattern-match warning?") is "no, not in general". See #3927 ( https://ghc.haskell.org/trac/ghc/ticket/3927).