GHC tries to do so, but sometimes gets it wrong. See the
-fwarn-incomplete-patterns flag. We'd appreciate it if
someone could
overhaul this code - it's been on the wish list for a long time.
Indeed, I always try to avoid all warnings in my sources by using the flag "-Wall", because I consider this to be good programming style. (In particular warnings about unused and shadowed variables prevented a lot of errors.) However some warnings are difficult to avoid. So how difficult would it be to implement non-exhaustive pattern warnings for nested patterns?
data Color = Red | Green | Blue
f :: Color -> String
f x = case x of
Red -> "r"
_ -> " " ++ case x of
Green -> "g"
Blue -> "b" Warning: Pattern match(es) are non-exhaustive
In a case alternative: Patterns not matched: Red"Red" in the second case is unreachable (and this should also be worth a warning.)
Christian
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