Question

Can I disable the non-exhaustive pattern matches warning only for lambdas?

I like the warning in general, but not for actual lambda literals like this:

map (\(x:xs)->...) ls

I think this code makes it pretty clear that I expect all the values of ls to always have at least one element, and there is no neat way to handle the error case in the lambda. (I guess I could move the pattern match into a case statement, but that would just be ugly.)

Answer 1

Yes, but only in GHC 7.2 onwards; pass -fno-warn-incomplete-uni-patterns (e.g. in your Cabal file’s ghc-options field, or in an {-# OPTIONS_GHC #-} pragma at the top of your file).

However, this will also disable the warning for pattern bindings, so let Just x = Nothing in x won’t produce a warning. case statements are unaffected.