Hello everyone, to my dismay, a -Wall compiled program I deployed today crashed with Exception: Non-exhaustive patterns in lambda and I learned from http://dev.stephendiehl.com/hask/ that A more subtle case is when implicitly pattern matching with a single "uni-pattern" in a lambda expression. The following will fail when given a Nothing. boom = \(Just a) -> something GHC can warn about these cases with the -fwarn-incomplete-uni-patterns flag. And in fact: ghci -Wall
map (\Nothing -> "ok") [Just 'a'] ["*** Exception: <interactive>:2:6-21: Non-exhaustive patterns in lambda :set -fwarn-incomplete-uni-patterns map (\Nothing -> "ok") [Just 'a'] <interactive>:4:6: Warning: Pattern match(es) are non-exhaustive
It really surprised me that -fwarn-incomplete-uni-patterns is not included in -Wall; I've felt really safe with my -Wall so far, especially about totality and similar things that will almost certainly lead to crashes. In an older mail from 2010 (https://mail.haskell.org/pipermail/glasgow-haskell-users/2010-September/0192...) I saw Simon mention that it wasn't planned to warn about inexhaustive patterns like this. I feel like there has been a strong push towards more totality in the last years, and I would like to ask if enabling -fwarn-incomplete-uni-patterns in -Wall may be reconsidered for a coming next GHC version, or if there are still opponents to that. Niklas