-Wall and the fail method

Nikita Karetnikov nikita at karetnikov.org
Fri May 22 10:06:37 UTC 2015

Can -Wall be extended to report pattern match failures in do
expressions, like it does for case expressions?

Prelude> :set -Wall
Prelude> let f = do Just x <- return Nothing; return x
Prelude> let g = case Nothing of Just x -> x

<interactive>:9:9: Warning:
    Pattern match(es) are non-exhaustive
    In a case alternative: Patterns not matched: Nothing

One can argue that it's similar to undefined, error, and various
unsafeSomething functions, which I think should be reported as well, if
possible.  But these things can be found already with a simple grep
while a pattern match cannot.

I bet it has been discussed already, but "fail" is a terrible search
term, so I cannot find anything relevant in the archives nor in the bug

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