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  • #8494

Closed
Open
Opened Nov 01, 2013 by JohnWiegley@trac-JohnWiegley

Warn if a pattern guard obviates all others

The following code, when compiled with -Wall, gives no warnings:

module Main where

main :: IO ()
main = print $ foo (10 :: Int)
  where
    foo x
        | True = (20 :: Int)
        | x == 10 = (30 :: Int)

I would expect that since the pattern guard | True obviates the following guards, that it would warn about unreachable code. There was a bug in my code today which I tracked down to a code transposition that would have been easily spotted with such a warning.

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Version 7.6.3
Type FeatureRequest
TypeOfFailure OtherFailure
Priority normal
Resolution Unresolved
Component Compiler
Test case
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Reference: ghc/ghc#8494