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Bang patterns in do-notation and lambdas need parentheses around them to parse. This isn't the case for ~ patterns, or bang patterns in let bindings. Seems like a wibble.

{-# OPTIONS -fbang-patterns #-}

-- doesn't work:        A.hs:5:8: Empty 'do' construct
main1 = do
    !c <- return ()
    return ()

-- doesn't work:        A.hs:12:24: parse error on input `!'
main2 = return () >>= \ !c -> return ()



-- does
main3 = do
    (!c) <- return ()
    return ()

-- does
main4 = return () >>= \ (!c) -> return ()


-- does
main5 = let !x = 1 in return ()


-- does
main6 = do
    ~c <- return ()
    return ()

-- does
main7 = return () >>= \ ~c -> return ()

-- dons

Trac metadata

Trac field	Value
Version	6.6
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler (Parser)
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system	Unknown
Architecture	Unknown