Require bang-patterns for unlifted bindings

GHC allows let/where bindings for unlifted values, but they are necessarily strict. That does lead to confusing behaviour. For example, 'f' and 'g' behave differently here:

    {-# LANGUAGE MagicHash #-}

    import GHC.Base
    import GHC.Exts

    main :: IO ()
    main = do print (I# (f 5# 0#))
              print (I# (g 4# 0#))

    f :: Int# -> Int# -> Int#
    f x y | False = x `divInt#` y
    f x y = x

    g :: Int# -> Int# -> Int#
    g x y | False = z
        where z = x `divInt#` y
    g x y = x

Suggestion: require that an unlifted let/where binding has a bang on it. That would make lifted and unlifted bindings behave uniformly.

Simon

Trac metadata

Trac field	Value
Version	6.8.3
Type	FeatureRequest
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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