#2806: Require bang-patterns for unlifted bindings
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Reporter: simonpj | Owner:
Type: feature request | Status: new
Priority: normal | Milestone: 6.12 branch
Component: Compiler | Version: 6.8.3
Severity: normal | Keywords:
Difficulty: Unknown | Testcase:
Architecture: Unknown/Multiple | Os: Unknown/Multiple
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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
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2806>
GHC <http://www.haskell.org/ghc/>
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