id,summary,reporter,owner,description,type,status,priority,milestone,component,version,resolution,keywords,cc,os,architecture,failure,difficulty,testcase,blockedby,blocking,related
1219,RULE for take is too strict,simonpj,igloo,"{{{
main = print (map (const 'x') (take 1 (undefined:undefined)))
}}}
In ghci, or with ghc -O0, this produces `""x""`. With ghc -O, this produces `Prelude.undefined`.  Kirsten Chevalier found that the culprit is the RULE:
{{{
""take""     [~1] forall n xs . take n xs 
    = case n of I# n# -> build (\c nil -> foldr (takeFB c nil) 
                                                (takeConst nil) xs n#)
}}}
This rule makes `take` strict in `xs`, but it should be lazy when `n`=0.",merge,closed,normal,6.6.1,libraries/base,6.6,fixed,,,Unknown/Multiple,Unknown/Multiple,,Easy (less than 1 hour),,,,