Re: slight difference in strictness between -O0 and -O

On 3/12/07, Kirsten Chevalier wrote:

On 3/12/07, Kirsten Chevalier wrote:

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On 3/12/07, Albert Y. C. Lai wrote:

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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.

What version of ghc?

I was curious, so I checked this against ghc 6.6. Indeed, it exhibits the behavior Albert describes above. Same goes for the HEAD. In ghc 6.4.2, however, the program prints "x" whether compiled with -O or -O0.

This does seem like a bug to me.

I noticed that compiling with -O -frules-off causes the test program here to correctly print out "x". So, I was looking at the "take" rule in GHC/List.lhs. Doesn't this rule change the strictness of take? "take" [~1] forall n xs . take n xs = case n of I# n# -> build (\c nil -> foldr (takeFB c nil) (takeConst nil) xs n#) Cheers, Kirsten -- Kirsten Chevalier* chevalier@alum.wellesley.edu *Often in error, never in doubt "It's a woman's dream, this autonomy / Where the lines connect and the points stay free" -- Ferron