sum[1..100000] --> stack overflow in GHC, but not in Hugs?
duncan.coutts at worc.ox.ac.uk
Sun Nov 23 10:22:06 EST 2008
On Sun, 2008-11-23 at 19:37 +0530, Vishal Belsare wrote:
> Please bear with a very basic question. I am trying to 'learn me a
> Haskell for great good' using Hutton's book and some online tutorials.
> I started off with Hugs and recently used GHC (to use the 'let a =
> .." syntax interactively, which Hugs doesn't allow perhaps).
> There's a simple issue I am having with GHC. sum[1..100000] works fine
> on Hugs, however, the same in GHCi generates a stack overflow
> exception. I am trying to figure out what's going on.
Hugs is using the wrong definition of sum, that's why it has different
The Haskell98 report defines them as:
sum, product :: (Num a) => [a] -> a
sum = foldl (+) 0
product = foldl (*) 1
While hugs uses:
sum, product :: Num a => [a] -> a
sum = foldl' (+) 0
product = foldl' (*) 1
Obviously these have different semantics (eg on lazy Num instances) as
well as different operational behaviour. Either hugs or the Prelude
should be fixed.
It is a bit odd that they're defined with foldl, since if they were
really meant to be lazy then why were they not defined with foldr?
It is being considered for Haskell':
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