On Sun, 2008-11-23 at 19:37 +0530, Vishal Belsare wrote:
Hi,
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.
Note: Hugs is using the wrong definition of sum, that's why it has different behaviour. 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': http://hackage.haskell.org/trac/haskell-prime/ticket/120 Duncan