"Ch. A. Herrmann" wrote:
Hi Haskellers,
which compiler settings do I have to pass to ghc-5.02 in order to achieve that the strictness analyzer recognizes strictness of (+) in foldl and computes sum in constant space?
Prelude> sum [1..10000000]
had the following effect:
PID USER PRI NI SIZE RSS SHARE STAT %CPU %MEM TIME COMMAND 23542 herrmann 20 0 250M 130M 97500 R 66.3 52.4 0:21 ghc-5.02
Of course, one could define a strict foldl oneself:
sfoldl f e [] = e sfoldl f e (x:xs) = (sfoldl f $! (f e x)) xs
There is a foldl' in the Hugs Prelude that does this: foldl' :: (a -> b -> a) -> a -> [b] -> a foldl' f a [] = a foldl' f a (x:xs) = (foldl' f $! f a x) xs There are some functions in the Hugs Prelude that use foldl (or foldl1) and some use foldl'. Maybe someone can explain why certain functions use foldl: reverse, maximum, minimum and readInt, while others use foldl': length, sum and product. I can understand why reverse would use foldl, but why do maximum, minimum and readInt use foldl ? Maybe the function foldl1 was based on foldl' at one time ? Jan