Hi,
thanks for your investigation. I've only some basic knowledge about a narrowing
machine, so I don't understand the words 'thunk' and these. Is there a paper or
documentation available somewhere?
> If the definition of seq is inlined, then we get the (much better):
>
> case z of z' -> foldl' f z' xs
>
Did I understand the strictness of the case statement right:
case z of z' forces that z' (and z) will be in head normalform?
> I checked this with both ghc-3.02 and ghc-4.00 with and without -O,
> and except for ghc-4.00 without -O they all require a constant 200
> bytes or so of heap.
I got other results. With -O and ghc-3.02 (pl0) the program below (simplified
version of the 5-line example) needs linear heap space, without -O it needs
constant heap space (about 1KB).
So I'm confused!
That's my whole test program:
module Main where
import Numeric
-------------------------------------------------------------------------------
seq1 :: Int -> [Int]
seq1 x = x:seq1 x
-------------------------------------------------------------------------------
foldl' :: Eval a => (a -> b -> a) -> a -> [b] -> a
foldl' f a [] = a
foldl' f a (x:xs) = strict (foldl' f) (f a x) xs
numberOfOne :: Int -> Int
numberOfOne n = foldl' (\x y -> 0) 0 (take n (seq1 1))
-------------------------------------------------------------------------------
readNum :: Integral a => String -> a
readNum = fst . head . readDec
main = do
putStr "n = "
input <- getLine
n <- return (readNum input)
output <- return (numberOfOne n)
putStrLn (show output)
