# using less stack

**C.Reinke
**
C.Reinke@ukc.ac.uk

*Wed, 20 Mar 2002 18:12:12 +0000*

>* > > cpsfold f a [] ú
*>* > > cpsfold f a (x:xs) ÿ x a (\y -> cpsfold f y xs)
*>* >
*>* > and f takes a continuation, Bob's my uncle, and I have a program that
*>* > runs quickly in constant space!
*>*
*>* Good. I'm curious to know from other readers whether
*>* continuations like this are the only way of solving it,
*>* though.
*
Actually, and quite apart from it being cumbersome to use, I've got
my doubts about whether this cpsfold really does the job (is that
just me missing some point?-).
Also, I'm curious to know why the usual strict variant of foldl
doesn't help in this case?
foldl' f a [] = a
foldl' f a (x:xs) = (foldl' f $! f a x) xs
or, with the recently suggested idiom for strictness, tracing and
other annotations:-)
annotation = undefined
strict a = seq a False
foldl' f a l | strict a = annotation
foldl' f a [] = a
foldl' f a (x:xs) = foldl' f (f a x) xs
Claus