length[1 .. n] seems to run in constant space (that is, space
independent of n), as expected.
However, length[1 ..] runs out of space.
This doesn't seem reasonable to me.
The following program, which computes length[1 ..]
and reports its progress after every n-th element, also runs out of
space, inexplicably to me.
> lens n = everyNth n . scanl (\n _ -> n+1) 0
> everyNth n = map head . takeWhile(not.null) . iterate(drop n)
> main = interact(("Enter stride: "++). unwords . map show .
> (flip lens)[1 ..] .
> fst . head . readDec)
With a stride of 1000, the program runs out of space
after 28,000 list elements with the default heap size in Hugs
on my Unix (Sun) installation, and after 164,000 list elements under ghc.
With larger strides, it runs out of space sooner on both Hugs and ghc.
What's going on here? It appears to me that both length[1..] and the
above definition of main should evaluate in constant space.
Rex Page
[EMAIL PROTECTED]
School of Computer Science 405-325-4397
University of Oklahoma fax 405-325-4044
Norman OK 73019-0631
