On Thu, Dec 14, 2006 at 04:00:53PM +0100, Felix Breuer wrote:
Hello everyone,
I have been trying to run a Haskell program of mine that does an extensive computation with very large amounts of data. I compiled the program with ghc --make. When I run it it terminates after some time with the message:
Stack space overflow: current size 8388608 bytes. Use `+RTS -Ksize' to increase it.
The program isn't that well written so the overflow did not surprise me, I expected that it might run out of memory. What did surprise me was the *stack* overflow. I do not use recursion in my program except for a couple of fold operations over very large lists. So I have a number of questions:
1) Which Haskell operations cost space on the stack, which cost space on the heap? I guess this is implementation dependent, so I looked into the GHC manual but did not find an answer. Where can I look these things up?
Lazily evaluated functions seem to get stuck on the stack., so space on the stack tends to get used up by over-lazy programs, which take a long time before they actually evaluate anything. But I'm not quite clear myself when exactly things go on the heap or the stack.
2) What could be possible sources of a stack overflow? (Apart from a recursive but not tail-recursive function.)
It's probably your folds. I can never keep them straight, but quite likely switching to a stricter variant will help you, which are named with a "'" at the end, e.g. foldl'. If you post your program here, I'd guess someone will take a look at it and give you a better suggestion where the trouble is. It can be hard to track down, I'm afraid.
3) I tried using +RTS -K<size> as suggested, but these options do not seem to be passed through if I use --make. How can I use both, these compilation flags and --make?
You pass +RTS -K<size> to your executable, not when compiling (which would affect the stack of ghc). :) -- David Roundy Department of Physics Oregon State University