[Haskell-cafe] Haskell maximum stack depth

Neil Mitchell ndmitchell at gmail.com
Mon Jan 28 13:07:01 EST 2008


> ghc uses a pretty conventional stack AFAIK, and it is arbitrarily
> limited, but you can change the limit with +RTS options.

GHC uses a conventional stack (in that you put stuff at the top, and
take it off from the top), but it is not a conventional stack in the
way imperative programs work. In an imperative program if you make a
function call, a frame gets pushed on the stack. When the function
call returns, the frame gets popped off the stack. In Haskell, lazy
evaluation makes it massively more confusing.

> Also, stack "overflows" are a pretty common cause of program failure
> IME, not at all rare. At least, far more common than whatever error
> message you get from heap exhaustion (can't even remember the last
> time I saw one of those).

Yes, I agree. However, in imperative programming stack overflow nearly
always means you've exceeded some recursion depth in the program, and
should think about refactoring it to use explicit loops. In Haskell,
stack overflow is usually a laziness bug. Same error message,
completely different causes. In Haskell, the solution to stack
overflow is almost never "increase the stack depth", but "fix your
laziness leak".

To answer the question if Haskell has a "stack depth restriction ...
like Java" the answer is no. It has a stack depth restriction, but its
absolutely nothing like Java in the way it uses the stack, so you
can't compare them.

My guess is that Istarex's inner thought might have been along the
lines of "in Java if I do too much recursion I get a stack overflow,
but Haskell only has recursion, does that mean I get into stack
overflows all the time?". I could of course be entirely wrong ;-)



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