[Haskell-cafe] stack overflow pain

Tim Docker tim at dockerz.net
Thu Sep 22 00:17:09 CEST 2011

I'm getting a stack overflow exception in code like this:

         -- applyAction :: A -> IO [B]

         vs <- fmap concat $ mapM applyAction sas
         return vs

I don't get it if I change the code to this:

         -- applyAction :: A -> IO [B]

         mapM_ applyAction sas
         return []

But of course, I need the results from the actions. I know that
the returned list contains approximately 1 million items.

Any suggestions on how I should rewrite the first code snippet
to not blow the stack?

I do find debugging stack overflow errors quite difficult - with little
information from the runtime I'm often left guessing which parts of
a large codebase might be causing them.

Note that there's plenty of heap space available, it's the evaluation
stack that is being used up. I could run with -K to increase the size
of the stack, but if possible I'd rather solve this in the code.

Thanks for any pointers.


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