Dan Weston wrote:
> foldl (+) 0 [1..10000000] :: Integer
> *** Exception: stack overflow
> foldl' (+) 0 [1..10000000] :: Integer
> 50000005000000
I thought both of these were perfectly well defined in denotational
semantics (and equal to 50000005000000). The first is merely a failure
of one person's computer to implement the (perfectly well-defined)
denotational semantics of the program.
Quite. It's slightly confusing that a stack overflow manifests in the
same way as an exception that indicates _|_, such as error or divide by
zero.
It's exactly the same as if you'd pressed Control-C during the first
evaluation. That doesn't cause the expression to have value _|_, but it
does raise an exception. The type of the exception is some help:
StackOverflow is a constructor in the AsyncException datatype,
indicating that it was an asynchronous exception. Evaluating the
expression again might yield a result.
Cheers,
Simon
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