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[Help] How to deal with StackOverflowException
f#

I'm just starting to learn F# via Expert F#.

Refering to the factorial function in p40 in the book, I've rewritten it as follows:

let rec factorial(n) =

try

match n with

| _ when n >= 1 -> 1

| _ -> n * factorial(n-1)

with :? StackOverflowException -> 0

printfn "%d" (factorial(10000000))

I expected the result would be 0.

But the result is fsi's terminated.

MSDN doc says :

Starting with the .NET Framework version 2.0, a StackOverflowException object cannot be caught by a try-catch block and the corresponding process is terminated by default.

Please tell me how I can handle this problem in this specific factorial problem.

Thanks in advance.

.

Hi, The solution for your problem is to fix the spelling error. :)
Just replace >= 1 with <= 1 and it will work. By definition, factorial(0) is 1.

You can also handle the < 0 case and raise an exception.

Laurent

By on 11/5/2008 11:30 AM ()

| _ when n >= 1 -> 1

Actually, this should return 1 and not involve a stack at all.

By on 11/5/2008 11:03 AM ()

Hi,
I'm afraid there is really no way to catch this exception.
The solution for this specific problem is to use "tail-recursion" - this means that you can rewrite the code in a way that it is still recursive, but it doesn't take any space on the stack. This is discussed in Expert F# in chapter 8 around page 199, so you may want to check this part of the book.

T.

By on 11/5/2008 3:09 AM ()

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