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< Erlang ~ Recursive function calls and stack |
| lucasm |
 Posted: Sun Apr 19, 2009 11:11 pm |
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Joined: 19 Apr 2009
Posts: 1
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Hello.
When a function recursively calls itself, are all the parameters copied on to the stack? The reason I am asking: I recently wrote a program that was passing very long lists of integers (16000 +) to a function. The function would call itself recursively and pass along the very long list as a parameter. This particular implementation proved to be rather slow, and I am suspecting the culprit was that the very long list list was copied on the stack each time a function was called, resultint in a lot of memory traffic and usage. Is my understanding correct?
Thanks in advance, Lucas |
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| uwiger |
| Posted: Mon Apr 20, 2009 1:33 pm |
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Joined: 03 Jul 2006
Posts: 604
Location: Sweden
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lucasm wrote: Hello.
When a function recursively calls itself, are all the parameters copied on to the stack?
No. The list is created once and only referred to (with a pointer) on the stack. If the argument is passed along unchanged to the next function/iteration, the cost will be the same whether the argument is a huge list or a simple atom.
BR,
Ulf W |
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| seancribbs |
| Posted: Sun May 03, 2009 5:41 pm |
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Joined: 03 May 2009
Posts: 17
Location: Chapel Hill, NC
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lucasm wrote: The reason I am asking: I recently wrote a program that was passing very long lists of integers (16000 +) to a function. The function would call itself recursively and pass along the very long list as a parameter. This particular implementation proved to be rather slow, and I am suspecting the culprit was that the very long list list was copied on the stack each time a function was called, resultint in a lot of memory traffic and usage.
This would only be the case if your recursive call is not the last thing in the function. Erlang is able to do TCO (tail-call optimization), which essentially amounts to a GOTO or JMP after the optimization. Try to refactor your function to call itself last. And what Ulf said. |
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