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Subject: Re: bugs, Bugs and BUGS!

Author: James Swafford

Date: 15:27:53 05/29/04

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On May 29, 2004 at 17:47:02, Sune Fischer wrote:

>On May 29, 2004 at 11:33:01, James Swafford wrote:
>>>
>>>How would you pass arguments to a function in an unevaluated state? Can you draw
>>>a stack frame showing exactly what would be done?
>>
>>The problem (well, Uri's problem) is the order in which the compiler
>>evaluates the expression tree.  Think of 'printf' as a node in a tree
>>with the parameters as children.
>>
>>Apparently the children are evaluated first (bottom up), and since
>>they share memory, voila...
>>
>>I think printf could do something like:
>>
>>While (unevaluated parameter) {
>>   evaluate parameter
>>   copy results to buffer
>>}
>>print buffer
>>
>>Not as efficient, but it would work.
>>
>>Note I am _not_ saying it _should_ work this way!
>
>From what I understand the problem is not with printf, but in the way parameters
>are passed to functions in general.
>
>Eg. if I write F(3*x+4,0.6*y-2), then the program will first evaluate the
>argumens and _then_ pass them to the function, F.
>
>It is not possible for the compiler to replace that with two calls like F(3*x+4)
>and F(0.6*y-2), because the compiler can't possibly know if F can handle that.
>
>Printf is no exception I think, it gets treated like any other function in this
>respect.

No... perhaps C can't do this because of the way the language is
defined, but you _can_ change the order in which expressions are
evaluated.  Functional languages are good examples of how a
parameter might not get evaluated at all.

Languages that do this use what's called 'lazy evaluation', or
'outside-in evaluation'.

--
James



>
>-S.
>>--
>>James



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