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Posting-Front-End: Gnews 1.1


In article <5673@watdragon.waterloo.edu> you write:
>This is just not true.  For ordinary procedure calls, a global
>display involves trivial entry and exit overhead.  The only time
>displays get expensive is if you do lots of "functional" style 
>programming - passing procedures as parameters and/or using
>procedure variables.

Carefull. If you have full procedure variables, you even cannot
use the usual stack of activation records, because the extent of
a procedure doesn't end necessarily, when you leave it.

>Even this is quite bearable - it uses time
>and space proportional to n to build a local copy of the display
>in order to pass a procedure (or procedures) as a parameter.

And you have to pass variable length, big objects around.

>Here is a comparison of the time to do static links vs. displays.
>(in terms of "n", the level of nesting).
>
>    STRATEGY:        static links          global disply
>
>    ENTRY CODE:        O(1)                    O(1)
>    EXIT CODE:         0                       O(1)
>    NONLOCAL REF:      O(n)                    O(1)
>    FUNC PARM:         O(1)                    O(n)*

Yes, and now? If you realize, that NONLOCAL REF account for less
than ONE PERCENT of all references (if we consider LOCAL-1 to be
nearly LOCAL, cf. <4808@sigi.Colorado.EDU>), why should one use
displays?? 

	Michael Schmidt