Re: [Amforth-devel] words: tuck/under etc

[Ulrich H. <uh...@xl...>]

Hi Mike,

> Hm, what makes the differencce in using
> : perform   postpone @ postpone execute ; ( A )
> instead of
> : perform  @ execute ; ( B )
> then? Speed?


it has to be either

: perform ( compiling: -- ) ( interpreting:  xt -- )
      postpone @  postpone execute ;
immediate

or just

: perform ( xt -- )  @ execute ;

The latter is the typical definition.

The first definition compiles code so in principle
could be removed from the final program. This however
is seldomly done as only few Forth systems support
temporary definitions.

Speedwise the first version might be slightly faster as
less nesting is done. However the effect is probably
marginal and not worth the effort....

I personally would define PERFOM only for
porting code. I believe

@ EXECUTE

makes a fine phrase to be writen in source.
If I build data/control structures it will be hidden in
that definition anyway, like:

: Case:  ( -- )  Create Does>  ( i*x -- j*x ) cells + @ execute ;

Case: choice   ' dup ,  ' swap , ' drop ,

10   0 choice ( dup )
20   1 choise ( swap )
2 choice ( drop )   2 choice ( drop )   2 choice  ( drop )


F83 has PERFORM implemented in code which might
have the speed advantage.... Benchmarking required.

Regards,
			Ulli


Am 16.07.2008 um 10:37 schrieb Kalus Michael:

> Hi Ulli.
>
> Am 16.07.2008 um 08:12 schrieb Ulrich Hoffmann:
>>> Is the solution now to use *: perform postpone @ postpone execute;
>>> *??
>> yes
>
> Hm, what makes the differencce in using
> : perform   postpone @ postpone execute ; ( A )
> instead of
> : perform  @ execute ; ( B )
> then? Speed?
>
> Looks like Version A acts like an makro compiling @ and EXECUTE into
> your definition, so that at runtime there will be less overhead
> because we skip one NEXT level this way? If speed does not matter
> that much version B will do the same thing?
>
> Michael
>
>
>
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