[ColorForth] Equality

[Bob Shafer <bobsh@xxxxxxxxx>]

Oops. Of course I meant:

: things
  5 ? if 5thing ; then
  11 ? if 11thing ; then
  38 ? if 38thing ; then
  otherthing ;


On Thu, 20 Jun 2002, Bob Shafer wrote:

> If you are comparing against a literal (as it appears you are), then you
> can use the "?" macro:
> 
>    "n ?" will compile "TEST EAX, n"
> 
> : things
>   5 eq if 5thing ; then
>   11 eq if 11thing ; then
>   38 eq if 38thing ; then
>   otherthing ;
> 
> Notice that if the stack has one item on it going into "things", then
> it'll still have that one same item on it going into "5thing" and etc.
> 
> Unless I'm completely misunderstanding all this, that is. :-)
> 
> On Thu, 20 Jun 2002, Richard Collins wrote:
> 
> > I feel like an idiot asking this. But here goes anyway.
> > 
> > How does one get by without an equals operator. I want to say something like
> > this:
> > 
> > 5 5 eq if 5thing then ;
> > 
> > I could rearrange it to:
> > 
> > 5 5 xor if ; then 5thing ;
> > 
> > But this seems like too much of a fudge, particularily because what I really
> > want to do is more like,
> > 
> > : things
> > dup 5 eq if 5thing ; then
> > dup 11 eq if 11thing ; then
> > dup 38 eq if 38 thing ; then
> > drop otherthing ;
> > 
> > which becomes
> > 
> > : things
> > dup 5 xor if
> >     dup 11 xor if
> >         dup 38 xor if drop otherthing  ; then 38thing ;
> >     then 11thing ;
> > then 5thing ;
> > 
> > Defining eq as
> > : eq xor - drop ;
> > doesn't work as - doesn't affect the pentiums flags.
> > 
> > My last resort is to define a new 'if', 'if0' which jumps forward to the
> > next 'then' when the zero flag is not set, instead of when it is set, which
> > is how 'if' works. This would not be hard, but I can't help but think that
> > if it was needed, Chuck would have put it there.
> > 
> > I'll be grateful for any advice. I suspect I am approaching things from the
> > wrong angle.
> > 
> > Thanks, Richard Collins
> > ------------------------
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