[colorforth] ColorForth: if and -if

["Ray St. Marie" <ray.stmarie@xxxxxxxxx>]

---------- Forwarded message ----------
From: Ray St. Marie <ray.stmarie@xxxxxxxxx>
Date: May 20, 2007 4:23 AM
Subject: Re: ColorForth: if and -if
To: Josef <josefg@xxxxxxxxx>


On 5/16/07, Josef <josefg@xxxxxxxxx> wrote:
> Ray,
>
> I have tried using if and -if in colorforth, but there is something I am
> missing.
>
> I know if checks if the zero flag is set. How do I set the zero flag?
>
> I know -if checks the sign flag. How do I set the sign flag?
>
> Thank you,
>
> Josef
> --
> Using Opera's revolutionary e-mail client: http://www.opera.com/mail/

Hi Josef, I hope this finds you well.
Sorry for delay, I'm back online now. :)
This should help JC too, as I saw him with a similar question in the
FREENODE irc logs at #c4th.


IF and -IF in colorforth.

You are correct. If and -If test flags just as you say.
As you may or may not know, IF and -IF in colorforth are
"non-consuming" meaning that they don't consume stack arguments like
the ANS Forth versions.  This also means that they don't contain the
code that would set flags, so you have to do this first, and here's
how...

IF

If we wanted to test if a value is equal to another value, say 0 in
this case then use this....

... 0 or drop if if-true-code then ....

the OR tests the stack value with 0, consumes the 0 on the  test, sets
the 0 flag in the flags register and the IF tests that. The drop drops
the test value from the stack. You can omit the drop, or move it to
past the IF or past the THEN should you need to. This way you can
carry the stack value into the IF should you need to.

in the case of -IF

... 0 + drop -IF if-true-code then ....

In this case we are testing if the sign on the stack is neg or pos by
adding 0 to the stack value with the + word, which will set the sign
flag.

I've defined a couple macros based on these IF "prefixes", for want of
a better word. Such as...

: 0? 0 or drop ;  ( like 0= . All of those words are cyan [ with
exception of the last semi-colon which is green] as they are all
macros themselves.)

: ?exit ( like 0; in retroforth ) 0? if ; then ;  ( you can have two
semi-colons in a colorforth word. They too are all cyan words [as 0?
is now defined] with exception of the last semi-colon which is green.
)


While i'm here,

JC you may have answered this for yourself already but....
You wanted to know how to initialize a colorforth variable before
loading the block and setting the value. Try this....

newvar 0 10 newvar ! ( where "newvar 0" is the magenta/green variable
being defined and "10 newvar !" is all in yellow and somewhere after
the define.

Great to be alive and back in the world. Hope everyone is well!
BYE
Ray

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