Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!SUN.COM!wmb
From: wmb@SUN.COM (Mitch Bradley)
Newsgroups: comp.lang.forth
Subject: Re:  ANS FORTH/PICK and ROLL
Message-ID: <8911152104.AA10027@jade.berkeley.edu>
Date: 15 Nov 89 19:24:11 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Reply-To: Forth Interest Group International List <FIGI-L%SCFVM.bitnet@jade.berkeley.edu>
Organization: The Internet
Lines: 58

> How WOULD you get along without [PICK and ROLL]

I get along without ROLL just fine.  I can't remember the last time
I used it.  The only thing I would miss is "2 PICK".

Like the article in Forth Dimensions says, you can always implement
PICK and ROLL in high level if you have to.

You need not worry, because most vendors are going to implement the
full core extension wordset anyway, for marketing reasons.

The "required/extension" separation is really a political technique
used to facilitate compromise between standards team members.
For some words, there is a "must have it" camp and a "no way, I don't
want to burden my system with that useless word" camp.
Such words often end up in the extension part of a wordset.

The need for PICK is somewhat reduced by the existence of local variables.
At the last meeting, a proposal for local variables was adopted.  Here is
how it works:

LOCAL name   ( initial-value -- )

 Used inside a colon definition to define a local variable.
 When the colon definition is executed, the stack is popped into
 the local variable.  When name is later used within that
 definition, the value is left on the stack.

TO name   ( value -- )

 Changes the value of a local variable.


Here's an example.  This word looks for the first occurrence of the
value "test" between start-addr and start-addr + size .  It illustrates
the use of LOCAL/TO and multiple WHILEs .  I have used capitalization
to point out new usage.

: search  ( test start-addr size -- test next-addr size found-addr found? )
   swap   LOCAL addr           ( test size )
   addr + LOCAL end-addr       ( test )
   LOCAL test

   BEGIN
      addr end-addr <
   WHILE
      addr @  test -
   WHILE
      addr  1 cells +  TO addr
   AGAIN THEN THEN  \ resolve both "while"s
                                \ REPEAT THEN  would have worked too

   addr end-addr <  if
      test   addr 1 cells +   end-addr addr -   addr  -1
   else
      test   end-addr         0                 0     0
   then
;