Path: csiph.com!aioe.org!.POSTED!not-for-mail
From: Rod Pemberton <NeedNotReplyHere@xrsevnneqk.cem>
Newsgroups: comp.lang.forth
Subject: Re: Stack Operator Symbols
Date: Sat, 29 Oct 2016 18:46:35 -0400
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On Sat, 29 Oct 2016 00:46:20 -0700
Paul Rubin <no.email@nospam.invalid> wrote:

> "Elizabeth D. Rather" <erather@forth.com> writes:

> > I wrote Forth professionally for 30 years without using PICK, ROLL,
> > or -ROLL, suffering zero inconvenience.  
> 
> I needed a 3DUP word recently, and wrote something like:
> 
>    : 3dup ( a b c -- a b c a b c ) >r 2dup r@ -rot r> ;
> 
> Later I saw someone else's implementation:
> 
>    : 3dup ( a b c -- a b c a b c ) 2 pick 2 pick 2 pick ;
> 
> which I thought was much more symmetric and natural.  Of course for
> non-purists,
> 
>    : 3dup { a b c } a b c a b c ;
> 
> is the simplest of all.

Alex McDonald has a solver based on code from Anton Ertl, IIRC.  I
also have another based on Java code by Peter Sovietov.

So, there are many ways to implement 3DUP depending on what Forth words
you want to use.  Here are a few:

: 3DUP DUP >R SWAP DUP >R SWAP >R >R DUP R> SWAP R> SWAP R> R> ;
: 3DUP OVER >R >R OVER R> SWAP OVER R> SWAP ;
: 3DUP >R OVER OVER R@ -ROT R> ;
: 3DUP >R NUP TUCK R@ -ROT R> ;
: 3DUP >R 2DUP R@ -ROT R> ;
: 3DUP >R R@ R> 2OVER ROT ;
: 3DUP DUP 2SWAP 2TUCK ROT ;
: 3DUP DUP 2OVER ROT ;


Rod Pemberton