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: Thu, 27 Oct 2016 19:13:45 -0400
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On Mon, 24 Oct 2016 20:42:59 -0700 (PDT)
trans <transfire@gmail.com> wrote:

> A paper called Stack Quarks by Rob Chapman[2] gives one way to look
> at it, though it is very hardware oriented. He gives six elemental
> operations which can be combined to make the operations we use in
> Forth. For example, a DROP is DIP NIP, and DUP is a NUP DRIP. But I
> don't see how he accounts for, say, swapping the NOS and the top of
> the remaining stack (the third item).

: NIP SWAP DROP ;
: TUCK SWAP OVER ;
: NUP OVER SWAP ;
: DIP DROP DUP ;
: TAKE DROP SWAP ;
: DRIP SWAP DIP ;

> Of course, what are the fundamental stack operations? 
> [...]
> In any case, the operations from a coder's perspective are probably
> the more pertinent operations for a symbolic notation, the
> fundamental operations seem to me to be:
> 
>     drop
>     dup
>     swap
>     push (>r)
>     pull (r>)
> 
> With these five I think all others are possible. Do you agree?

Generally, you need DUP DROP SWAP >R R> to create the other
single-cell stack operators, efficiently.  Likewise, it's more efficient
for double-cell operators if you have 2DUP DROP 2SWAP 2>R 2R> available.
However, all the double-cell operators can be created using single-cell
operators DUP DROP SWAP >R R> .  Unfortunately, the length of some these
double-cell definitions can become very long, e.g., 18 to 22, when
using single-cell operations.

Alternately, you can use PICK ROLL -ROLL SWAP DROP.  Note that PICK
ROLL -ROLL take a size argument.


Rod Pemberton