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NNTP-Posting-Date: Thu, 08 Nov 2012 07:14:15 -0600
From: Chris Hinsley <chris.hinsley@gmail.com>
Newsgroups: comp.lang.forth
Date: Thu, 8 Nov 2012 13:14:15 +0000
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Xref: csiph.com comp.lang.forth:17149

On 2012-11-07 21:04:20 +0000, humptydumpty said:
> Building backward from EXECUTE and applying desired stack-effects,
> I've got:
> 
> : HEAD ( lh -- ln )   ;
> : SUCC ( ln -- ln' )  ;
> 
> 
> \ xt ( u ln lh--R|0 )
> : ENUMERATE     ( u xt lh -- R|0 )
> ( u xt lh )             swap >R
> ( u lh )                dup HEAD
> ( u lh ln )
>                         BEGIN
> ( u lh ln   )                   dup SUCC dup 0=
> ( u lh ln   ln' f )             IF  RDROP 2drop 2drop 0 EXIT THEN
> ( u lh ln   ln' )               swap 2over
> ( u lh ln'  ln u lh )           rot swap R@
> ( u lh ln'  u ln lh xt )        EXECUTE dup
> ( u lh ln'  R f=R )             IF  RDROP   nip nip nip EXIT THEN
> ( u lh ln'  R )                 drop
> ( u lh ln'  )           AGAIN
> ;

?DUP after the EXECUTE ? Then avoid the drop after the THEN ? But then 
your looking at a taken branch to an abolute jump !

> ( u lh ln'  u ln lh xt )        EXECUTE ?dup
> ( u lh ln'  R f=R )             IF  RDROP   nip nip nip EXIT THEN
> ( u lh ln'  )           AGAIN
> ;

Chris