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NNTP-Posting-Date: Thu, 08 Nov 2012 13:38:19 -0600
From: Chris Hinsley <chris.hinsley@gmail.com>
Newsgroups: comp.lang.forth
Date: Thu, 8 Nov 2012 19:38:19 +0000
Message-ID: <201211081938193500-chrishinsley@gmailcom>
References: <2012110713421835115-chrishinsley@gmailcom> <509bb9a2$0$6999$882e7ee2@usenet-news.net> <201211081406178276-chrishinsley@gmailcom> <509bf42e$0$11653$882e7ee2@usenet-news.net>
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Subject: Re: Genral advise and comments on callback style words
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On 2012-11-08 18:04:30 +0000, Josh Grams said:

> Chris Hinsley wrote: <201211081406178276-chrishinsley@gmailcom>
>> On 2012-11-08 13:54:42 +0000, Josh Grams said:
>>> Chris Hinsley wrote: <2012110713421835115-chrishinsley@gmailcom>
>>>> Folks I have implamented an Amiga style double linked list words set a
>>>> few days back and I have an emueration word as follows:
>>>> 
>>>> \ ( u xt lh -- ln | 0)
>>>> \ xt api is ( u ln lh -- ln | 0 )
>>>> : LISTHEAD-ENUMERATE-FORWARDS
>>>> 	0 >R
>>>> 	DUP LISTHEAD-GET-HEAD DUP
>>>> 	BEGIN
>>>> 		NIP DUP LISTNODE-GET-SUCC
>>>> 		DUP
>>>> 	WHILE
>>>> 		4 PICK 2 PICK 4 PICK
>>>> 		6 PICK EXECUTE DUP R!
>>>> 	UNTIL THEN
>>>> 	2DROP 2DROP DROP
>>>> 	R>
>>>> ;
>>> 
>>> And just out of curiosity, why are you calling GET-HEAD and then
>>> GET-SUCC before you do anything?  Doesn't that skip the first list node?
>> 
>> I'm keeping a 'look ahead' pointer to the next node in the list, as the
>> callback is allowed to trash the current node ! For instance it could
>> remove the node and then your left dangling !
> 
> Ah, I see.  I thought you were keeping the previous one and getting the
> successor of that after the XT returned.  Guess I didn't untangle the
> PICKs carefully enough.
> 
> Hrm...I still think it's wrong...unless LISTNODE-GET-SUCC does something
> really strange like ( node node -- node.next node ), then your WHILE is
> checking the successor to see if it's null, so you won't process the
> final element in the list...?  Or am I missing something again?
> 
> --Josh

In this forward enum case both HEAD and SUCC end up being just a ! 
because HEAD and SUCC are 0. But in the backwards enumeration TAIL and 
PRED are 8 and 4 respectivly.

Chris