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From: dxf <dxforth@gmail.com>
Newsgroups: comp.lang.forth
Subject: Re: Locals revisited
Date: Mon, 31 Mar 2025 01:22:02 +1100
Organization: i2pn2 (i2pn.org)
Message-ID: <a1144a7ebbf33f269eaa3fd2d2322db8dca32cc0@i2pn2.org>
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On 30/03/2025 11:01 pm, albert@spenarnc.xs4all.nl wrote:
> In article <4b84665e38d5a523efc2479f48338ed55d142185@i2pn2.org>,
> dxf  <dxforth@gmail.com> wrote:
>> On 28/03/2025 8:38 pm, albert@spenarnc.xs4all.nl wrote:
>>> In article <19029ff0c8e7cf53335fe62639308e7f92d10240@i2pn2.org>,
>>> dxf  <dxforth@gmail.com> wrote:
>>>> On 27/03/2025 11:02 pm, albert@spenarnc.xs4all.nl wrote:
>>>>> In article <87semzmwok.fsf@nightsong.com>,
>>>>> Paul Rubin  <no.email@nospam.invalid> wrote:
>>>>>> albert@spenarnc.xs4all.nl writes:
>>>>>>> In hindsight my locals definition is not convincing, because carnal
>>>>>>> knowledge about the behaviour of the return stack is required.
>>>>>>
>>>>>> It's ok if it's for a specific implementation.  But what I'm having
>>>>>> trouble seeing is how the locals get popped in case of an exception.
>>>>>
>>>>>
>>>>> I showed it as an example of the pretty convincing usefulness
>>>>> of CO. For this the example had to have to be portable.
>>>>>
>>>>> A simpler example would be
>>>>> \ Temporary set  some-rounding-mode  for the duration of this word.
>>>>> : rounding set-rounding-mode CO truncate-mode set-rounding-mode ;
>>>>> ...
>>>>
>>>> Actually it was that example which caused me to *not* go ahead
>>>> and implement ;: in the kernel despite a cost of only one header.
>>>> How many calls to 'rounding' will you encounter in an application?
>>>
>>> `rounding: is an internal word in the fp package and it is used 4
>>> times.
>>>
>>>> My guess is one.  The usual example is HEX: but I already had (H.N)
>>>> that's more flexible.  For me at least locals was more credible but
>>>> again it fell into a range.  For a single use I'd do it manually;
>>>> for extensive use (where exceptions etc are likely) a proper locals
>>>> may be the only option.  OTOH such decision-making is exactly what
>>>> Forth has always been about.
>>>>
>>>>
>>>
>>> You can't argue with
>>>     :NONAME ." Before " .S CO ." After " .S ;
>>>     ' proc_contains_Heisenbug decorated
>>>
>>> Study python for the concept of decoration.
>>> This alone makes CO a worthwhile addition.
>>>
>>> I have (D.H) that uses CO. Undoubtedly your (H.N) is more complicated.
>>
>> Possibly though much of the complication lies in what it needs to do - as
>> opposed to radix save/restore.
>>
>> \ Convert unsigned number u to a hexadecimal string c-addr2 u2 in the
>> \ HOLD buffer beginning with the least-significant digits.  Exactly
>> \ +n hexadecimal characters are returned with any unused positions
>> \ being filled with character '0'.  BASE is preserved.
>> : (H.N) ( u +n -- c-addr2 u2 )
>>  base @ >r hex <# 0 tuck ?do # loop #> r> base ! ;
> 
> Same idea.
> ( Generate string with hex format of DOUBLE of LEN digits)
>  : 4?  1+ 4 MOD 0= IF &, HOLD THEN ;
>  : (DH.) HEX: <# 1- 0 ?DO # I 4? LOOP # #> ;
> 
> ( Derive B. H. DH. from them)
> 
> Only HEX: DEC: is made a separate facility:
> : HEX:    R> BASE @ >R  >R HEX CO R> BASE ! ;
> : DEC:    R> BASE @ >R  >R DECIMAL CO R> BASE ! ;
> To live on and fight another day, e.g. in formatting, or in at-xy that
> outputs a position in decimal.

The question then is can HEX: DEC: be justified.  While you might because
CO exists, I'm not sure I could.