Re: Locals revisited

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 ! ;

\ Misc examples
: (H.)  ( u -- adr len )  [ 2 cells ] literal (h.n) ;
: (HW.) ( u -- adr len )  4 (h.n) ;
: (HB.) ( u -- adr len )  2 (h.n) ;

: (HD.) ( ud -- adr len )
  (h.) holds  (h.)  [ -2 cells ] literal /string ;

: .HB ( u -- )  2 (h.n)  [char] $ hold  #> type space ;

: h.n ( u n -- )  (h.n) type ;

: DUMP ( addr u -- )  \ Dump u bytes in hex and ascii
  cr  3 spaces  16 0 do  over i +  2 spaces  1 h.n  loop
  bounds ?do
    cr  50 ms  halt? if unloop then
    i 4 h.n space
    16 0  do  i j + c@  2 h.n space  loop
    16 0  do  i j + c@  dup 127 bl within
      if  drop  [char] .  then  emit
    loop
  16 +loop ;