🚀 go-pugleaf

>>>>> In article <726603701.528921.BNB@MATH.AMS.ORG>, BNB@MATH.AMS.ORG (bbeeton) writes:

bbeeton> julio dix (jd01@swtexas.bitnet, to comp.text.tex, jan 8) wants
bbeeton> to strip off the first digit from a series of digits in a box,
bbeeton> replacing the remaining digits into the same box.

bbeeton> i won't tackle the boxing part of the question, but can explain
bbeeton> why the whole string of numbers is being gobbled at once.

bbeeton> take a simpler example:
bbeeton> \newcount\num
bbeeton> \def\newnum#1#2.{\num=#1 \def\rest{#2}}
bbeeton> \newnum12345.
bbeeton> this will end up with \num=12345 and \rest empty (with a delimited
bbeeton> string, the part between delimiters need not contain anything).

Nope:

*\showthe\num
> 1.
<*> \showthe\num
? 
*\show\rest
> \rest=macro:
->2345.
<*> \show\rest

The relevant mechanism deciding this is not number parsing, but macro
parameter parsing.  I haven't seen the original post so can only guess
at the question asked, but perhaps the example

\newcount\num \def\digits{12345} \def\newnum#1#2.{\num=#1 \def\rest{#2}}
\newnum\digits67890.      %% Result: \num=12345 and \rest -> 67890
\expandafter\digits67890. %% Result: \num=1 and \rest -> 234567890

hits closer to the mark?

- Harald