With expl3, I can \peek_charcode:NTF. For debugging, I would like to actually see the peeked-ahead tokens for each iteration of my loop, but have not seen a suitable token variable in the documentation.
1 Answer
The documentation about \peek_after:Nw tells that the looked at token is available in \l_peek_token and this is how work all the following functions (which are based on \futurelet).
Probably the documentation should make this clearer.
Here's an example:
\documentclass{article}
\usepackage{expl3}
\ExplSyntaxOn
\peek_charcode_remove:NTF
B
{ \tl_show:N \l_peek_token }
{ \tl_show:N \l_peek_token \tl_show:N }
A
\peek_charcode_remove:NTF
B
{ \tl_show:N \l_peek_token }
{ \tl_show:N \l_peek_token \tl_show:N }
B
\ExplSyntaxOff
\stop
Here's the relevant part of the log file:
This is pdfTeX, Version 3.1415926-2.5-1.40.14 (TeX Live 2013) (format=pdflatex 2013.11.14) 14 NOV 2013 21:50
entering extended mode
restricted \write18 enabled.
%&-line parsing enabled.
**peek.tex
(./peek.tex
LaTeX2e <2011/06/27>
[...]
> \l_peek_token=the letter A.
<recently read> }
l.8 A
?
> A=the letter A.
<recently read> }
l.8 A
?
> \l_peek_token=the letter B.
<recently read> }
l.14 B
?
)
Here is how much of TeX's memory you used:
5223 strings out of 493308
95482 string characters out of 6137815
131918 words of memory out of 5000000
8695 multiletter control sequences out of 15000+600000
3640 words of font info for 14 fonts, out of 8000000 for 9000
957 hyphenation exceptions out of 8191
31i,1n,33p,203b,85s stack positions out of 5000i,500n,10000p,200000b,80000s
No pages of output.
PDF statistics:
0 PDF objects out of 1000 (max. 8388607)
0 named destinations out of 1000 (max. 500000)
1 words of extra memory for PDF output out of 10000 (max. 10000000)
Since I used \peek_charcode_remove:NTF only the meaning of A appears twice.
\l_peek_token