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Mailing list for the LaTeX3 project <[log in to unmask]>
Mon, 6 Feb 2012 12:45:41 +0000
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* Bruno Le Floch <[log in to unmask]> [2012-02-06 06:36:23 -0500]:

Hi Bruno,

: The problem is that you \tl_use:N \l_expr_tl before defining \f:n. If
: you look at which line the error occurs, this is the line. To display
: a token list to the terminal (or log file), use one of the lines
: \tl_show:N \l_expr_tl
: \iow_term:x { \tl_to_str:N \l_expr_tl }
: \iow_log:x { \tl_to_str:N \l_expr_tl }
: Those differ in the details, but give you the information without
: expanding the token list: the last two lines convert the token list to
: a string of characters before printing them to the terminal or the log
: file. On the other hand, \tl_use:N is like typing the token list in
: your file. It will then be run as normal code, in particular expanding
: macros, including \f:n which is not defined yet.
: > In my recurrence equation implementation, defining \f:n _after_ the
: > substitution is possible, but it requires a bit more work. Does \f:n
: > have to be known at substitution time?
: It does not have to be defined at substitution time, but at use time.
: See below.

Thanks. I think I solved this problem. An level of expansion had
to be prevented. The substitution went fine, but when the regular
expression was inserted in the body of a macro definition the
resulting \f:n was evaluated:-) Adding a \c{exp_not:N} before the
\c{\u{l_recurrence_name_tl}:n}} dif the trick.

I'm still working on the other problems. Also I have to properly
read your last comments, but this will have to wait until after
my 2 p.m. lecture.

Thanks again for your help.