My situation is similar to, but hopefully different from How do I ‘expand’ a control sequence \let to a character?, as that question does not admit a positive answer. I want to parse, not expand, but not character by character, if I can avoid that (as in Parsing a macro argument character-by-character for conditional execution). Existing parsers like Can one define an expandable command that removes control sequences from its argument? seem not not work for me, unfortunately (well, I can't get them to work, that is).

Consider the following: There is this \let definition

\show\inthewayfalse % ->\let \ifintheway \iffalse .

that sits in a macro \parseme of which I want to extract the text 17

\def\parseme{\inthewayfalse 17}

How can I do that?

Obviously, expanding the macro with \edef\parsedmacro{\parseme} does not work and I get the complaint

! Incomplete \iffalse; all text was ignored after line 5.

However, adding a \fi in the \edef does not help, either. Is there something else I can do?

In my situation I even know what the obstacle is. It is always \intheway. Then there is my text (of which I know it is a number), and then the macro ends. Finally, as an additional obstacle, \parseme is really a `\csname b\@citeb\endcsname.

(A positive answer would also resolve Custom \thebibliography with alphabetic numbering for scrltt2 not working in presence of babel, at least in parts.)

  • Why can't you use \def rather than \edef? – cfr Nov 22 '14 at 22:02
  • @cfr I want to use the content of the macro and the idea with \edef was that it expands away the stuff I don't need. In contrast, \def does not expand anything, so the obstructing \let/\inthewayfalse stays where it is and I just have a new macro with a different name but the same problem as before. – bjoseru Nov 24 '14 at 10:32

An explicit number can be expanded without changing it and the unwanted command sequence can be redefined to vanish itself, when expanded:

% Setup
\def\bfoobar{\inthewayfalse 17}

% Extract the number from \csname b\@citeb\endcsname
% and store it in the macro \mynumber    
      \csname b\@citeb\endcsname

% Show the result in the console:
\typeout{My number is "\mynumber".}

The essential part is:

% same as:
% or

And the expansion gets rid of \intheway:

\edef\mynumber{\csname b\@citeb\endcsname}

The example puts this in a group to keep the redefinition of \inthewayfalse local.

  • Thanks, that work's for me! I appreciate the explanation, it makes all very clear to me now. – bjoseru Nov 24 '14 at 10:34

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.