20
votes
1answer
113 views

Is implicit `\relax` in conditionals explained anywhere in the TeXbook?

I have been relying for years on TeX's behavior where, say \if1\fi expands to nothing and \if1\else\fi does the same. In the second case TeX inserts an 'implicit' \relax when it tries to expand \else. ...
8
votes
1answer
189 views

Expandable, standard TeX only way to compare balanced token lists

Is there a (reasonably) efficient macro that does something similar to \long\def\comparets#1#2{\def\aa{#1}\def\bb{#2}\ifx\aa\bb true\else false\fi} except is expandable (i.e. ...
36
votes
4answers
2k views

How does your mind bend \expandafter to its will?

Expansion is often cited as one of the most arcane aspects of TeX, more akin to witchcraft than to something easily picked up by the newcomer. There are many great questions and great answers about ...
17
votes
2answers
348 views

Why does this simple \ifx test fail?

This should be easy, but I don't understand why the test below fails... I expected Hurrah! to be printed when the \currentchar count reaches 90 (i.e. the character code of Z). There must be some ...
42
votes
4answers
1k views

What is “expansion”?

I'm relatively new to (La)TeX, but I have a reasonable amount of experience with computational programming languages. Until I began learning (La)TeX, I'd never heard of "expansion"... So, what is ...
5
votes
2answers
71 views

How to get character code defined with \let (! Improper alphabetic constant)

Here's a example with the "! Improper alphabetic constant" error: %% this is ok \newcount\mychar \mychar=\number`a\relax \showthe a % shows You can't use `the letter a' after \the ...
4
votes
1answer
73 views

Expanding a variable within a protected label

I have some trouble with expanding variables within a protected label. I need a automatisated caption with a label all inside a command. Within the caption I want to have a two digit number ...
10
votes
1answer
72 views

\toks register expansion issue - or is it?

I am trying to assemble a table that occurs multiple times throughout a document. It always consists of some fixed columns, followed by a set of columns that appear in one table but are not needed in ...
4
votes
1answer
59 views

Can I expand a macro argument once without using a scratch register?

I'm still trying to get my head around how expansion works in TeX. One thing I can't figure out is how to expand a macro argument once without having to use a scratch register as an intermediate. As ...
4
votes
2answers
187 views

Some misunderstanding about macro expansion

I have the following code which doesn't work: \documentclass[12pt]{article} \tracingcommands=2 \tracingmacros=2 \tracingall \makeatletter \let\sep\relax \def\put@stack@#1#2{\edef#2{#1\sep#2}} ...
3
votes
1answer
66 views

Moving arguments inside group

I have a setup similar to the MWE below in which I have a macro that needs to be called in the document, and also regularly becomes a moving argument (in this case, inserted into the index, though it ...
9
votes
3answers
139 views

Problem with ^^<HEX>

I have small problem with ^^<HEX>. If I have a <HEX> part of the ^^<HEX> in the macro \def\attemp{<HEX>}, I cannot write ^^<HEX> as ^^\attempt or ...
11
votes
4answers
164 views

Partially expanding a command

My \john command is defined like so: \def\john{\DontExpandMe} I would now like to repeatedly change its definition, to keep adding some extra stuff on the front. \foreach\i in {ape,bat,cow,dog} { ...
4
votes
2answers
118 views

List of tokens from TeX mouth

Is it possible to get list of tokens which comes from TeX "mouth"? If I understand correctly: in mouth all macros, conditionals and special operations (like \the and \input) are expanded and then goes ...
15
votes
3answers
288 views

Parsing strings containing diacritical marks (macros?)

I apologize that this question may seem very much like several other recent ones I have asked (Parsing leading hardspaces, Parsing a \$ as part of an improved \getargs command). They are all related ...
5
votes
2answers
164 views

Variadic arguments macro

I am trying to make macro with variadic arguments, iterating over them. The final result is supposed to be: \foreach[x]((var = \x )){foo}{bar}{baz}\null evals to var = foo var = bar var = baz My ...
7
votes
2answers
114 views

Is there a way of defining a command \nullifyifmoved{arg} that will normally act like its argument but act like a no-op if the macro is “moved”?

I'm interested in a macro \nullifyifmoved that takes one argument arg and acts like arg in normal contexts, except it acts like a no-op wherever it is written to a file. Some background: Martin ...
5
votes
3answers
135 views

Metacommand for commands that dynamically select a parameter?

Original question I would like to create a metacommand for creating new projection commands. Specifically, \newproj{\cmd}{<n>}{<m>} should create \cmd as a new command of <n> ...
4
votes
1answer
81 views

Error with expansions

I am getting an error while trying to compile this minimal example: min.cls: \ProvidesClass{min} \LoadClass{minimal} \NeedsTeXFormat{LaTeX2e} \newenvironment{myenv}{}{ \def\aaa{test } ...
41
votes
3answers
1k views

Advantages and disadvantages of fully expandable macros

As I currently understand them, fully-expandable macros are analogous to pure/effect-free functions in functional programming. Correspondingly, things that are not expandable, such as \def, are ...
24
votes
3answers
839 views

How to know whether or not we need \expandafter?

The following is quoted from Peter Grill's answer on question LaTeX dynamic macro definition. The \expandafter is requried as the \newcommand needs to be dealt with after the \csname. As a ...
27
votes
1answer
404 views

Why six \noexpand in a row?

Trying to understand TeX's rules for parsing dimensions, I came up with the following weird behaviour: \dimen0=1\noexpand\noexpand\noexpand\noexpand\noexpand\empty pt is valid, but ...
10
votes
3answers
261 views

Expandable 'character scanning' command that preserves spaces

David Carlisle recently offered a clean and rather elegant TeX solution to a question about expandable 'character scanning' commands. Unfortunately, David's solution does not preserve spaces in the ...
59
votes
1answer
2k views

A LaTeX log analyzer application (visualizing TeX expansion)

Consider the following MWE, test.tex: \documentclass[12pt]{article} \begin{document} \tracingassigns=1 \tracingmacros=1 \def\aaa{something} \def\bbb{else \aaa, else} \edef\ccc{third \bbb, level} ...
7
votes
1answer
703 views

A \typeout (or expandable command) that can expand once - or with variable levels of expansion?

Consider the following MWE: \documentclass[12pt]{article} \begin{document} \def\aaa{something} \typeout{=1==\aaa==} \typeout{=1==\meaning\aaa==} \typeout{} \def\bbb{else \aaa, else} ...
2
votes
2answers
277 views

An expandable 'character scanning' command?

Please consider the following MWE, for a "character scanning" command "\looper" which utilizes \@tfor: \documentclass{minimal} \usepackage{trace} \makeatletter \newcommand\looper[1]{% % ...
3
votes
1answer
197 views

Showing expanded `\let` command with `\typeout`

I have already seen the related page macros - What is the difference between \let and \edef?, but I'm afraid it still doesn't expain to me the following MWE: \documentclass{minimal} ...
5
votes
2answers
397 views

On unprotecting (expanding) \protected macros (or, “the space after command name”)

I quite often come into a situation, where I need to obtain some text produced by a package macro as a string, like in say: Expanding (edef) a lipsum command? How do I "unprotect" an ...
8
votes
2answers
167 views

Execute non-expandable code inside a tabular environment

As there is no Expandable version of \InputIfFileExists or \IfFileExists, the question arises whether it is possible to execute non-expandable code in a tabular environment after all: File main.tex: ...
8
votes
2answers
479 views

Force the expansion of a macro parameter without \edef or \xdef

Two days I am looking for a solution but I have no more idea. This is my problem. I'm trying to create a macro to automatically define new other macros to write references in a document. I want to ...
11
votes
2answers
453 views

\expandafter within a \begingroup … \endgroup [duplicate]

Possible Duplicate: What does \begingroup\expandafter…\endgroup do? In many of Heiko Oberdiek's packages one sees this type of construction: ...
6
votes
1answer
162 views

How to extend the \romannumeral-based \fullyexpand to handle empty/all-space arguments?

In Expandable full expansion of tokens that preserves catcodes, Joseph Wright presents the following code: \long\def\fullyexpand#1{% \csname donothing\fullyexpandauxi{#1}{}% } ...
17
votes
2answers
293 views

Get the lion to run in loops. Tersely

Various constructions can cause TeX (aka the lion) to go into an infinite loop. The simplest example is \def~{~}~, which defines ~ to expand to itself, then expands it. Now, if we exclude macro ...
15
votes
4answers
576 views

Detokenizing without extra spaces?

I have a need to pass through potentially arbitrary characters untouched and found this macro: \def\test#1{\expandafter\zap@space\detokenize{#1} \@empty} The problem is that \detokenize inserts ...
9
votes
1answer
989 views

Expansion in \numexpr…\relax versus \pdfstrcmp

The \numexpr...\relax construction in eTeX allows to evaluate numerical expressions, and it expands tokens fully as it goes. The \pdfstrcmp{...}{...} construction in pdfTeX lets us compare two lists ...
54
votes
3answers
1k views

Why isn't everything expandable?

TeX's macro processor does its work in a process called expansion. For an input stream of tokens, the macro processor repeatedly expands them until non-expandable tokens remain. The resulting stream ...
21
votes
4answers
461 views

Can one define an expandable command that removes control sequences from its argument?

I am trying to create an expandable command that accepts a single argument that may contain control sequences, and expands to that same argument with all control sequences and braces removed. That is: ...
6
votes
1answer
348 views

Use \csname … \endcsname to compute the starred-version of some command

I want to define some commands declaring paired delimiters using the mathtools package in LaTeX. For example, \paren{...} should result in \left(...\right), whereas \paren[Big]{...} should give ...
13
votes
3answers
470 views

TeX macro and command expansion?

I have implemented couple of macros that should remove commas from numbers. It's nasty dirty stuff, but it works when input is number: \removecommas{12,34,56.7} % => 123456.7 But it stop working ...
8
votes
4answers
263 views

Does macros get applied to the source code before compilation?

I wonder if this is true. The latex compiler first run though the document, and search for all the macro declarations. the compiler then go though the document, apply each macro as a string ...
25
votes
4answers
561 views

Why isn't a command defined by \newcommand with an optional argument expandable?

In trying to fix a problem with a nested macro repeatedly calling itself, I tried expanding the inner call before passing it as an argument to the outer one. This failed miserably because the macro ...
6
votes
1answer
739 views

How do I examine a token?

... let me count the ways. I can test it with \if and \ifx and \show its \meaning And there I stop, both in my knowledge and my poetic ability (though some might argue that the latter never ...
16
votes
3answers
867 views

Does `\noexpand` have to be a primitive?

Background: I'm trying to deepen my understanding of TeX and how the intricacies work (spurred a little by this place, I should say, and hoping one day to not be a "Cargo Cult Programmer" - see When ...
12
votes
3answers
315 views

Expansion of first token in a tabular cell

Background I currently do some work on the collcell package which collects the content of a tabular/array cell and provides it to a user defined macro, e.g. using ...
8
votes
2answers
265 views

reversing the order of expansion

Is there a non-expl3 expandable function for reversing the order of expansion of an arbitrary number of tokens or macros? For example, \reverseexpansion<n>\a\b ...
17
votes
5answers
1k views

Are there purely expandable variants of \MakeUppercase?

\MakeUppercase and \uppercase use TeX's uccode, and they are not purely expandable. Say, \edef\temp{\MakeUppercase{abc}} will fail. Sometimes purely expandable macros are very useful. They are ...
11
votes
1answer
545 views

How to do \scantokens inside \edef without triggering “Runaway definition”

I'm trying to find a way to use the e-TeX \scantokens command inside [the equivalent of] an \edef (well, actually an \xdef, but presumably this does not make any real difference since that's just the ...
7
votes
3answers
192 views

Are we inside an edef?

How would you test whether we are in an expansion only context (i.e., \edef, \xdef, \write,...) or not? The only ways I could think of leave things behind (but the full expansion of that extra stuff ...
5
votes
2answers
390 views

Using \input vs. \scantokens in section title (with package hyperref)

I meet the following issue when trying to use \scantokens in section titles, together with the hyperref package (whithout this package, all is fine). \protect\input... can appear in a section title. ...
11
votes
2answers
691 views

Tricks to make macros expandable

Expandable macros are useful (I find working in the lion's mouth super cool). But they are difficult to write. Can more experienced users give hints that help achieve expandability? For example, we ...