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I'm not getting the output I want from my LaTeX code, and I think the problem is that I'm not expanding things at the right times.

Code

\documentclass{article} \usepackage{tikz} \usepackage{etextools} \makeatletter % The result of calling % \@defineLine{foo}{35} % is that the command \wickerson@foo@pos gets defined as 35. \newcommand*\@defineLine[2]{% \typeout{Defining wickerson@#1@pos = #2} \expandafter\xdef\csname wickerson@##1@pos\endcsname{#2} } % Project the pos-field from the line with the given % identifier. For instance, if \wickerson@foo@pos=35 then % \@getLinePos{foo} % will give 35. \xdef\@getLinePos#1{\csname wickerson@#1@pos\endcsname} % A comma-separated list of "active" lines. Each element is % a line identifier. \newcommand*\@activeLines{} % Add the given identifier to the list of active lines. \newcommand*\@addToActiveLines[1]{% \ifx\@activeLines\@empty\else\g@addto@macro\@activeLines{,}\fi \g@addto@macro\@activeLines{#1} } % Remove the given identifier from the list of active lines. \newcommand*\@removeFromActiveLines[1]{% \@expandtwoargs\@removeelement{#1}\@activeLines\@activeLines } % Print each active line identifier, associated with its % corresponding pos field. Typical output: % {a ↦ 10, b ↦ 30, c ↦ 50, d ↦ 70,} \newcommand*\@printState{% Current state: $\{ \foreach\i in \@activeLines {% \i \mapsto \@getLinePos\i, } \}$ \par } \begin{document} \foreach \x/\xvalue in {a/10, b/30, c/50, d/70} { \ExpandNextTwo\@defineLine{\x}{\xvalue} \ExpandNext\@addToActiveLines{\x} \@printState } \foreach \x in {a, c} { \ExpandNext\@removeFromActiveLines{\x} \@printState } \end{document}

Explanation

The first foreach-loop cycles over a list of pairs, building up a function from identifiers (e.g. a,b,etc.) to numbers. The values of this function are stored in a series of macros (e.g. \wickerson@a@pos stores the value of the function for identifier a), and the domain of this function is the comma-separated list \@activeLines. Initially \@activeLines is empty, and by the end it is a,b,c,d.

I print my function after each iteration of the loop. By the end I expect to print

{a↦10, b↦30, c↦50, d↦70}

but instead it prints

{a↦70, b↦70, c↦70, d↦70}

I suspect the problem is when I add a mapping to my function, I'm not expanding the value enough, and so it changes when I add another mapping. I thought using ExpandNextTwo from etextools would expand everything nicely, but it doesn't seem to have helped. Any ideas?

The second foreach-loop tries to remove some of the mappings from my function, with the help of the \@removeelement command. Unfortunately, it doesn't work. The mapping is only removed within the scope of the current loop iteration, and by the next iteration, the mapping has returned. I suspect the problem is that the \@removeelement is not redefining \@activeLines globally, but I don't know how to fix this. Any ideas? (I hope I don't need to switch to the expl3 syntax to achieve this, because that would be require quite a drastic change to my code!)

Current output

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Desired output

enter image description here

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2 Answers 2

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20

The following two macros need fixing:

\newcommand*\@defineLine[2]{% \typeout{Defining wickerson@#1@pos = #2} \expandafter\xdef\csname wickerson@##1@pos\endcsname{#2} }

That will define for \@defineLine{a}{10} the macro \wickerson@#1@pos instead of \wickerson@a@pos. Fix:

\newcommand*\@defineLine[2]{% \typeout{Defining wickerson@#1@pos = #2} \expandafter\xdef\csname wickerson@#1@pos\endcsname{#2} }

The next macro uses it:

% Project the pos-field from the line with the given % identifier. For instance, if \wickerson@foo@pos=35 then % \@getLinePos{foo} % will give 35. \xdef\@getLinePos#1{\csname wickerson@#1@pos\endcsname}

Since \xdef expands, \csname is executed to \wickerson@#1@pos with #1 part of the macro name, not an argument. Fix:

\gdef\@getLinePos#1{\csname wickerson@#1@pos\endcsname}

Getting rid of the last comma

A feature of \foreach can be used to get rid of the latest comma in the output:

\newcommand*\@printState{% Current state: $\{ \foreach\i [count=\ii] in \@activeLines {% \ifnum\ii>1 ,\fi \i \mapsto \@getLinePos\i } \}$ \par }

Result

Removing

The question uses the following definition for removing elements:

\newcommand*\@removeFromActiveLines[1]{% % \@expandtwoargs\@removeelement{#1}\@activeLines\@activeLines % } %

Indeed, the effect of LaTeX's \@removeelement is limited to the current group. If you want to make the changes of \@activeLines global, then \global\let helps:

\newcommand*\@removeFromActiveLines[1]{% % \@expandtwoargs\@removeelement{#1}\@activeLines\@activeLines % \global\let\@activeLines=\@activeLines } %
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  • Thank you so much Heiko. Your explanations are extremely clear to me. Commented May 16, 2013 at 19:37
  • So I wasn't actually defining \wickerson@a@pos, \wickerson@b@pos, etc, but instead defining \wickerson@#1@pos over and over again. Heh. Commented May 16, 2013 at 19:53
  • Transparent PNG background... I like it. Commented May 16, 2013 at 20:19
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    @Werner Thanks. The transparent background is the result of ImageMagick's convert from PDF to PNG. It uses Ghostscript with device pngalpha. Commented May 16, 2013 at 20:26
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    @JohnWickerson Answer updated (using \global\let\@activeLines=\@activeLines). Commented May 17, 2013 at 12:46
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I believe that with expl3 it's more straightforward, since it doesn't rely on knowing what's needed to expand and when.

\documentclass{article} \usepackage{xparse} \ExplSyntaxOn \seq_new:N \l_wickerson_list_seq \NewDocumentCommand{\printState}{>{\SplitList{,}}m} { \seq_clear:N \l_wickerson_list_seq \ProcessList{#1}{\splitatslash} Current~state\tl_to_str:n { : } ~ % $\seq_use:Nnnn \l_wickerson_list_seq { , } { , } { , }$ } \NewDocumentCommand{\splitatslash}{>{\SplitArgument{1}{/}}m} { \wickerson_split_element:nn #1 } \cs_new_protected:Npn \wickerson_split_element:nn #1 #2 { \seq_put_right:Nn \l_wickerson_list_seq { #1 \mapsto #2 } } \ExplSyntaxOff \begin{document} \printState{a/10} \printState{a/10, b/30} \printState{a/10, b/30, c/50} \printState{a/10, b/30, c/50, d/70} \end{document}

enter image description here

A different implementation that makes it possible to remove states; I've used both a sequence for the "before slash" parts and a property list that holds the vaule ("after slash").

The command \defineStates reinitializes the variables, while \addStates put new states in the variables; similarly, \removeStates removes states. Finally, \printStates just gives a visual representation of the states.

\documentclass{article} \usepackage{xparse} \ExplSyntaxOn %%% variables \seq_new:N \g_wickerson_list_seq \prop_new:N \g_wickerson_states_prop %%% document commands \NewDocumentCommand{\defineStates}{m} { \wickerson_definestates:n { #1 } } \NewDocumentCommand{\addStates}{m} { \wickerson_addstates:n { #1 } } \NewDocumentCommand{\removeStates}{m} { \clist_map_inline:nn { #1 } { \seq_gremove_all:Nn \g_wickerson_list_seq { ##1 } % The following also removes the state from the property list % You can choose whether keep it or comment it out \prop_gremove:Nn \g_wickerson_states_prop { ##1 } } } \NewDocumentCommand{\printStates}{} { Current~state\tl_to_str:n { : } ~ % $ \seq_map_inline:Nn \g_wickerson_list_seq { ##1 \mapsto \prop_get:Nn \g_wickerson_states_prop { ##1 }, } $ } %%% internal commands \cs_new_protected:Npn \wickerson_addstates:n #1 { \clist_map_inline:nn { #1 } { \wickerson_split_element:ww ##1 \q_stop } } \cs_new_protected:Npn \wickerson_definestates:n #1 { \seq_gclear:N \g_wickerson_list_seq \prop_gclear:N \g_wickerson_states_prop \wickerson_addstates:n { #1 } } \cs_new_protected:Npn \wickerson_split_element:ww #1 / #2 \q_stop { \seq_gput_right:Nn \g_wickerson_list_seq { #1 } \prop_gput:Nnn \g_wickerson_states_prop { #1 } { #2} } \ExplSyntaxOff \begin{document} %% Initialize \defineStates{a/10,b/30}\printStates %% Add new states \addStates{c/50}\printStates \addStates{d/70,e/90}\printStates %% remove some states \removeStates{a,c}\printStates \end{document}

enter image description here

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  • I think it would be more natural to use a delimited function at the expl3 level, not xparse. Namely, \cs_new_protected:Npn \wickerson_split_element:ww #1 / #2 \q_stop {...}. Commented May 17, 2013 at 12:48
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    @BrunoLeFloch I agree, but I wanted to use less expl3 as possible. I'll provide a "full" `expl3 version later. Commented May 17, 2013 at 12:53
  • I'm trying to learn more about this expl3 stuff, but so far have only found a short introduction (here). Where can I learn about things like what {>{\SplitList{,}}m} means? Commented May 18, 2013 at 15:46
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    @JohnWickerson That's in the documentation of xparse: texdoc xparse Commented May 18, 2013 at 15:47
  • Note that as of September 2014, \prop_get:Nn has been renamed to \prop_item:Nn Commented Sep 17, 2014 at 17:58

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