\ifnum\secno < 1 \secno=11 \excnt=34 \fi \section Referring to examples and labeled parts of examples \nobreak\vskip-2ex \subsection*Unnamed reference \deftagsec{unnamedref} \begininventory \macros \idx{|\lastx|}, \idx{|\nextx|}, \idx{|\blastx|}, \idx{|\anextx|}, \idx{|\bblastx|}\endmc \endinventory \noindent If $x$ is the value of |\excnt|, these macros produce $x-1$, $x$, $x-2$, $x+1$, $x-3$, respectively, expressed as an either an arabic or roman numeral, depending on the setting of |exnotype|. The example number counter is incremented early in the expansion of |\ex| and |\pex|, so if one of these macros is used inside an example, ``last example'' has the meaning ``current example number''. Although |\excnt| is incremented early, it is incremented after local parameters are set. Consequently, if any of these macros is used in setting parameters in the optional argument of |\ex| or |\pex|, it acts as if it were being evaluated just before |\ex| or |\pex|. It is potentially dangerous to use macros like |\bblastx| or |\anextx| for reference to an example because later additions or deletions in the document can throw off the reference. This kind of misreference is particularly easy to overlook in proofing a document. It is better to assign names to the things you want to refer to and to refer to them by name, particularly in a document that will undergo a lot of rewriting. If reference by name is used and an intervening example is deleted or added, no problem arises. If the example which is referred to is deleted, then \Tex\ will report a missing reference. \subsection Named reference \deftagsec{named-reference} \begininventory \macros \idx{|\deftag|}, \idx{|\deftagex|}, \idx{|\deftaglabel|}, \idx{|\deftagpage|}, \idx{|\getref|}, \idx{|\getfullref|}\endmc \parameters* \idx{|tag|}& character string& \hfil (none)\cr \endinventory \noindent The core macros are \idx{|\deftag|} and \idx{|\getref|}. |\deftag| takes two (obligatory) arguments. After |\deftag{«reference»}{«tag»}| is executed, |\getref{«tag»}| expands to {\sl reference}, where the value of the reference is determined at the point the |\deftag| command was evaluated. \idx{|\deftagex|}|{«tag»}| expands to |\deftag{\the\exno}{«tag»}|. \idx{|\deftagpage|}|{«tag»}| expands to |\deftag{\the\pageno}{«tag»}|, but the expansion is delayed until after \Tex's page breaking mechanism has decided what page the |\deftag| command appears on. The tag/page pair which is generated in this case is written to a file only, so |\getref| cannot recover a page number until a tag-ref file is read. The evaluation of \idx{|\deftaglabel|}|{«tag»}| is more complex. |\pexcnt|, the setting of |labeltype|, and the setting of |everylabel| are used to construct the reference (either a letter or a number). The tag which is submitted to |\deftag| is $\sl tag'\!|.|tag$, where $\sl tag'$ is the example number tag. The code below produces (\nextx). \codedisplay \pex[interpartskip=0pt] \a First\deftag{the first part of example \lastx}{FP} \a Second\deftagex{snoopy}\deftaglabel{dog} \a Third\deftaglabel{a} \xe|endcodedisplay \framedisplay~ \pex[interpartskip=0pt] \a First\deftag{the first part of example \lastx}{FP} \a Second\deftagex{snoopy}\deftaglabel{dog} \a Third\deftaglabel{a} \xe \endframedisplay \noindent Afterwards, assuming that the tag |snoopy| has not been redefined in the interim\par\nobreak\medskip \hskip3em \vtop{\openup1pt \halign{#\hfil& \quad$\to$\quad #\hfil\cr |\getref{snoopy}|& \getref{snoopy}\cr |\getref{snoopy.dog}|& \getref{snoopy.dog}\cr |\getfullref{snoopy.dog}|& \getfullref{snoopy.dog}\cr |\getref{snoopy.a}|& \getref{snoopy.a}\cr |\getfullref{snoopy.a}|& \getfullref{snoopy.a}\cr |\getref{dog}|& \it undefined tag warning, or spurious reference\cr |\getref{FP}|& \getref{FP}\cr }} \medskip \noindent |\getref{dog}| will produce a spurious reference if the tag |dog| is defined somewhere else in your document. |\deftaglabel| must know, at the point that it is expanded, what tag has been attached to the example number. If the example number has not been tagged at that point, a warning message is issued. There are two alternatives to the explicit use of |\deftagex| and |\deftaglabel|. One is the use of the parameter |tag|. After \codedisplay \pex[interpartskip=0pt,labeltype=alpha,tag=snoopy] \a First \a[tag=dog] Second \a Third\deftaglabel{A} \xe |endcodedisplay \noindent |\getref{snoopy}|, |\getref{snoopy.dog}|, and |\getref{snoopy.A}| are interpreted as expected, as are |\getfullref{snoopy.dog}| and |\getfullref{snoopy.A}|. The other alternative is a special ``tagging notation'' which, unlike most shortcuts, makes the code easier to read as well. After \codedisplay \pex[interpartskip=0pt,labeltype=alpha] \a First \a Second \a[tag=A] Third \xe |endcodedisplay \noindent |\getref{snoopy}|, |\getref{snoopy.dog}|, and |\getref{snoopy.A}| are interpreted as expected, as are |\getfullref{snoopy.dog}| and |\getfullref{snoopy.A}|. If |\getref{sometag}| is evaluated and the tag is undefined, a warning message to this effect is generated and~\hbox{$\bullet$|sometag|} is typeset instead of the intended reference. \subsection Proofing references \begininventory \macros* |\refproofing|\endmc \endinventory It is tedious to check that references to example numbers and the like are correct (i.e. refer to what you think they refer to). \ExPex\ provides a little help. If you execute \idx{|\refproofing|}, then all the references that are generated by |\bblastx|, |\blastx|, |\lastx|, |\nextx|, |\anextx|, |\getref|, and |\getfullref| are highlighted. If \PSTricks\ is loaded at the point that |\refproofing| is evaluated, the highlighting consists of a box around the reference. If not, the reference is under- and overlined. Highlighting is helpful in copy editing. The difference is illustrated below. \pex \a Consider (\getfullref{snoopy.dog}), for example.\qquad default behavior \refproofing \a Consider (\getfullref{snoopy.dog}), for example.\qquad |\refproofing|, \PSTricks\ available \a {\let\PSTricksLoaded\relax \refproofing \makeatletter \let\@highlightprint\mathhigh@lightref \resetatcatcode Consider (\getfullref{snoopy.dog}), for example.}\qquad |\refproofing|, \PSTricks\ not available \xe \subsection The tag/reference file \begininventory \macros \idx{|\gathertags|}, \idx{|\tagfilesuffix|}\endmc \endinventory \noindent Forward references require writing tag/reference associations to a file in one run, then reading this file in a second run. Forward reference is only one reason for such a system. If you work on a document in pieces, say one section at a time, and need to refer to things in prior sections, then the tag/reference pairs from previous sections must be stored in a file so that they can be used in the section that you are working on. If you say \idx{|\gathertags|}, the tag/reference pairs will be written to a file as they are established. If your main file is named {\sl foop.tex}, for example, the default is to write the tag/ref pairs to {\sl foop-tags.tex}. But you can modify this by using the command \idx{|\tagfilesuffix|}. \slname{expex.tex} contains |\tagfilesuffix{-tags}|, but you can overrule this with |\tagfilesuffix{«your suffix»}|. When the first |\getref|, |\getfullref|, or |\gathertags| command is encountered, \ExPex\ checks to see if there is a tag file. If the file does exist, it is read and all the tag/reference pairs it encodes are established. No testing is done for conflicting tag/reference pairs with the same tag, so it is the responsibility of the user to see that this does not occur to a bad effect. If the user wants to be absolutely sure that bad references have not accidentally occurred because of using the same tag twice, he/she can look directly at the tag file in a text editor. If the lines are alphabetized, it is relatively easy to find tags for which multiple references have been established. If you are a careful copy editor, this may be worth doing in a complex project (a book length manuscript) during final copy editing. Of course, the printed final manuscript should be checked in any event to make sure that the references refer to what you want them to refer to. For what it is worth, my own style of work is to break up projects into multiple pieces and have a main file which calls the various pieces. Then I simply comment out the calls to pieces that I am not working on. From time to time I will run the main file calling on all the various pieces, invoking |\gathertags|. Then I comment out |\gathertags|. The tag-ref file which is created then remains intact until |\gathertags| is invoked at some future time. All of the tag/reference pairs it encodes are available in subsequent work until a new tags file is created. \subsection References to references, references as values \begininventory \macros* \idx{|\lastlabel|}\endmc \endinventory % If, for some reason, you want to refer to a specific part of a multipart example without tagging the example number, it can be done as follows, assuming that the part labels are alphabetical. \codedisplay \pex[everylabel=\it] \a First Example. \a Second Example.\deftag{\lastx\lastlabel}{snoopy} \a Third Example. \xe |endcodedisplay \framedisplay \pex[everylabel=\it] \a First Example. \a Second Example.\deftag{\lastx\lastlabel}{snoopy} \a Third Example. \xe \endframedisplay \noindent You can then use |\getref{snoopy}| to retrieve \getref{snoopy}. |\lastlabel| expands to the most recent label, in the form in which it is printed (i.e. containing the expansion of |\everylabel|). If the part labels are numerical, then |\deftag{\lastx.\lastlabel}| is required. You can also say: \sidx{|exno|, setting by reference}% \codedisplay \ex[exno=\getref{snoopy}] Second example.\xe|endcodedisplay \framedisplay~ \ex[exno=\getref{snoopy}] Second example.\xe \endframedisplay \medskip Or you can say: \codedisplay \ex[exno={\getref{snoopy}, repeated},exnoformat={[X]}] Second example.\xe |endcodedisplay \framedisplay~ \ex[exno={\getref{snoopy}, repeated},exnoformat={[X]}] Second example.\xe \endframedisplay % Braces must hide the comma in the value which sets the key. If you say \codedisplay \pex[labeltype=numeric] \a First Example. \a Second Example. \a Third Example. \xe|endcodedisplay \framedisplay~ \pex[labeltype=numeric] \a First Example. \a Second Example. \a Third Example. \xe \endframedisplay \noindent then, if you want to repeat (\getfullref{dog.G}) at some point, you can use: \codedisplay \ex[exno=\getfullref{dog.G}] Second example\xe |endcodedisplay \framedisplay~ \ex[exno={\getfullref{dog.G}}] Second example\xe \endframedisplay \subsection Extensions of the tag/reference mechanism The tag/reference mechanism can easily be extended to reference to chapters, sections, and subsections. Suppose, for example, that there are counters for the chapter number, section number, subsection number, and subsubsection number. One might define: \codedisplay \def\currsec{\the\chapterno \ifnum\secno>0 .\the\secno \ifnum\subsecno>0 .\the\subsecno \ifnum\subsubsecno>0 .\the\subsubsecno \fi\fi\fi} \def\deftagsec#1{\deftag\currsec{#1}}|endcodedisplay \noindent This assumes that there are counters |\chapterno|, |\secno|, |\subsecno|, and |\subsecsecno| and that when a chapter is initiated, |\secno| is set to 0, when a section is initiated, |\secsecno| is set to 0, and that when a subsection is initiated, |\subsubsecno| is set to 0. (Lines 1--5, commented out, are included at the end of {\sl expex.tex\/} for the user to use, modify, or ignore.) \subsection The parameter {\tt fullreformat} \begininventory \parameters* \idx{|fullrefformat|}& $\ldots\,|X|\,\ldots\,|A|\,\ldots$ & |XA|\cr \endinventory \begingroup \parindent=0pt \leftskip=1.2em 1. |labelformat| (see page \getref{labelformatpage}) determines how the labels are formatted. Generally they are followed by a period, but this parameter allows other possibilities. \smallskip 2. |fullrefformat| determines how references retrieved by |\getfullref| are formatted. Generally, example numbers and labels are concatenated if the labels are characters and separated by a period if the labels are numbers. This parameter allows other possibilities. The format specification is primitive. The value of |fullrefformat| is analyzed as |#1X#2A#3|, with |X| preceding |A|. Then the full reference is found by substituting the example number for |X| and the part label for |A|. \smallskip \endgroup Consider the artificial example below, with unusual formatting for illustrative purposes. \begingroup \setss .65 .35 \beginss \pex[labeltype=numeric,labelformat={[A]}, fullrefformat=X-A,samplelabel={[1]}] \a first \a second \xe|midss \pex[labeltype=numeric,labelformat={[A]}, fullrefformat=X-A,samplelabel={[1]}] \a first \a second \xe \endss \endgroup |\getref{K.A}| produces \getref{K.A} and |\getfullref{K.A}| produces \getfullref{K.A}. \subsection Reference to a part of a multipart example Suppose there is a multipart example which you want to partially repeat at a later point, giving only some of the parts. There are many opportunities to make a mistake. The reference to the example number may be wrong, the references to the part labels my be wrong, or a particular part may not be repeated the way it originally appeared. Here is one way to (partially) automate the references to avoid most of the possible reference errors. \begingroup \setss .53 .43 \beginss \deftag{Someone loves everyone.}{1st} \deftag{Everyone loves someone.}{2nd} \pex \a \dots \a \getref{1st} \a \dots \a \getref{2nd} \xe \ex An intervening example.\xe The two crucial examples in (\getref{A}) are repeated below: \pex[exno=\getref{A}] \a[label=\getref{A.X}] \getref{1st} \a[label=\getref{A.Z}] \getref{2nd} \xe \ex Numbering resumes.\xe|midss \deftag{Someone loves everyone.}{1st} \deftag{Everyone loves someone.}{2nd} \pex \a \dots \a \getref{1st} \a \dots \a \getref{2nd} \xe \bigskip \ex An intervening example.\xe \bigskip The two crucial examples in (\getref{A}) are repeated below: \bigskip \deftag{\the\secno.\the\subsecno}{explicit-sec}% \pex[exno=\getref{A}] \a[label=\getref{A.X}] \getref{1st} \a[label=\getref{A.Z}] \getref{2nd} \xe \bigskip \ex Numbering resumes.\xe \endss % {\bf Important limitation}:\enspace Inside an example that sets |exno| to a nonempty value, the use of |\deftaglabel| or |\deftagex|, or their implicit versions using the |<|\dots|>| notation, or |\label|, will result in an error or (more dangerously) an unexpected outcome. This is a minor limitation because there should be no need to tag items which themselves are referenced by tags. It is important only because violating it can generate Tex errors.\endgroup \subsection Support for the LaTex \ttcs{label} and \ttcs{ref} commands% \deftag{\the\secno.\the\subsecno}{labelsec} \sidx{|\label|, use of the LaTex macro} \sidx{|\ref|, use of the LaTex macro} \noindent LaTex users, if so inclined, may wish to use the LaTex |\label|-|\ref| mechanism to tag example numbers and example part labels. Assuming that LaTex is in use, \beginss \pex \label{A} \a Tom\label{B} \a Dick\label{C} \a Harry\label{D}, etc. \xe \ex~ Intervening example.\xe \noindent Consider example (\ref{A}). Tom is in example (\ref{B}), Dick is in example (\ref{C}), and Harry is in example (\ref{D}).|midss %%%% \pex[aboveexskip=1ex,nopreamble]\deftagex{A} \a Tom\deftaglabel{B} \a Dick\deftaglabel{C} \a Harry\deftaglabel{D}, etc. \xe \bigskip \ex~ Intervening example\xe \bigskip \noindent Consider example (\getref{A}). Tom is in example (\getfullref{A.B}), Dick is in example (\getfullref{A.C}), and Harry is in example (\getfullref{A.D}). \medskip %%%% \endss There are important differences between the LaTex mechanism and the |\deftag|-|\getref| mechanism. \smallskip \noindent 1.\enspace |\ref{|{\it tag}|}| cannot be used as a special example number, nor can it be given as an optional argument to |\a|. \smallskip \noindent 2.\enspace The |\label| name space is flat. No distinction is made between names of examples and names of parts of examples. This makes it much harder to remember and manage the names, at least for me. \smallskip \noindent 3.\enspace LaTex provides no control over the generation of the file containing the tag-reference pairs. One cannot work on Chapter 5 (for example) and have all the tag-reference information for the earlier chapters available without actually submitting all of the Chapters 1 to 4 to LaTex while you are working on Chapter 5.