% rail.sty - style file to support railroad diagrams

 %

 % 09-Jul-90 L. Rooijakkers

 % 08-Oct-90 L. Rooijakkers	fixed centering bug when \rail@tmpc<0.

 % 07-Feb-91 L. Rooijakkers	added \railoptions command, indexing

 % 08-Feb-91 L. Rooijakkers	minor fixes

 % 28-Jun-94 K. Barthelmann	turned into LaTeX2e package

 % 08-Dec-96 K. Barthelmann	replaced \@writefile

 % 13-Dec-96 K. Barthelmann	cleanup

 %

 % This style file needs to be used in conjunction with the 'rail'

 % program. Running LaTeX as 'latex file' produces file.rai, which should be

 % processed by Rail with 'rail file'. This produces file.rao, which will

 % be picked up by LaTeX on the next 'latex file' run.

 %

 % LaTeX will warn if there is no file.rao or it's out of date.

 %

 % The macros in this file thus consist of two parts: those that read and

 % write the .rai and .rao files, and those that do the actual formatting

 % of the railroad diagrams.

 \NeedsTeXFormat{LaTeX2e}

 \ProvidesPackage{rail}[1996/12/13]

 % railroad diagram formatting parameters (user level)

 % all of these are copied into their internal versions by \railinit

 %

 % \railunit : \unitlength within railroad diagrams

 % \railextra : extra length at outside of diagram

 % \railboxheight : height of ovals and frames

 % \railboxskip : vertical space between lines

 % \railboxleft : space to the left of a box

 % \railboxright : space to the right of a box

 % \railovalspace : extra space around contents of oval

 % \railframespace : extra space around contents of frame

 % \railtextleft : space to the left of text

 % \railtextright : space to the right of text

 % \railtextup : space to lift text up

 % \railjoinsize : circle size of join/split arcs

 % \railjoinadjust : space to adjust join

 %

 % \railnamesep : separator between name and rule body

 \newlength\railunit

 \newlength\railextra

 \newlength\railboxheight

 \newlength\railboxskip

 \newlength\railboxleft

 \newlength\railboxright

 \newlength\railovalspace

 \newlength\railframespace

 \newlength\railtextleft

 \newlength\railtextright

 \newlength\railtextup

 \newlength\railjoinsize

 \newlength\railjoinadjust

 \newlength\railnamesep

 % initialize the parameters

 \setlength\railunit{1sp}

 \setlength\railextra{4ex}

 \setlength\railboxleft{1ex}

 \setlength\railboxright{1ex}

 \setlength\railovalspace{2ex}

 \setlength\railframespace{2ex}

 \setlength\railtextleft{1ex}

 \setlength\railtextright{1ex}

 \setlength\railjoinadjust{0pt}

 \setlength\railnamesep{1ex}

 \DeclareOption{10pt}{

   \setlength\railboxheight{16pt}

   \setlength\railboxskip{24pt}

   \setlength\railtextup{5pt}

   \setlength\railjoinsize{16pt}

 }

 \DeclareOption{11pt}{

   \setlength\railboxheight{16pt}

   \setlength\railboxskip{24pt}

   \setlength\railtextup{5pt}

   \setlength\railjoinsize{16pt}

 }

 \DeclareOption{12pt}{

   \setlength\railboxheight{20pt}

   \setlength\railboxskip{28pt}

   \setlength\railtextup{6pt}

   \setlength\railjoinsize{20pt}

 }

 \ExecuteOptions{10pt}

 \ProcessOptions

 % internal versions of the formatting parameters

 %

 % \rail@extra   : \railextra

 % \rail@boxht   : \railboxheight

 % \rail@boxsp   : \railboxskip

 % \rail@boxlf   : \railboxleft

 % \rail@boxrt   : \railboxright

 % \rail@boxhht  : \railboxheight / 2

 % \rail@ovalsp  : \railovalspace

 % \rail@framesp : \railframespace

 % \rail@textlf	: \railtextleft

 % \rail@textrt	: \railtextright

 % \rail@textup	: \railtextup

 % \rail@joinsz  : \railjoinsize

 % \rail@joinhsz : \railjoinsize / 2

 % \rail@joinadj : \railjoinadjust

 %

 % \railinit : internalize all of the parameters.

 \newcount\rail@extra

 \newcount\rail@boxht

 \newcount\rail@boxsp

 \newcount\rail@boxlf

 \newcount\rail@boxrt

 \newcount\rail@boxhht

 \newcount\rail@ovalsp

 \newcount\rail@framesp

 \newcount\rail@textlf

 \newcount\rail@textrt

 \newcount\rail@textup

 \newcount\rail@joinsz

 \newcount\rail@joinhsz

 \newcount\rail@joinadj

 \newcommand\railinit{

 \rail@extra=\railextra

 \divide\rail@extra by \railunit

 \rail@boxht=\railboxheight

 \divide\rail@boxht by \railunit

 \rail@boxsp=\railboxskip

 \divide\rail@boxsp by \railunit

 \rail@boxlf=\railboxleft

 \divide\rail@boxlf by \railunit

 \rail@boxrt=\railboxright

 \divide\rail@boxrt by \railunit

 \rail@boxhht=\railboxheight

 \divide\rail@boxhht by \railunit

 \divide\rail@boxhht by 2

 \rail@ovalsp=\railovalspace

 \divide\rail@ovalsp by \railunit

 \rail@framesp=\railframespace

 \divide\rail@framesp by \railunit

 \rail@textlf=\railtextleft

 \divide\rail@textlf by \railunit

 \rail@textrt=\railtextright

 \divide\rail@textrt by \railunit

 \rail@textup=\railtextup

 \divide\rail@textup by \railunit

 \rail@joinsz=\railjoinsize

 \divide\rail@joinsz by \railunit

 \rail@joinhsz=\railjoinsize

 \divide\rail@joinhsz by \railunit

 \divide\rail@joinhsz by 2

 \rail@joinadj=\railjoinadjust

 \divide\rail@joinadj by \railunit

 }

 \AtBeginDocument{\railinit}

 % \rail@param : declarations for list environment

 %

 % \railparam{TEXT} : sets \rail@param to TEXT

 \def\rail@param{}

 \newcommand\railparam[1]{

 \def\rail@param{#1}

 }

 % \rail@tokenfont : format setup for \railtoken identifiers

 %

 % \rail@termfont : format setup for terminals

 %

 % \rail@nontfont : format setup for nonterminals

 %

 % \rail@annofont : format setup for annotations

 %

 % \rail@rulefont : format setup for rule names

 %

 % \rail@indexfont : format setup for index entry

 %

 % \railtermfont{TEXT} : set terminal format setup to TEXT

 %

 % \railnontermfont{TEXT} : set nonterminal format setup to TEXT

 %

 % \railannotatefont{TEXT} : set annotation format setup to TEXT

 %

 % \railnamefont{TEXT} : set rule name format setup to TEXT

 %

 % \railindexfont{TEXT} : set index entry format setup to TEXT

 \def\rail@termfont{\ttfamily\upshape}

 \def\rail@nontfont{\rmfamily\upshape}

 \def\rail@annofont{\rmfamily\itshape}

 \def\rail@namefont{\rmfamily\itshape}

 \def\rail@indexfont{\rmfamily\itshape}

 \newcommand\railtermfont[1]{

 \def\rail@termfont{#1}

 }

 \newcommand\railnontermfont[1]{

 \def\rail@nontfont{#1}

 }

 \newcommand\railannotatefont[1]{

 \def\rail@annofont{#1}

 }

 \newcommand\railnamefont[1]{

 \def\rail@namefont{#1}

 }

 \newcommand\railindexfont[1]{

 \def\rail@indexfont{#1}

 }

 % railroad read/write macros

 %

 % \begin{rail} TEXT \end{rail} : TEXT is written out to the .rai file,

 %                                as \rail@i{NR}{TEXT}. Then the matching

 %                                \rail@o{NR}{FMT} from the .rao file is

 %                                executed (if defined).

 %

 % \railoptions{OPTIONS} : OPTIONS are written out to the .rai file,

 %                         as \rail@p{OPTIONS}.

 %

 % \railterm{IDENT,IDENT,...} : format IDENT as terminals. writes out

 %                              \rail@t{IDENT} to the .rai file

 %

 % \railalias{IDENT}{TEXT} : format IDENT as TEXT. defines \rail@t@IDENT as

 %                           TEXT.

 %

 % \rail@nr : railroad diagram counter

 %

 % \ifrail@match : current \rail@i{NR}{TEXT} matches

 %

 % \rail@first :	actions to be done first. read in .rao file,

 %               open .rai file if \@filesw true, undefine \rail@first.

 %               executed from \begin{rail} and \railtoken.

 %

 % \rail@i{NR}{TEXT} : defines \rail@i@NR as TEXT. written to the .rai

 %                     file by \rail, read from the .rao file by

 %                     \rail@first

 %

 % \rail@t{IDENT} : tells Rail that IDENT is to be custom formatted,

 %                  written to the .rai file by \railterm.

 %

 % \rail@o{NR}{TEXT} : defines \rail@o@NR as TEXT, read from the .rao

 %                     file by \rail@first.

 %

 % \rail@p{OPTIONS} : pass options to rail, written to the .rai file by

 %                    \railoptions

 %

 % \rail@write{TEXT} : write TEXT to the .rai file

 %

 % \rail@warn : warn user for mismatching diagrams

 %

 % \rail@endwarn : either \relax or \rail@warn

 %

 % \ifrail@all : checked at the end of the document

 \newcount\rail@nr

 \newif\ifrail@all

 \rail@alltrue

 \newif\ifrail@match

 \def\rail@first{

 \makeatletter

 \InputIfFileExists{\jobname.rao}{}{\PackageInfo{rail}{No file \jobname.rao}}

 \makeatother

 \if@filesw

 \newwrite\tf@rai

 \immediate\openout\tf@rai=\jobname.rai

 \fi

 \global\let\rail@first=\relax

 }

 \long\def\rail@body#1\end{

 \begingroup

 \let\\=\relax

 \xdef\rail@i@{#1}

 \rail@write{\string\rail@i{\number\rail@nr}{\rail@i@}}

 \endgroup

 \end

 }

 \newenvironment{rail}{

 \global\advance\rail@nr by 1

 \rail@first

 \rail@body

 }{

 \rail@matchtrue

 \@ifundefined{rail@o@\number\rail@nr}{\rail@matchfalse}{}

 \expandafter\ifx\csname rail@i@\number\rail@nr\endcsname\rail@i@

 \else

 \rail@matchfalse

 \fi

 \ifrail@match

 \csname rail@o@\number\rail@nr\endcsname

 \else

 \PackageWarning{rail}{Railroad diagram {\number\rail@nr} doesn't match}

 \global\let\rail@endwarn=\rail@warn

 \begin{list}{}{\rail@param}

 \rail@begin{1}{}

 \rail@setbox{\bfseries ???}

 \rail@oval

 \rail@end

 \end{list}

 \fi

 }

 \newcommand\railoptions[1]{

 \rail@first

 \rail@write{\string\rail@p{#1}}

 }

 \newcommand\railterm[1]{

 \rail@first

 \@for\rail@@:=#1\do{

 \rail@write{\string\rail@t{\rail@@}}

 }

 }

 \newcommand\railalias[2]{

 \expandafter\def\csname rail@t@#1\endcsname{#2}

 }

 \long\def\rail@i#1#2{

 \expandafter\gdef\csname rail@i@#1\endcsname{#2}

 }

 \def\rail@o#1#2{

 \expandafter\gdef\csname rail@o@#1\endcsname{

 \begin{list}{}{\rail@param}#2\end{list}

 }

 }

 \def\rail@t#1{}

 \def\rail@p#1{}

 \def\rail@write#1{\@ifundefined{tf@rai}{}{\immediate\write\tf@rai{#1}}}

 \def\rail@warn{

 \PackageWarningNoLine{rail}{Railroad diagram(s) may have changed.

                             Use 'rail' and rerun}

 }

 \let\rail@endwarn=\relax

 \AtEndDocument{\rail@endwarn}

 % index entry macro

 %

 % \rail@index{IDENT} : add index entry for IDENT

 \def\rail@index#1{

 \index{\rail@indexfont#1}

 }

 % railroad formatting primitives

 %

 % \rail@x : current x

 % \rail@y : current y

 % \rail@ex : current end x

 % \rail@sx : starting x for \rail@cr

 % \rail@rx : rightmost previous x for \rail@cr

 %

 % \rail@tmpa : temporary count

 % \rail@tmpb : temporary count

 % \rail@tmpc : temporary count

 %

 % \rail@put : put at (\rail@x,\rail@y)

 %

 % \rail@eline : end line by drawing from \rail@ex to \rail@x

 %

 % \rail@sety{LEVEL} : set \rail@y to level LEVEL

 \newcount\rail@x

 \newcount\rail@y

 \newcount\rail@ex

 \newcount\rail@sx

 \newcount\rail@rx

 \newcount\rail@tmpa

 \newcount\rail@tmpb

 \newcount\rail@tmpc

 \def\rail@put{\put(\number\rail@x,\number\rail@y)}

 \def\rail@eline{

 \rail@tmpb=\rail@x

 \advance\rail@tmpb by -\rail@ex

 \rail@put{\line(-1,0){\number\rail@tmpb}}

 }

 \def\rail@sety#1{

 \rail@y=#1

 \multiply\rail@y by -\rail@boxsp

 \advance\rail@y by -\rail@boxht

 }

 % \rail@begin{HEIGHT}{NAME} : begin a railroad diagram of height HEIGHT

 %

 % \rail@end : end a railroad diagram

 %

 % \rail@expand{IDENT} : expand IDENT

 \def\rail@begin#1#2{

 \item[]

 \begin{minipage}[t]{\linewidth}

 \ifx\@empty#2\else

 {\rail@namefont \rail@expand{#2}}\\*[\railnamesep]

 \fi

 \unitlength=\railunit

 \rail@tmpa=#1

 \multiply\rail@tmpa by \rail@boxsp

 \begin{picture}(0,\number\rail@tmpa)(0,-\number\rail@tmpa)

 \rail@ex=0

 \rail@rx=0

 \rail@x=\rail@extra

 \rail@sx=\rail@x

 \rail@sety{0}

 }

 \def\rail@end{

 \advance\rail@x by \rail@extra

 \rail@eline

 \end{picture}

 \end{minipage}

 }

 \def\rail@expand#1{\@ifundefined{rail@t@#1}{#1}{\csname rail@t@#1\endcsname}}

 % \rail@token{TEXT}[ANNOT] : format token TEXT with annotation

 %

 % \rail@ctoken{TEXT}[ANNOT] : format token TEXT centered with annotation

 %

 % \rail@nont{TEXT}[ANNOT] : format nonterminal TEXT with annotation

 %

 % \rail@cnont{TEXT}[ANNOT] : format nonterminal TEXT centered with annotation

 %

 % \rail@term{TEXT}[ANNOT] : format terminal TEXT with annotation

 %

 % \rail@cterm{TEXT}[ANNOT] : format terminal TEXT centered with annotation

 %

 % \rail@annote[TEXT] : format TEXT as annotation

 \def\rail@token#1[#2]{

 \rail@setbox{%

 {\rail@termfont \rail@expand{#1}}\ifx\@empty#2\else\ {\rail@annofont #2}\fi

 }

 \rail@oval

 }

 \def\rail@ctoken#1[#2]{

 \rail@setbox{%

 {\rail@termfont \rail@expand{#1}}\ifx\@empty#2\else\ {\rail@annofont #2}\fi

 }

 \rail@coval

 }

 \def\rail@nont#1[#2]{

 \rail@setbox{%

 {\rail@nontfont \rail@expand{#1}}\ifx\@empty#2\else\ {\rail@annofont #2}\fi

 }

 \rail@frame

 }

 \def\rail@cnont#1[#2]{

 \rail@setbox{%

 {\rail@nontfont \rail@expand{#1}}\ifx\@empty#2\else\ {\rail@annofont #2}\fi

 }

 \rail@cframe

 }

 \def\rail@term#1[#2]{

 \rail@setbox{%

 {\rail@termfont #1}\ifx\@empty#2\else\ {\rail@annofont #2}\fi

 }

 \rail@oval

 }

 \def\rail@cterm#1[#2]{

 \rail@setbox{%

 {\rail@termfont #1}\ifx\@empty#2\else\ {\rail@annofont #2}\fi

 }

 \rail@coval

 }

 \def\rail@annote[#1]{

 \rail@setbox{\rail@annofont #1}

 \rail@text

 }

 % \rail@box : temporary box for \rail@oval and \rail@frame

 %

 % \rail@setbox{TEXT} : set \rail@box to TEXT, set \rail@tmpa to width

 %

 % \rail@oval : format \rail@box of width \rail@tmpa inside an oval

 %

 % \rail@coval : same as \rail@oval, but centered between \rail@x and

 %               \rail@mx

 %

 % \rail@frame : format \rail@box of width \rail@tmpa inside a frame

 %

 % \rail@cframe : same as \rail@frame, but centered between \rail@x and

 %                \rail@mx

 %

 % \rail@text : format \rail@box of width \rail@tmpa above the line

 \newbox\rail@box

 \def\rail@setbox#1{

 \setbox\rail@box\hbox{\strut#1}

 \rail@tmpa=\wd\rail@box

 \divide\rail@tmpa by \railunit

 }

 \def\rail@oval{

 \advance\rail@x by \rail@boxlf

 \rail@eline

 \advance\rail@tmpa by \rail@ovalsp

 \ifnum\rail@tmpa<\rail@boxht\rail@tmpa=\rail@boxht\fi

 \rail@tmpb=\rail@tmpa

 \divide\rail@tmpb by 2

 \advance\rail@y by -\rail@boxhht

 \rail@put{\makebox(\number\rail@tmpa,\number\rail@boxht){\box\rail@box}}

 \advance\rail@y by \rail@boxhht

 \advance\rail@x by \rail@tmpb

 \rail@put{\oval(\number\rail@tmpa,\number\rail@boxht)}

 \advance\rail@x by \rail@tmpb

 \rail@ex=\rail@x

 \advance\rail@x by \rail@boxrt

 }

 \def\rail@coval{

 \rail@tmpb=\rail@tmpa

 \advance\rail@tmpb by \rail@ovalsp

 \ifnum\rail@tmpb<\rail@boxht\rail@tmpb=\rail@boxht\fi

 \advance\rail@tmpb by \rail@boxlf

 \advance\rail@tmpb by \rail@boxrt

 \rail@tmpc=\rail@mx

 \advance\rail@tmpc by -\rail@x

 \advance\rail@tmpc by -\rail@tmpb

 \divide\rail@tmpc by 2

 \ifnum\rail@tmpc>0

 \advance\rail@x by \rail@tmpc

 \fi

 \rail@oval

 }

 \def\rail@frame{

 \advance\rail@x by \rail@boxlf

 \rail@eline

 \advance\rail@tmpa by \rail@framesp

 \ifnum\rail@tmpa<\rail@boxht\rail@tmpa=\rail@boxht\fi

 \advance\rail@y by -\rail@boxhht

 \rail@put{\framebox(\number\rail@tmpa,\number\rail@boxht){\box\rail@box}}

 \advance\rail@y by \rail@boxhht

 \advance\rail@x by \rail@tmpa

 \rail@ex=\rail@x

 \advance\rail@x by \rail@boxrt

 }

 \def\rail@cframe{

 \rail@tmpb=\rail@tmpa

 \advance\rail@tmpb by \rail@framesp

 \ifnum\rail@tmpb<\rail@boxht\rail@tmpb=\rail@boxht\fi

 \advance\rail@tmpb by \rail@boxlf

 \advance\rail@tmpb by \rail@boxrt

 \rail@tmpc=\rail@mx

 \advance\rail@tmpc by -\rail@x

 \advance\rail@tmpc by -\rail@tmpb

 \divide\rail@tmpc by 2

 \ifnum\rail@tmpc>0

 \advance\rail@x by \rail@tmpc

 \fi

 \rail@frame

 }

 \def\rail@text{

 \advance\rail@x by \rail@textlf

 \advance\rail@y by \rail@textup

 \rail@put{\box\rail@box}

 \advance\rail@y by -\rail@textup

 \advance\rail@x by \rail@tmpa

 \advance\rail@x by \rail@textrt

 }

 % alternatives

 %

 % \rail@jx \rail@jy : current join point

 %

 % \rail@gx \rail@gy \rail@gex \rail@grx : global versions of \rail@x etc,

 %                                         to pass values over group closings

 %

 % \rail@mx : maximum x so far

 %

 % \rail@sy : starting \rail@y for alternatives

 %

 % \rail@jput : put at (\rail@jx,\rail@jy)

 %

 % \rail@joval[PART] : put \oval[PART] with adjust

 \newcount\rail@jx

 \newcount\rail@jy

 \newcount\rail@gx

 \newcount\rail@gy

 \newcount\rail@gex

 \newcount\rail@grx

 \newcount\rail@sy

 \newcount\rail@mx

 \def\rail@jput{

 \put(\number\rail@jx,\number\rail@jy)

 }

 \def\rail@joval[#1]{

 \advance\rail@jx by \rail@joinadj

 \rail@jput{\oval(\number\rail@joinsz,\number\rail@joinsz)[#1]}

 \advance\rail@jx by -\rail@joinadj

 }

 % \rail@barsplit : incoming split for '|'

 %

 % \rail@plussplit : incoming split for '+'

 %

 \def\rail@barsplit{

 \advance\rail@jy by -\rail@joinhsz

 \rail@joval[tr]

 \advance\rail@jx by \rail@joinhsz

 }

 \def\rail@plussplit{

 \advance\rail@jy by -\rail@joinhsz

 \advance\rail@jx by \rail@joinsz

 \rail@joval[tl]

 \advance\rail@jx by -\rail@joinhsz

 }

 % \rail@alt{SPLIT} : start alternatives with incoming split SPLIT

 %

 \def\rail@alt#1{

 \rail@sy=\rail@y

 \rail@jx=\rail@x

 \rail@jy=\rail@y

 \advance\rail@x by \rail@joinsz

 \rail@mx=0

 \let\rail@list=\@empty

 \let\rail@comma=\@empty

 \let\rail@split=#1

 \begingroup

 \rail@sx=\rail@x

 \rail@rx=0

 }

 % \rail@nextalt{FIX}{Y} : start next alternative at vertical position Y

 %                         and fix-up FIX

 %

 \def\rail@nextalt#1#2{

 \global\rail@gx=\rail@x

 \global\rail@gy=\rail@y

 \global\rail@gex=\rail@ex

 \global\rail@grx=\rail@rx

 \endgroup

 #1

 \ifnum\rail@gx>\rail@mx\rail@mx=\rail@gx\fi

 \ifnum\rail@grx>\rail@mx\rail@mx=\rail@grx\fi

 \edef\rail@list{\rail@list\rail@comma\number\rail@gex:\number\rail@gy}

 \def\rail@comma{,}

 \rail@split

 \let\rail@split=\@empty

 \rail@sety{#2}

 \rail@tmpa=\rail@jy

 \advance\rail@tmpa by -\rail@y

 \advance\rail@tmpa by -\rail@joinhsz

 \rail@jput{\line(0,-1){\number\rail@tmpa}}

 \rail@jy=\rail@y

 \advance\rail@jy by \rail@joinhsz

 \advance\rail@jx by \rail@joinhsz

 \rail@joval[bl]

 \advance\rail@jx by -\rail@joinhsz

 \rail@ex=\rail@x

 \begingroup

 \rail@sx=\rail@x

 \rail@rx=0

 }

 % \rail@barjoin : outgoing join for first '|' alternative

 %

 % \rail@plusjoin : outgoing join for first '+' alternative

 %

 % \rail@altjoin : join for subsequent alternative

 %

 \def\rail@barjoin{

 \ifnum\rail@y<\rail@sy

 \global\rail@gex=\rail@jx

 \else

 \global\rail@gex=\rail@ex

 \fi

 \advance\rail@jy by -\rail@joinhsz

 \rail@joval[tl]

 \advance\rail@jx by -\rail@joinhsz

 \ifnum\rail@y<\rail@sy

 \rail@altjoin

 \fi

 }

 \def\rail@plusjoin{

 \global\rail@gex=\rail@ex

 \advance\rail@jy by -\rail@joinhsz

 \advance\rail@jx by -\rail@joinsz

 \rail@joval[tr]

 \advance\rail@jx by \rail@joinhsz

 }

 \def\rail@altjoin{

 \rail@eline

 \rail@tmpa=\rail@jy

 \advance\rail@tmpa by -\rail@y

 \advance\rail@tmpa by -\rail@joinhsz

 \rail@jput{\line(0,-1){\number\rail@tmpa}}

 \rail@jy=\rail@y

 \advance\rail@jy by \rail@joinhsz

 \advance\rail@jx by -\rail@joinhsz

 \rail@joval[br]

 \advance\rail@jx by \rail@joinhsz

 }

 % \rail@eltsplit EX:Y; : split EX:Y into \rail@ex \rail@y

 %

 % \rail@endalt{JOIN} : end alternatives with outgoing join JOIN

 \def\rail@eltsplit#1:#2;{\rail@ex=#1\rail@y=#2}

 \def\rail@endalt#1{

 \global\rail@gx=\rail@x

 \global\rail@gy=\rail@y

 \global\rail@gex=\rail@ex

 \global\rail@grx=\rail@rx

 \endgroup

 \ifnum\rail@gx>\rail@mx\rail@mx=\rail@gx\fi

 \ifnum\rail@grx>\rail@mx\rail@mx=\rail@grx\fi

 \edef\rail@list{\rail@list\rail@comma\number\rail@gex:\number\rail@gy}

 \rail@x=\rail@mx

 \rail@jx=\rail@x

 \rail@jy=\rail@sy

 \advance\rail@jx by \rail@joinsz

 \let\rail@join=#1

 \@for\rail@elt:=\rail@list\do{

 \expandafter\rail@eltsplit\rail@elt;

 \rail@join

 \let\rail@join=\rail@altjoin

 }

 \rail@x=\rail@mx

 \rail@y=\rail@sy

 \rail@ex=\rail@gex

 \advance\rail@x by \rail@joinsz

 }

 % \rail@bar : start '|' alternatives

 %

 % \rail@nextbar : next '|' alternative

 %

 % \rail@endbar : end '|' alternatives

 %

 \def\rail@bar{

 \rail@alt\rail@barsplit

 }

 \def\rail@nextbar{

 \rail@nextalt\relax

 }

 \def\rail@endbar{

 \rail@endalt\rail@barjoin

 }

 % \rail@plus : start '+' alternatives

 %

 % \rail@nextplus: next '+' alternative

 %

 % \rail@endplus : end '+' alternatives

 %

 \def\rail@plus{

 \rail@alt\rail@plussplit

 }

 \def\rail@nextplus{

 \rail@nextalt\rail@fixplus

 }

 \def\rail@fixplus{

 \ifnum\rail@gy<\rail@sy

 \begingroup

 \rail@x=\rail@gx

 \rail@y=\rail@gy

 \rail@ex=\rail@gex

 \rail@rx=\rail@grx

 \ifnum\rail@x<\rail@rx

 \rail@x=\rail@rx

 \fi

 \rail@eline

 \rail@jx=\rail@x

 \rail@jy=\rail@y

 \advance\rail@jy by \rail@joinhsz

 \rail@joval[br]

 \advance\rail@jx by \rail@joinhsz

 \rail@tmpa=\rail@sy

 \advance\rail@tmpa by -\rail@joinhsz

 \advance\rail@tmpa by -\rail@jy

 \rail@jput{\line(0,1){\number\rail@tmpa}}

 \rail@jy=\rail@sy

 \advance\rail@jy by -\rail@joinhsz

 \advance\rail@jx by \rail@joinhsz

 \rail@joval[tl]

 \advance\rail@jy by \rail@joinhsz

 \global\rail@gx=\rail@jx

 \global\rail@gy=\rail@jy

 \global\rail@gex=\rail@gx

 \global\rail@grx=\rail@rx

 \endgroup

 \fi

 }

 \def\rail@endplus{

 \rail@endalt\rail@plusjoin

 }

 % \rail@cr{Y} : carriage return to vertical position Y

 \def\rail@cr#1{

 \rail@tmpa=\rail@sx

 \advance\rail@tmpa by \rail@joinsz

 \ifnum\rail@x<\rail@tmpa\rail@x=\rail@tmpa\fi

 \rail@eline

 \rail@jx=\rail@x

 \rail@jy=\rail@y

 \advance\rail@x by \rail@joinsz

 \ifnum\rail@x>\rail@rx\rail@rx=\rail@x\fi

 \advance\rail@jy by -\rail@joinhsz

 \rail@joval[tr]

 \advance\rail@jx by \rail@joinhsz

 \rail@sety{#1}

 \rail@tmpa=\rail@jy

 \advance\rail@tmpa by -\rail@y

 \advance\rail@tmpa by -\rail@boxsp

 \advance\rail@tmpa by -\rail@joinhsz

 \rail@jput{\line(0,-1){\number\rail@tmpa}}

 \rail@jy=\rail@y

 \advance\rail@jy by \rail@boxsp

 \advance\rail@jy by \rail@joinhsz

 \advance\rail@jx by -\rail@joinhsz

 \rail@joval[br]

 \advance\rail@jy by -\rail@joinhsz

 \rail@tmpa=\rail@jx

 \advance\rail@tmpa by -\rail@sx

 \advance\rail@tmpa by -\rail@joinhsz

 \rail@jput{\line(-1,0){\number\rail@tmpa}}

 \rail@jx=\rail@sx

 \advance\rail@jx by \rail@joinhsz

 \advance\rail@jy by -\rail@joinhsz

 \rail@joval[tl]

 \advance\rail@jx by -\rail@joinhsz

 \rail@tmpa=\rail@boxsp

 \advance\rail@tmpa by -\rail@joinsz

 \rail@jput{\line(0,-1){\number\rail@tmpa}}

 \advance\rail@jy by -\rail@tmpa

 \advance\rail@jx by \rail@joinhsz

 \rail@joval[bl]

 \rail@x=\rail@jx

 \rail@ex=\rail@x

 }