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%D \module
%D [ file=t-bnf,
%D version=2004.6.23,
%D title=\CONTEXT\ BNF Grammar Module,
%D subtitle=Grammars,
%D author={Nikolai Weibull},
%D date=\currentdate,
%D copyright={Nikolai Weibull}]
%C
%C This module is NOT part of the \CONTEXT\ macro||package.
%C This module is free software; you can redistribute it and/or modify
%C it under the terms of the GNU General Public License as published by
%C the Free Software Foundation; either version 2 of the License, or
%C (at your option) any later version.
%C
%C This module is distributed in the hope that it will be useful,
%C but WITHOUT ANY WARRANTY; without even the implied warranty of
%C MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
%C GNU General Public License for more details.
%C
%C You should have received a copy of the GNU General Public License
%C along with this program; if not, write to the Free Software
%C Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
\writestatus{loading}{BNF Macros / Initialization}
\unprotect
%M \usemodule[bnf]
%D We define a new system variable for our settings:
\definesystemvariable{bnf}
%D We need some constants for the multi||lingual interface,
\startconstants english dutch
terminalstart: terminalstart terminalstart
terminalstop: terminalstop terminalstop
nonterminalstart: nonterminalstart nonterminalstart
nonterminalstop: nonterminalstop nonterminalstop
is: is worden
\stopconstants
%D and while we're at it, lets define some variables.
\startvariables english dutch
bnfgrammar: bnfgrammar bnfspraakleer
bnfgrammars: bnfgrammars bnfspraakleer
\stopvariables
%D Finally, we want the commands to be multi||lingually accessible, so we set
%D that up as well:
\startcommands english dutch
setupbnfgrammar: setupbnfgrammar stelbnfspraakleer
startbnfgrammar: startbnfgrammar startbnfspraakleer
stopbnfgrammar: stopbnfgrammar startbnfspraakleer
\stopcommands
%D \macros
%D {startbnfgrammar, stopbnfgrammar}
%D
%D Now to the interesting parts, those that are actually useful to the outside
%D world. First we have the \type{\startbnfgrammar} and \type{\stopbnfgrammar}
%D pairs, which are of course used to delimit \BNF\ grammars. We would like to
%D define \type{\startbnfgrammar} as \type{\def\startbnfgrammar[#1]}, but a bug
%D in \CONTEXT\ prevents us from doing this, as the first character in the
%D grammar may be active, for example \type{<}, but while checking for the
%D presence of \type{[}, it gets ruined. A way around it is of course to
%D require that the user pass an empty \type{[]} pair, and we will use this
%D method at the moment.
\def\complexstartbnfgrammar[#1]%
{\endgraf\nobreak\medskip
\begingroup
\setupbnfgrammar[#1]%
\chardef\bnfsinglequote=`'
\defineactivecharacter : {\@@bnfis}
\defineactivecharacter | {\@@bnfoption}
\defineactivecharacter " %
{\thinspace\bgroup\@@bnfterminalstart\setupinlineverbatim%
\defineactivecharacter " {\@@bnfterminalstop\egroup\thinspace}}
\defineactivecharacter ' %
{\thinspace\bgroup\@@bnfterminalstart\setupinlineverbatim%
\defineactivecharacter ' {\@@bnfterminalstop\egroup\thinspace}}
\catcode`<=13
\let\par=\bnfgrammarline
\obeylines}
\def\stopbnfgrammar{\medbreak\checknextindentation[\@@bnfindentnext]}
\definecomplexorsimpleempty\startbnfgrammar
%D \macros
%D {<>,bnfgrammarrule}
%D
%D We need a couple more macros to deal with the interior of a \BNF\ grammar.
%D \type{\<>} is used for non||terminals, and \type{\bnfgrammarrule} is used
%D later on in \type{\bnfgrammarswitch} for continuing a line.
\def\<#1>{\leavevmode\hbox{\@@bnfnonterminalstart#1\/\@@bnfnonterminalstop}}
\bgroup
\catcode`<=13
\global\let<=\<
\gdef\bnfgrammarrule<#1>{\endgraf\indent\<#1>}
\egroup
%D \macros
%D {bnfgrammarline, bnfgrammarswitch, bnfgrammarcont}
%D
%D These macros deal with the ending of a line in a grammar.
%D \type{\bnfgrammarline} is called whenever a new line begins, and invokes
%D \type{\bnfgrammarswitch} to determine what to do next. If the next token is
%D \type{\<}, we will call upon \type{\bnfgrammarrule} to deal with the new
%D rule. If it is \type{\stopbnfgrammar}, we end the top||level group, and let
%D it process \type{\stopbnfgrammar} afterwards. Otherwise we invoke
%D \type{\bnfgrammarcont}, which will end the line and add some indentation to
%D the continuing line.
\def\bnfgrammarline{\futurelet\next\bnfgrammarswitch}
\def\bnfgrammarswitch%
{\ifx\next\<
\let\next=\bnfgrammarrule
\else\ifx\next\stopbnfgrammar
\let\next=\endgroup
\else
\let\next=\bnfgrammarcont
\fi\fi
\next}
\def\bnfgrammarcont{\hfil\break\indent\qquad}
%D \macros
%D {setupbnfgrammar}
%D
%D We want to allow our users to change the way the \BNF\ grammars are typeset,
%D so we define a setup command for them to use.
%D
%D It allows you to define the start and stop sequence for terminals and
%D non||terminals, as well as colons (lhs / rhs separator) and vertical bars
%D (alternative), and commas. This has been multi||lingualized above, so
%D choose your language.
\def\dosetupbnfgrammar[#1]%
{\getparameters[\??bnf][#1]}
\def\setupbnfgrammar%
{\dosingleargument\dosetupbnfgrammar}
\setupbnfgrammar
[\c!terminalstart=\tttf,
\c!terminalstop=,
\c!nonterminalstart=\mathematics{\langle},
\c!nonterminalstop=\mathematics{\rangle},
\c!is={ \mathematics{\longrightarrow}},
\c!option=\mathematics{\vert},
\c!indentnext=\v!no]
%D \macros
%D {BNF}
%D
%D We also define a useful abbreviation to be used for header texts and labels.
\logo[BNF]{bnf}
%D And we use it here:
\setupheadtext[\s!en][\v!bnfgrammar=\BNF\ Grammar]
\setupheadtext[\s!en][\v!bnfgrammars=\BNF\ Grammars]
\setuplabeltext[\s!en][\v!bnfgrammar=\BNF\ Grammar ]
%D Finally we define a float to be use with \BNF\ grammars, so that we can
%D finish off with something like this:
%D
%D \startbuffer
%D \placebnfgrammar
%D [][]
%D {An example of a placed grammar.}
%D {\startbnfgrammar[]
%D <exp>: <num> | <num> "+" <num>
%D <num>: "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9"
%D \stopbnfgrammar}
%D \stopbuffer
%D
%D \typebuffer
%D
%D \getbuffer
%D
%D which looks kind of nice.
\definefloat
[\v!bnfgrammar]
[\v!bnfgrammars]
\protect \endinput
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