%D \module
%D   [       file=lang-frq,
%D        version=2004.01.15,
%D          title=\CONTEXT\ Language Macros,
%D       subtitle=Language Frequency Table Support,
%D         author=Hans Hagen,
%D           date=\currentdate,
%D      copyright={PRAGMA / Hans Hagen \& Ton Otten}]
%C
%C This module is part of the \CONTEXT\ macro||package and is
%C therefore copyrighted by \PRAGMA. See mreadme.pdf for
%C details.

\writestatus{loading}{Language Frequency Table Support}

\unprotect

\ifx\s!en\undefined \def\v!en{en}   \fi
\ifx\??lg\undefined \def\??lg{@@lg} \fi

%M \usemodule[layout]

%D \macros
%D   {charwidthmethod}
%D
%D This module implements a method for determining the width of an
%D average character in a language. It uses the dimensions of the
%D current fonts.
%D
%D \def\ShwChrWd#1#2#3%
%D   {\chardef\charwidthmethod#1\relax
%D    \mainlanguage[#2#3]\the\dimexpr(\averagecharwidth)}
%D
%D \starttabulate[|c|c|c|c|c|c|]
%D \HL
%D \NC      \NC\bf0=amount\NC\bf1=.5em\NC2=ex\NC\bf3=frequency\NC\bf4=list\NC\NR
%D \HL
%D \NC\bf en\NC\ShwChrWd0en\NC\ShwChrWd1en\NC\ShwChrWd2en\NC\ShwChrWd3en\NC\ShwChrWd4en\NC\NR
%D \NC\bf nl\NC\ShwChrWd0nl\NC\ShwChrWd1nl\NC\ShwChrWd2nl\NC\ShwChrWd3nl\NC\ShwChrWd4nl\NC\NR
%D \NC\bf de\NC\ShwChrWd0de\NC\ShwChrWd1de\NC\ShwChrWd2de\NC\ShwChrWd3de\NC\ShwChrWd4de\NC\NR
%D \HL
%D \stoptabulate
%D
%D Method~1 ignores the widths and assumes that each character has a
%D width of .5em, which is true for most monospaced fonts. Method~2
%D takes the x as starting point, and assumes that it's height kind of
%D matches its width. Method~3 is the best one, and determines the
%D average width based on the language specific character table.
%D Method~4 is a mixture between the first two methods: character
%D specific widths applied to an equal distribution. Method~0 reports
%D the total count, which normally is~100.

\chardef\charwidthmethod=3 % 0=amount 1=em 2=ex 3=frequency 4=flattened >4=ex

%D \macros
%D  {charwidthlanguage}
%D
%D The language used for the calculations is defined as:

\def\charwidthlanguage{\currentmainlanguage}

%D \macros
%D   {charfreq}
%D
%D This method comes into action in the following macro:

\def\charfreq#1 #2 % character fraction
  {+(\ifcase\charwidthmethod
     #2\dimexpr100\onepoint\relax
   \or
     #2\dimexpr.5em\relax % \emwidth/2
   \or
     #2\dimexpr\exheight\relax
   \or
     #2\fontcharwd\font`#1%
   \or
     \dimexpr100\fontcharwd\font`#1/\charactertsize\charwidthlanguage\relax % ugly hack
   \else
     #2\dimexpr\exheight\relax
   \fi)}

%D \macros
%D   {startcharactertable}
%D
%D A frequency table is defined with the following macro. The \type
%D {charfreq} macro is used in this table.

\def\startcharactertable[#1]#2\stopcharactertable % \dimexpr has fuzzy lookahead
  {\startnointerference
     \long\setgvalue{\??lg:w:#1}{#2}% the width vector
     \scratchcounter\zerocount \def\charfreq##1 ##2 {\advance\scratchcounter\plusone} #2%
     \long\setxvalue{\??lg:c:#1}{\the\scratchcounter}% the character count
   \stopnointerference}

%D \macros
%D   {charactertable,charactertsize}
%D
%D The table content as well as the number of entries can be fetched with
%D the following two macros. The architecture of the table and calling
%D macro permits a fully expandable application.

\def\charactertable#1%
  {\csname\??lg:w:\ifcsname\??lg:w:#1\endcsname#1\else\s!en\fi\endcsname}

\def\charactertsize#1%
  {\csname\??lg:c:\ifcsname\??lg:c:#1\endcsname#1\else\s!en\fi\endcsname}

%D Although it is of hardly any use, you can inherit a character table:
%D
%D \starttyping
%D \startcharactertable[cz] \charactertable{en} \stopcharactertable
%D \stoptyping
%D
%D We define a default vector with 100\% x's.

\startcharactertable[en] 100 x \stopcharactertable % kind of default

%D \macros
%D   {averagecharwidth}
%D
%D This macro reports the average width for the current main
%D language (\the \dimexpr (\averagecharwidth)).

\beginTEX

  \def\averagecharwidth{\the\emwidth}

\endTEX

\beginETEX \dimexpr

  \def\averagecharwidth{\dimexpr((\zeropoint\charactertable\charwidthlanguage)/100)}

\endETEX

\def\showcharfreq
  {\hbox\bgroup
     \charwidthlanguage:%
     \dostepwiserecurse041%
       {\chardef\charwidthmethod\recurselevel\relax
        \enspace\recurselevel/\the\dimexpr(\averagecharwidth)}%
   \egroup}

%D Just for fun, we show a few frequency tables as graphic (\in {figure}
%D [fig:charfreq]).
%D
%D \startbuffer
%D \definepalet [charfreq] [en=darkred, nl=darkgreen, de=darkblue]
%D
%D \def\charfreq#1 #2 %
%D   {\startMPdrawing
%D      interim linejoin := butt ;
%D      a := ASCII "#1" ;
%D      if (a >= (ASCII "a")) and (a <= (ASCII "z")) :
%D         draw ((0,#2*.25cm)--origin--(0,#2*.5cm))
%D           shifted (a*4mm+o,0)
%D           withpen pencircle scaled .5mm
%D           withcolor c;
%D      fi ;
%D    \stopMPdrawing}
%D
%D \resetMPdrawing
%D \startMPdrawing
%D   numeric a, o ; a := o := 0 ;
%D   color c ; c := .5white ;
%D   string s ; s := "" ;
%D \stopMPdrawing
%D
%D \startMPdrawing o := 0mm ; c := \MPcolor{charfreq:en} ; \stopMPdrawing
%D \charactertable{en}
%D
%D \startMPdrawing o := 1mm ; c := \MPcolor{charfreq:nl} ; \stopMPdrawing
%D \charactertable{nl}
%D
%D \startMPdrawing o := 2mm ; c := \MPcolor{charfreq:de} ; \stopMPdrawing
%D \charactertable{de}
%D
%D \startMPdrawing
%D   for a := ASCII "a" upto ASCII "z" :
%D     draw textext.bot("\strut\tttf " & char a) shifted (a*4mm+1mm,-1mm) ;
%D   endfor ;
%D \stopMPdrawing
%D
%D \MPdrawingdonetrue \getMPdrawing \resetMPdrawing
%D \stopbuffer
%D
%D \placefigure
%D   [here]
%D   [fig:charfreq]
%D   {The character distributions for English, Dutch and German.}
%D   {\getbuffer}
%D
%D A few samples of usage of this mechanism are shown below:
%D
%D \startbuffer
%D {\mainlanguage[en]\hsize65\averagecharwidth\mainlanguage[en]\input ward \blank}
%D {\mainlanguage[nl]\hsize65\averagecharwidth\mainlanguage[en]\input ward \blank}
%D {\mainlanguage[de]\hsize65\averagecharwidth\mainlanguage[en]\input ward \blank}
%D \stopbuffer
%D
%D \typebuffer \getbuffer
%D
%D Although the widthts differ, the consequenes for breaking the paragraph
%D into lines are minimal.

%D \macros
%D   {freezeaveragecharacterwidth}
%D
%D This macro can be used to make sure that the width does not change during a
%D page break when another font is used.

\let\normalaveragecharacterwidth\averagecharacterwidth

\def\freezeaveragecharacterwidth % global
  {\xdef\averagecharacterwidth{\dimexpr(\the\normalaveragecharacterwidth)}}

\protect \endinput
