ConTeXt and Lua programming/ConTeXt Lua Documents CLD
ConTeXt Lua Documents (CLD) are way to access TeX from inside Lua scripts; they provide means to typeset documents using little to no TeX code at all. This makes them especially helpful for automated content generation and scripting. Internally, the Lua commands are mapped onto their ConTeXt and TeX counterparts. Knowledge of the latter is, therefore, a prerequisite to writing CLDs. If you ever dreamed of proper typesetting without backslashes galore, here is where to start at.
Contents
Basic reading
- The CLD manual by Hans Hagen.
- cldf-ini.lua: the entry point for the cldf-* files that contain the CLD implementation.
An Example
Writing CLDs is straightforward although there are some pitfalls. Suppose we want to typeset the following minimal example:
\starttext \placefigure {none} {% \framed [frame=on, align=middle] {% \input knuth }% }% \stoptext
As CLD this will require more verbosity because nesting -- in the present example a framed
inside a placefigure
-- has to be expressed through functions.
Optional and key-value style arguments are expressed as arrays and dictionaries respectively, which is a transparent representation of their ConTeXt ancestors.
Mandatory (grouped) arguments are given either as strings or as functions.
Nesting 1: Functions
The following example shows two ways of rewriting the above TeX code: the first one closely resembles its structure while the second calls the function test
from inside the placefigure
macro.
context.placefigure( "none", function() context.framed( { frame="on", align="middle" }, function() context.input("knuth") end ) end ) context.par() function text () context.framed( { frame="on", align="middle" }, function() context.input("knuth") end ) end context.placefigure( "none", function () text() end )
Nesting 2: Delayed
An alternative to the function encapsulation is provided by the context.delayed.f() method. This way execution of the \input command is prevented until \placefigure is passed to TeX, the obvious advantage being that the source code follows the original TeX code and that it eliminates the need to create a separate function.
context.placefigure( "none", function() context.framed( { frame="on", align="middle" }, context.delayed.input("knuth") ) end )
Setting up Header Texts
As already shown in the section about Nesting 1: Functions also context.setupheadertexts needs to be called with functions. On top of this we need to know, that once context.setupheadertexts is executed it is not frozen. This makes it necessary, that we need to add "return true" inside each used function() call. This makes sure that the called function stays around until the run is finished.
A complete setup of header texts in a double-sided ConTeXt Lua Document could look then like this
context.setupheadertexts( {function() context.getmarking({"chapter"}) return true end }, {function() context.pagenumber() return true end }, {function() context.getmarking({"section"}) return true end }, {function() context.pagenumber() return true end })