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Add hints on bracket usage; c&p from the list: https://www.mail-archive.com/ntg-context@ntg.nl/msg87937.html
== Programming Techniques ==* [[Processing Lists]]: Processing lists of values* [[Counters]]: Manipulating counters in context* [[Expressions]]: Evaluating expressions of type number, dimen, glue or muglue* [[Commands with KeyVal arguments|Commands with Key=Value argumentsExecutesystemcommand]]: process contents of an environment by another program* Loops and expansion [http://randomdeterminism.wordpress.com/2009/03/05/tex-programming-the-past-the-present-and-the-future/ (blog post)]
== Debugging == * [[Commands Console Mode]]: Using ConTeXt on keyboard input directly, rather than loading a <tt>.tex</tt> file. = Use of brackets = One must '''not''' confuse with the LaTeX convention where "mandatory"arguments are contained in curly braces and brackets indicate"optional " arguments. Curly braces not only give grouping but generallyare used for objects to be typeset, as for \in{Figure}{a} [fig:ref]. For new users, it is worth repeating here that arguments within bracescan be either a comma-separated list of words OR a comma-separatedlist of keyword=value pairs, BUT NOT A MIXTURE OF BOTH. Generally, akeyword=value exists for all words, for example \cite[authoryear][ref]and \cite[alternative=authoryear,reference=ref] values can be grouped using curly braces, as in\cite[alternative=authoryear,lefttext={{see },}][ref1,ref2] where thelefttext is associated with the first cite reference (and none with thesecond). This can be tricky but is in fact rather straight-forward. = Using variables = There are several ways to handle variables in ConTeXt.The recommended and easiest method is to use the<tt>\setvariables</tt> and <tt>\getvariable</tt> macros.Doing it this way you also avoid to get in conflict withalready defined stuff (as variables use their own namespace). To store variables, you can use the <tt>\setvariables</tt>macro. <texcode>% stores value in variable namespace:key\setvariables[namespace][key=value]% stores the expanded value\setevariables[namespace][key=value]% global\setgvariables[namespace][key=value]% global and expanded value\setxvariables[namespace][key=value]</texcode> Use <tt>\getvariable</tt> to process a variable. Reading an undefinedvariable results in the <tt>\empty</tt> token. This is not a serious problem,as long as you expect text only.But be warned: the compilation process breaks, if you expect a dimensionor number. So better take care, that you define your variables, before you use them. <texcode>% gets value of the variable namespace:key\getvariable{namespace}{key}</texcode> To avoid problems, also pay attention to the following: You can set several variables (same namespace) at the same time.So the command <tt>\setvariables</tt> logically uses the '''plural''' formand works with '''square brackets'''.On the other hand you can only process one variable at the same time, so<tt>\getvariable</tt> uses the '''singular''' form and works with '''braces'''. OK, here comes a simple example. Let's say, that we want to have variablespace before and after a letter macro called <tt>\Opening</tt>. <texcode>\long\def\Opening#1{% \getvariable{Letter:opening}{before} \noindent{\begstrut#1\endstrut} \getvariable{Letter:opening}{after}}</texcode> By using variables in your macros, you can separate the layout definition,so that your macros get much more flexible.Just ensure, that all variables are set, before you use them! In this example we want to have a blank line in front of the opening, andtwo blank lines right after it. The value for the second key containssquare brackets, so it must be enclosed in braces. <texcode>\setvariables[Letter:opening] [before=\blank, after={\blank[2*big]}, ]</texcode> You can now save this style setup (among others) in a separate file andinclude it at the start of your document (before <tt>\Opening</tt> isdefined or at least used). And don't forget:'''Ensure that all variables are set before you use them!''' == CLD ==How to pass variable from TeX to Lua and vice versa? See [[CLD_passing_variables#Variables|CLD passing variables]]. = Defining new commands = == Special characters in command names == Some commands have special characters in their names, that TeX normally does not consider to be letters: <tt>@</tt>, <tt>!</tt> and <tt>?</tt>. Before and after the use or definition of such protected commands in your input files, the catcode of these characters has to be changed.This is done by {{cmd|unprotect}} and {{cmd|protect}}: <texcode>\unprotect\def\!test{alfa} \protect </texcode> The newly defined command <tt>\!test</tt> can of course only be called upon when we are in the {{cmd|unprotect}}ed state, otherwise TeX reads the command <tt>\!</tt>, followed by the word <tt>test</tt> (and probably complains loudly about not being in math mode). These protection/unprotection commands can be nested. When the nesting becomes deeper than one level, the system reports the current protection level. It is a good habit to always start your macro files with {{cmd|unprotect}} and end them with {{cmd|protect}}. = Passing verbatim text as macro parameter = (For passing text to LuaTex verbatim, see the [[Programming_in_LuaTeX#Manipulating_verbatim_text_for_dummies|Programming in LuaTeX]] article on this wiki.) In case you want to write macros that should handle verbatim text,you can use the tex primitives <tt>\obeyspaces</tt> and <tt>\obeylines</tt>.<tt>\obeyspaces</tt> changes the category code of the space character,so that spaces become significant. <tt>\obeylines</tt> does the same for thenewline character. This works fine for the following example: <texcode>\framed{\obeyspaces{A gap from here to there!}}</texcode> <context>\framed{\obeyspaces{A gap from here to there!}}</context> But if you pass this text as a parameter for your own macro<tt>\TextWithSpaces</tt> <texcode>\def\TextWithSpaces#1{\framed{\obeyspaces#1}}%\TextWithSpaces{A gap from here to there!}</texcode> <context>\def\TextWithSpaces#1{\framed{\obeyspaces#1}}%\TextWithSpaces{A gap from here to there!}</context> the additional spaces are '''ignored'''.This happens because the category code change is not yet in effect whenthe argument is parsed, and the spaces are removed during parsing. To keepthe spaces, the catcode change must be done '''before''' the argument is parsed. Here is a two-part solution for the problem (''suggested by Taco Hoekwater''): <texcode>\def\TextWithSpaces{\bgroup\obeyspaces\doTextWithSpaces}\def\doTextWithSpaces#1{\framed{#1}\egroup}</texcode> Another way is to postpone argument loading (''suggested by Hans Hagen''). <texcode>\def \TextWithSpaces {\framed\bgroup\obeyspaces\doTextWithSpaces}\def\doTextWithSpaces #1{#1\egroup} </texcode> Both of these produce the desired result: <context>\def \TextWithSpaces {\framed\bgroup\obeyspaces\doTextWithSpaces}\def\doTextWithSpaces #1{#1\egroup} \TextWithSpaces{A gap from here to there!}</context> [[Category:Programming and Databases]][[Category:Tools]]