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{{note | This is a wikified version of [https://www.tug.org/members/TUGboat/tb30-2/tb95mahajan-luatex.pdf this TugBoat article ]. Feel free to modify it. }}= Calling Lua from TeX =
In this article, I explain how to use The interweaving of ConTeXt and Lua to write macros in [[LuaTeX]]. I give some examples consists of macros two elements: first you tell TeX that are complicated in [[PdfTeX]]you're starting some Lua code; then, but can be defined easily using once inside Lua in LuaTeX. These examples include macros that do arithmetic on their arguments, you need to use loops, parse their arguments, and manipulate verbatim textthe appropriate functions to put things into the TeX stream.
= Introduction =There are two main ways to execute Lua code in a ConTeXt document: The command <code>\ctxlua</code>, and the environment <code>\startluacode...\stopluacode</code>. Both are wrappers around the LuaTeX primitive <code>\directlua</code>, which you should never need to use. In general, you will define a function inside a <code>\startluacode</code> block, and then define a TeX command that calls the function using <code>\ctxlua</code>, especially because <code>\ctxlua</code> has a few idiosyncracies.
As its name suggests, [[LuaTeX]] adds The main thing about Lua, code in a programming language, to TeX, document is this: the typesettercode is expanded by TeX ''before'' Lua gets to it. '''This allows us to program TeX in a high-level programming language. For example, consider a TeX macro means that divides two numbers. Such a macro is provided by all the <tt>fp</tt> package and also by <tt>pgfmath</tt> library of Lua code, even the <tt>TikZ</tt> package. The following comment is from the <tt>fp</tt> package<texcode>\def\FP@div#1#2.#3.#4\relax#5.#6.#7\relax{% % [...] algorithmic idea (for x>0comments, y>0) % - %determine \FP@shift such that % y*10^\FP@shift < 100000000 % <=y*10^(\FP@shift+1) % - %determine \FP@shiftmust be valid TeX!' such that % x*10^\FP@shift'< 100000000 % <=x*10^(\FP@shift+1) % - x=x*\FP@shift' % - y=y*A string like "\FP@shift % - \FP@shift=\FP@shift-\FP@shift' % - res=0undefined" will cause an immediate failure. % - while y>0 %fixed-point representation! % - \FP@times=0 % - while x>y % - \FP@times=Calling a bit of Lua inline: \FP@times+1 % - xctxlua =x-y % - end % - y=y/10 % - res=10*res+\FP@times/1000000000 % - end % - %shift the result according to The command <code>\FP@shiftctxlua</texcodecode>is for short inline snippets of Lua, suchas
The <tt>pgfmath</tt> library implements the macro in a similar way, but limits the number of shifts that it does. These macros highlight the state of affairs in writing TeX macros. Even simple things like multiplying two numbers are hard; you either have to work extremely hard to circumvent the programming limitations of TeX, or, more frequently, hope that someone else has done the hard work for you. In LuaTeX, such a function can be written using the <code>/</code> operator (I will explain the details later):
Thus<code>\ctxlua</code> operates under the normal TeX catcodes (category codes). This means the following two things for the Lua code inside:* all newlines get treated as spaces* special TeX characters like &, #, $, with LuaTeX ordinary users can write simple macros; and{, perhaps more importantly}, can read and understand macros written by TeX wizardsetc., need to be escaped.
Since the LuaTeX project started it has been actively supported by ConTeXt. <ref>Not surprisingIn addition, as two of LuaTeX main developers—Taco Hoekwater and Hans Hagen—are also the main ConTeXt developers.</ref> These days, the various <em>How do I write such a macro</em> questions on the ConTeXt mailing list are answered by a solution that uses Lua. I present a few such examples in this article. I have deliberately avoided examples about [[Fonts in LuaTeX | fonts]] and non-Latin languages. There is already quite a bit of documentation about them. In this article, I highlight how to use LuaTeX to write macros that require some <em>flow control</em>: randomized outputs, loops, and parsingwarning above still holds. = Interaction between TeX and Lua = To a first approximation, All the interaction between TeX and Lua is straightforward. When TeX (i.e., the LuaTeX engine) starts, it loads the input file in memory and processes it token by token. When TeX encounters <code>\directlua</code>, it stops reading the file in memory, <em>fully expands the argument of <code>\directlua</code></em>, and passes even the control to a Lua instance. The Lua instance, which runs with a few preloaded librariescomments, processes the expanded arguments of <code>\directlua</code>. This Lua instance has a special output stream which can must be accessed using <code>tex.print(...)</code>. The function <code>tex.print(...)</code> is just like the Lua function <code>print(...)</code> except that <code>tex.print(...)</code> prints to a <em>TeX stream</em> rather than to the standard output. When the Lua instance finishes processing its input, it passes the contents of the <em>TeX stream</em> back to TeX.<ref>The output of <code>tex.print(...)</code> is buffered and not passed to TeX until the Lua instance has stopped.</ref> valid TeX then inserts the contents of the <em>TeX stream</em> at the current location of the file that it was reading; expands the contents of the <em>TeX stream</em>; and continues. If TeX encounters another <code>\directlua</code>, the above process is repeated. As an exercise, imagine what happens when the following input is processed by LuaTeX. <ref>In this example, I used two different kinds of quotations to avoid escaping quotes. Escaping quotes inside <code>\directlua</code> is tricky. The above was a contrived example; if you ever need to escape quotes, you can use the <code>\startluacode ... \stopluacode</code> syntax explained later.</ref>
<texcode>\directlua% {tex.print("Depth 1 \\directlua{tex.print('Depth 2')}")}</texcode> On top of these LuaTeX primitives, ConTeXt provides a higher level interface. There are two ways to call Lua from ConTeXt. The first is a macro <Some code>\ctxlua</code> (read as ConTeXt Lua), which is similar to <code>\directlua</code>. (Asideillustrate the newline problem: It is possible to run the Lua instance under different name spaces. <code>\ctxlua</code> is the default name space; other name spaces are explained later.) <code>\ctxlua</code> is good for calling small snippets of Lua. The argument of <code>\ctxlua</code> is parsed under normal TeX catcodes (category codes), so the end of line character has the same catcode as a space. This can lead to surprises. For example, if you try to use a Lua comment, everything after the comment gets ignored.
This can be avoided by using a TeX comment instead of a Lua comment. However, working under normal TeX catcodes poses a bigger The problem: with special TeX characters like &, #, $, {, }, etc., need to be escaped. For example, # has to be escaped with (<code>\string#t</code> to be used in is Lua for 'the length of array <code>\ctxluat</code>.)
As == A larger Lua block: \startluacode...\stopluacode == Inside the argument of <code>\ctxluastartluacode...\stopluacode</code> is fully expandedenvironment, escaping newlines and special characters can sometimes be trickybehave normally. To circumvent this This solves the catcode problemthat <code>\ctxlua</code> suffers from. Apart from these special characters, ConTeXt defines a environment called the main warning remains in force: all the Lua code, even the comments, must be valid TeX. <codetexcode>\startluacode -- The unknown command \undefined will cause this entire block to fail. -- Print a countdown '10, 8, ..., 0!' -- `..` is Lua for string concatenation for i = 10, 2, -2 do context(i .. ", ") end context("0!") -- \\par is equivalent to a blank line in the input -- (Notice the escaped backslash: TeX won't mind the above comment.) context.par() -- Look! we can use # and $ with impunity! context("Unless we print them, then we must \\#\\$\\& print the escape characters, too. ")\stopluacode</texcode> == Putting Lua code in an external file == You can put your lua code in an external file (with the <code>. This sets lua</code> extension) and include it with the catcodes to what one would expect in Lua. Basically only <code>\require</code> has its usual TeX meaning, command: <texcode>\startluacode-- include the catcode of everything else file my-lua-lib.luarequire("my-lua-lib")\endluacode</texcode> == Namespaces == It is set a good habit to otherput your custom-defined functions in their own namespace. So, The traditional namespace for all practical purposes, we can forget about catcodes inside this is <code>\startluacode ... \stopluacodeuserdata</code>. The above two examples can be written as:
-- A Lua comment tex.print("This is printed.")if userdata doesn't exist yet, create it local t userdata = userdata or {1,2,3,4} tex -- define a shorter synonym u = userdata -- create my custom function inside the userdata namespace function u.printmyfunction("length " .. #t) -- do stuff end
name = "Jane"date = "today"context("Hello %s, how are you %s?", name, date)-- \undefinedBecomes 'Hello Jane, how are you today?'
will give an error because when TeX expands the contents, it encounters <code>\undefined</code> which is an undefined TeX macro. This error can be avoided by using <code>\type{\undefined}</code> or <code>\\undefined</code>. In general, the <code>\startluacode</code> ... <code>\stopluacode</code> environment is meant for moderately sized code snippets. For longer Lua code, it is more convenient to write the code in a separate Lua file and then load it using Lua's <code>dofile(...)</code> function.
ConTeXt also provides More primitively, you have <code>tex.print()</code> and <code>tex.sprint()</code>. Either one can take as an argument either a Lua function to conveniently write to number of strings, or an array of strings, and will then insert the strings into the TeX stream. The function only difference is called that <code>contexttex.print(...)</code> and it is equivalent to treats each string as a separate input line, while <code>tex.print(string.formatsprint(...))</code>doesn't. So the following lines
Using the above, it is easy to define TeX macros that pass control to Lua, do some processing in Lua, and then pass the result back to TeX. For example, a macro to convert a decimal number to hexadecimal can be written simply, by asking Lua to do the conversion.
\def\TOHEX#1{\ctxlua{contexttex.print("\%Xa",#1"b")}}\TOHEXctxlua{35tex.print({"a", "b"})}
The percent sign had to be escaped because are both interpreted by TeX as <texcode>ab</texcode> but when we use <code>tex.sprint</code>instead, either of the following <texcode>\ctxlua{tex.sprint("a", "b")}\ctxlua{tex.sprint({"a", "b"})}</codetexcode> assumes will be read by TeX catcodesas <texcode>ab</texcode> without any space in between. Sometimes, escaping arguments can be difficult; instead == Context commands == Most commands that you would type with a backslash in plain ConTeXt, it you can be easier to define a access from Lua function inside with <code>\startluacode context... \stopluacode</codeem> and call it using command<code/em>\ctxlua</code>. For example, a macro that takes a comma separated list of Unadorned strings and prints a random item can be written end up in TeX as arguments in curly braces; Lua tables end up in TeX as paramater blocks in square brackets. The following two pieces of code are equivalent:
userdata = userdata or context.chapter({first}, "Some title") math context.randomseedstartcolumns( os{n = 3, rule = "on"}) context("Hello one") context.timecolumn() context("Hello two") function userdata context.randomcolumn(...) context("Hello three") context(arg[math.randomstopcolumns(1, #arg)]) end
\def\CHOOSERANDOM#1% {\ctxlua{userdata.random(#1)}}</texcode>
I could have written For a wrapper so that fuller account of the function takes a list of words and chooses a random word among themcontext. For an example of such a conversioncommands, see the <em>sorting a list of tokens</em> page on the [http://Luatexwww.bluwikipragma-ade.com/gogeneral/Sort_a_token_list LuaTeX wikimanuals/cld-mkiv.pdf ConTeXt Lua document]manual. It is old, but most of it still applies.
In One final note: arguments can also be specified in the form of nested functions. Because LuaTeX evaluates the abovedeepest-nested argument first, I created a name space called <code>userdata</code> and defined this may cause the function <code>randomcontext()</code> calls to be evaluated in that name spacethe wrong order. Using a name space avoids clashes with For more on this, see the article on [[cld|ConTeXt Lua functions defined in LuaTeX documents]], and ConTeXtalso, again, the [http://www.pragma-ade.com/general/manuals/cld-mkiv.pdf CLD manual].
In order to avoid name clashes, = Passing arguments and buffers: ConTeXt also defines independent name spaces of commands that hook into Lua instances. They are =
Thus, for example, instead of <code>\ctxlua</code> and <code>\startluacode ... \stopluacode</code>, the <code>user</code> instance can be accessed via the macros <code>\usercode</code> and <code>\startusercode ... \stopusercode</code>. In instances other than <code>isolated</code>, all the Lua functions defined by ConTeXt (but not the inbuilt Lua functions) are stored in a <code>global</code> name space. In the <code>isolated</code> instance, all Lua functions defined by ConTeXt are hidden and cannot be accessed. Using these instances, we could write the above <code>\CHOOSERANDOM</code> macro as follows
Since I defined the function ''NB'': quoting with <code>[==[#1]==]</code>([http://www.lua.org/manual/5.2/manual.html#3.1 long strings])works just like <code>random"#1"</code> in most cases, but in addition it is robust against <code>#1</code> containing the quotation mark<code>user"</code> instance of which would terminate the Lua, I did not bother to use a separate name space for the functionstring prematurely. The Lua functions Inside <code>os\protect ..time\unprotect</code>, which is defined by a LuaTeX library, the macros <code>\!!bs</code>and <code>context\!!es</code>, which is defined by ConTeXt, needed are at your disposition.They are equivalent to be accessed through a <code>global[===[</code> name spaceand <code>]===]</code> and --being single tokens to TeX -- parsed faster. On the other hand, the (See [http://repo.or.cz/w/context.git/blob/refs/heads/origin:/tex/context/base/luat-ini.mkiv#l174 <code>mathluat-ini.randomseedmkiv</code> function, which is part of Lua, could be accessed as is]. )
A separate Lua instance also makes debugging slightly easier== Making \startenv... With <code>\ctxlua</code> stopenv hook into Lua ==The first job is, as ever, to have the Lua function at the error message starts withready
! LuaTeX error <main ctx instance>:\startluacode userdata = userdata or {} function userdata.verynarrow(buffer) -- equivalent to \startnarrower[10em] context.startnarrower({"10em"}) context(buffer) context.stopnarrower() end\stopluacode
With <code>\usercode</code> Next, we define the error message starts withstart command of our custom buffer:
! LuaTeX error <private user instance>\def\startverynarrow% {\dostartbuffer [verynarrow] % buffer name [startverynarrow] % command where buffer starts [stopverynarrow]} % command where buffer ends % also:command invoked when buffer stops
This makes Lastly, we define the <code>\stopverynarrow</code> command such that it easier passes the recently-complated buffer to narrow down the source of error. our <code>verynarrow</code> Lua function:
Normally, it is best to define your Lua functions in the <codetexcode>user</code> name space\def\stopverynarrow {\ctxlua {userdata.verynarrow(buffers. If you are writing a module, then define your Lua functions in the <code>thirdgetcontent('verynarrow'))}}</codetexcode> instance and in a name space which is the name And that's it! The rest of your module. In this article, I will simply use the default Lua instance, but take care to define all my Lua functions in a <code>userdata</code> name spaceconsist of examples. = Examples =
Now that we have some idea of how to work with LuaTeX, let's look at some examples.== Arithmetic without using an abacus ==
= Arithmetic without using an abacus =''This example demonstrates writing simple commands that invoke \ctxlua.''
= Loops without worrying about expansion =''This example demonstrates using Lua to write a quasi-repetitive piece of ConTeXt code.''
The tedious (but faster!) way to achieve this This is to simply type easy in LuaTeX. Once a Lua instance starts, TeX does not see anything until the whole table by handLua instance exits. It is however natural to want to So, we can write this table as a the loopin Lua, and compute simply print the valuesthat we would have typed to the TeX stream. When the control is passed to TeX, TeX sees the input as if we had typed it by hand. A first ConTeXt implementation using This is the Lua code for the recursion level might beabove table:
By contrast, in LuaTeX writing loops is easy. Once a Lua instance starts, TeX does not see anything until the Lua instance exits. So, we can write the loop in Lua, and simply print the values that we would have typed to the TeX stream. When the control is passed to TeX, TeX sees the input as if we had typed it by hand. Consequently, macro expansion is no longer an issue. For example, we can get the above table by:
<texcode>
The Lua functions such as <code>context.bTABLE()</code> and <code>context.bTR()</code> are just abbreviations for running <code>context ("\\bTABLE")</code>, <code>context("\\bTR")</code>, etc. See the [http://www.pragma-ade.com/general/manuals/cld-mkiv.pdf ConTeXt Lua document] manual for more details about such functions. The rest of the code is a simple nested for-loop that computes the sum of two dice. We do not need to worry about macro expansion at all!== Parsing input without exploding your head ==
= Parsing input without exploding your head =So, we need a function that can take a string like that, parse it, and turn it into the appropriate TeX code. LuaTeX includes a general parser based on PEG (parsing expression grammar) called [http://www.inf.puc-rio.br/~roberto/lpeg/lpeg.html lpeg], and it makes writing little parsers positively joyful. (Once you've got the knack of it, at least.) For example, the above <code>\molecule</code> macro can be written as follows.
In order to get around the weird rules of macro expansion, writing a parser in TeX involves a lot of macro jugglery and catcode trickery. It is a black art, one of the biggest mysteries of TeX for ordinary users.
As an example, let's consider typesetting chemical molecules in TeX. Normally, molecules should be typeset in text mode rather than math mode. For example, <context>H\low{2}SO\lohi{4}{--}</context>, can be input as <code>H\low{2}SO\lohi{4}{--}</code>. Typing so much markup can be cumbersome. Ideally, we want a macro such that we type <code>\molecule{H_2SO_4^-}</code> and the macro translates this into <code>H\low{2}SO\lohi{4}{--}</code>. Such a macro can be written in TeX as follows.
\def\chemhigh#1% -- we will put our molecule function in the userdata namespace. userdata = userdata or {\ifvoid\chemlowbox \high{{\switchtobodyfont[small]#1}}% \else \lohi{\box\chemlowbox} {{\switchtobodyfont[small]#1}} \fi}
\def\finishchem%-- The formatting functions into which the captured {\ifvoid\chemlowbox\else -- superscript/subscript blocks will be fed \lowlocal formatters = {\box\chemlowbox} \fi}
\unexpanded\def\molecule% {\bgroup \catcode`\_=\active \uccode`\~=`\_ \uppercase{\let~\chemlow}% \catcode`\^=\active \uccode`\~=`\^ \uppercase{\let~\chemhigh}% \dostepwiserecurse {65}{90}{1} {\catcode \recurselevel = \active function formatters.low(one) return string.format("\uccode`\~=\recurselevel \uppercaselow{\edef~{\noexpand\finishchem \rawcharacter{\recurselevel}}}}% \catcode`\-=\active \uccode`\~=`\- \uppercase{\def~{--}s}% ", one) \domolecule }% end
This monstrosity is a typical TeX parserfunction formatters. Appropriate characters need to be made active; occasionallylowhigh(one, <code>two) return string.format("\lccode</code> and <code>\uccode</code> need to be set; signaling tricks are needed (for instancelohi{%s}{%s}", one, checking if <code>\chemlowbox</code> is void); and then magic happens (or so it seems to a flabbergasted usertwo). More sophisticated parsers involve creating finite state automata, which look even more monstrous.end
With LuaTeX, things are differentfunction formatters. LuaTeX includes a general parser based on PEG highlow(parsing expression grammarone, two,three) called [http://www return string.inf.puc-rio.br/roberto/lpeg/lpeg.html lpeg]. This makes writing parsers in TeX much more comprehensible. For example, the above <code>format("\molecule</code> macro can be written as <texcode>\startluacodeuserdata = userdata or lohi{%s}{%s}", one,two)end
local lowercase = lpeg.R("az")-- These are the characters we may encounterlocal uppercase = lpeg-- The `/` means we want to expand + and - to \textplus c.R("AZ")local backslash = lpegq.P("\\")textminus;-- this substition is not instant, but will take place inside the first local csname = backslash * -- surrounding lpeg.PCs(1) * (1-backslash)^0call.local plus = lpeg.P("+") / "\\textplus "local minus = lpeg.P("-") / "\\textminus "local digit character = lpeg.R("az", "AZ", "09")-- R is for 'range'local sign = plus + minuslocal cardinal subscript = digit^1local integer = sign^0 * cardinallocal leftbrace = lpeg.P("{_") -- P is simply for 'pattern'local rightbrace superscript = lpeg.P("}^")local nobrace = 1 - (leftbrace + rightbrace)local nested = lpeg.P ("{leftbrace * (csname + sign + nobrace + lpeg.V(1)")^0 * rightbrace}local any rightbrace = lpeg.P(1"}")
local lowhigh = lpeg.Cc("\\lohi{%s}{%s}") * subscript * content * superscript * content / string.formatlocal highlow = lpeg.Cc("\\hilo{%s}{%s}") * superscript * content * subscript * content / string.formatlocal low = lpeg.Cc("\\low{%s}") * subscript * content / string.formatlocal high = lpeg.Cc("\\high{%s}") * superscript * content / string.formatlocal justtext = (1 - somescript)^1- Finally, the root element: 'moleculepattern'local parser moleculepattern = lpeg.Cs((csname + lowhigh + highlow + low + high + sign + anytext)^0)
userdatafunction thirddata.moleculeparser = parser molecule(string) -- * `:match` returns the matched string. Our pattern -- `moleculepattern` should match the entire input string. Any -- *performed* substitutions are retained. (`.Cs()` performs a -- previously defined substitution.) -- * `context()` inserts the resulting string into the stream, ready for -- TeX to evaluate. context(moleculepattern:match(string))end
function userdata.molecule(str)
return parser:match(str)
end
This is more verbose than the TeX solution, but is easier to read Quite terse and write. With a proper readable by parserstandards, I do not have to use tricks to check if either one or both <code>_</code> and <code>^</code> are present. More importantly, anyone (once they know the lpeg syntax) can read the parser and easily understand what isn't it does. This is in contrast to the implementation based on TeX macro jugglery which require you to implement a TeX interpreter in your head to understand.?
Writing macros that manipulate verbatim text involve catcode finesse ''This example demonstrates defining a custom \start...\stop buffer that only TeX wizards can mastergets processed through Lua in its entirety.''
Consider a simple example. Suppose we want to write an environment <code>\startdedentedtyping</code> ... <code>\stopdedentedtyping</code> that removes the indentation of the first line from every line. Thus, the output of ...
I don't even know how to write Defining an environment in TeX that will remove removes the leading spaces but leave leavesother spaces untouchedis complicated. On the other hand, once we capture the contents of the environment, removing the leading indent or ''dedenting'' the content in Lua is easy. Here is a Lua function that uses lpegsimple stringsubstitutions.
local newline = lpeg.P("\n\r") + lpeg.P("\r\n") + lpeg.P("\n") + lpeg.P("\r") local splitter = lpeg.Ct(lpeg.splitat(newline)) local lines = lpegstring.matchsplitlines(splitter, content)
indent = lpeg.P(indent) local any pattern = lpeg'^' ..Cs(1) local parser = indent * lpeg.C(any^0)
A more robust solution is to use ConTeXt's built in support for buffers. Using buffers, the above macro can be written as <texcode>% Create an environment that stores everything
Unlike MkII, where the contents of a buffer were written to an external file, in MkIV buffers are stored in memory. Thus, with LuaTeX is really simple to manipulate verbatim text: pass the contents of the environment to Lua; use Lua functions to do the text-manipulation; and in Lua call [[cld|<code>context.something()</code>]] functions to produce the ConTeXt code you want.
LuaTeX is removing many TeX barriers: using system fonts, reading and writing Unicode files, typesetting non-Latin languages, among others<texcode>\directlua% {tex. However, the biggest feature of LuaTeX is the ability to use a high-level programming language to program TeX. This can potentially lower the learning curve for programming TeXprint("Depth 1 \\directlua{tex.print('Depth 2')}")}</texcode>
In For more on this article, I have mentioned only one aspect of programming TeXsee the [http: macros that manipulate their input and output some text to the main TeX stream//wiki.luatex. Many other kinds of manipulations are possible: LuaTeX provides access to TeX boxes, token lists, dimensions, glues, catcodes, direction parameters, math parameters, etcorg/index. The details can be found in php/Writing_Lua_in_TeX] article on the [http://wwwwiki.luatex.org/documentationindex.html php/Main_Page LuaTeX manualwiki].
Programming in LuaTeX (view source)
Revision as of 09:06, 22 September 2015
, 09:06, 22 September 2015Corrected typo in URL to lpeg
<texcode>
$2 + 5 \defneq \DIVIDE#1#2ctxlua{context(3+5)}$, but is equal to \directluactxlua{tex.printcontext(#1/#2+5)}.This is \ctxlua{context(string.upper("absolutely"))}true.
</texcode>
<texcode>
\ctxlua
{-- A Lua comment
tex.print("This is not printed")}
\ctxlua
{% A Tex comment
tex.print("This is printed")}
</texcode>
<texcode>
% This doesn't work:
%\ctxlua
% {local t = {1,2,3,4}
% tex.print("length " .. #t)}
\ctxlua
{local t = {1,2,3,4}
</texcode>
<texcode>
\startluacode
\stopluacode
</texcode>
The contents full list of canonical namespaces, taken from [http://minimals.contextgarden.net/current/context/alpha/tex/context/base/luat-ini.lua luat-ini.lua]: <code>\startluacode<pre>userdata = userdata or { } -- for users (e.g. functions etc)thirddata = thirddata or { } -- only for third party modulesmoduledata = moduledata or { } -- only for development teamdocumentdata = documentdata or { } -- for users (e.g. raw data)parametersets = parametersets or { } -- experimental for team</pre></code> If your module, environment, or document is going to be used by other people, you should create your own subnamespaces within these tables. <code><pre>moduledata['mymodule'] = { }mm = moduledata.mymodulefunction mm. mainfunction() -- do stuffend<code/pre>\stopluacode</code> = Putting stuff in your TeX document from Lua = == Simple printing: context(), like the argument of tex.print(), and tex.sprint() ==Use <code>\ctxluacontext(...)</code> are fully expandedfor most things. It is equivalent to <code>tex.print(string.format(. '''This mean that even the Lua comments should be valid TeX statements!''' For example..))</code>,so
<texcode>
\startluacode
\stopluacode
</texcode>
<texcode>
</texcode>
<texcode>
\startluacode
\stopluacode
<texcode> \CHOOSERANDOMchapter[first]{"Some title} \startcolumns[n=3, rule=on] Hello one", " \column Hello two", " \column Hello three"} \stopcolumns
</texcode>
== Making \command{| |- | '''user'''arg1}{arg2} hook into Lua == | First, define a private user instance |- | '''third''' | third party module instance |- | '''module''' | ConTeXt module instance |- | '''isolated''' | an isolated instance |}Lua function:
<texcode>
\startusercodestartluacode math.randomseed( global -- remember, using the userdata namespace prevents conflicts userdata = userdata or {} function userdata.os.timesurroundwithdashes() str) function random context("--" ..str .."--") global.context(arg[math.random(1, #arg)])end\stopluacode</texcode> endThen define the TeX command that expands to a <code>\stopusercodectxlua</code> call:
<texcode>\def\CHOOSERANDOMsurroundwd#1% {\usercodectxlua{randomuserdata.surroundwithdashes([==[#1]==])}}
</texcode>
<texcode>
</texcode>
<texcode>
</texcode>
Doing simple arithmetic in TeX can be extremely difficult, as illustrated by the division macro in the introduction. With Lua, simple arithmetic becomes trivial. For example, if you want a macro to find the cosine of an angle (in degrees), you can write
<texcode>
\def\COSINE#1%
$\pi = \ctxlua{context(math.pi)}$
</texcode>
or , if you want less precision (notice the percent sign is escaped):
<texcode>
$\pi = \ctxlua{context("\%.6f", math.pi)}$
</texcode>
Notice that the percent sign is escaped.
== Loops without worrying about expansion ==
Loops in TeX are tricky , because macro assignments and macro expansion interact in strange ways. For example, suppose we want to typeset a table showing the sum of the roll of two dice and want the output to look like this:
<context source="yes">
\setupcolors[state=start]
</context>
<texcode>
\bTABLE \bTR \bTD $(+)$ \eTD \dorecurse{6} {\bTD \recurselevel \eTD} \eTR \dorecurse{6} {\bTR \bTD \recurselevel \eTD \edef\firstrecurselevel{\recurselevel} setupcolors[state=start] \dorecurse{6} {\bTD \the\numexpr\firstrecurselevel+\recurselevel \eTD}% \eTR} \eTABLE</texcode> HoweversetupTABLE[each][each][width=2em, this does not work as expectedheight=2em, yielding all zeros. A natural table stores the contents of all the cells, before typesetting it. But it does not expand the contents of its cell before storing them. Soalign={middle, at the time the table is actually typeset, TeX has already finished the <code>\dorecurse</code> and <code>\recurselevel</code> is set to 0. The solution is to place <code>\expandafter</code> at the correct location(s) to coax TeX into expanding the <code>\recurselevel</code> macro before the natural table stores the cell contents. The difficult part is figuring out the exact location of <code>\expandafter</code>s. Here is a solution that works: <texcode>\bTABLE \bTR \bTD $(+)$ \eTD \dorecurse{6middle} ] {\expandafter \bTD \recurselevel \eTD} \eTR \dorecurse{6} {\bTR \edef\firstrecurselevel{\recurselevel} setupTABLE[r][1][background=color,backgroundcolor=gray] \expandafter\bTD \recurselevel \eTD \dorecurse{6} {\expandafter\bTD \the\numexpr\firstrecurselevel+\recurselevel \relax \eTD} \eTR} \eTABLE </texcode> We only needed to add three <code>\expandafter</code>s to make the naive loop work. Nevertheless, finding the right location of <code>\expandafter</code> can be frustratingsetupTABLE[c][1][background=color, especially for a non-expert.backgroundcolor=gray]
\startluacode
context.bTABLE()
</texcode>
''This example demonstrates parsing simple ASCII notation with Lua's lpeg parser.''
As an example, let's consider typesetting chemical molecules in TeX. Normally, molecules should be typeset in text mode rather than math mode.
If we want
:H<sub>4</sub>SO<sub>4</sub><sup>+</sup>,
we must type
:<code>H\low{3}SO\lohi{4}{\textplus}</code>,
but we'd much rather type
:<code>\molecule{H_3SO_4^+}</code>.
<texcode>
\newbox\chemlowbox \def\chemlow#1% {\setbox\chemlowbox \hbox{{\switchtobodyfont[small]#1}}} startluacode
function formatters.high(one) return string.format("\def\domolecule#1high{#1\finishchem\egroup%s}", one)</texcode>end
-- a ^ or _ affects either a single character, or a brace-delimited-- block. Whichever it is, call it `content`.local subscript single = lpeg.P("_")character + plus + minuslocal superscript multiple = lpeg.P("leftbrace * single^")1 * rightbracelocal somescript content = subscript single + superscriptmultiple
-- These are our top-level elements: non-special text, of course, and-- blocks of superscript/subscript/both.-- lpeg.Cs(content) does two things:-- (1) not all matches go into the `/ function` construction; only-- *captures* go in. The C in Cs stands for Capture. This way, -- the superscript/subscript mark gets discarded.-- (2) it expands plus/minus before they go into the formatter. The-- s in Cs stands for 'substitute in the replacement values, if any'local text = single^1local low = subscript * lpeg.Cs(content ) / formatters.lowlocal high = superscript * lpeg.Cs(content) / formatters.highlocal lowhigh = subscript * lpeg.Cs(content) * superscript * lpeg.Cs(content) / formatters.lowhighlocal highlow = superscript * lpeg.Cs(csname + nested content) * + sign + any subscript * lpeg.Cs(content) / formatters.highlow
\stopluacode
\def\molecule#1% {\ctxlua{userdatathirddata.molecule("#1")}} \starttext \molecule{Hg^+}, \molecule{SO_4^{2-}}\stoptext</texcode>
== Manipulating verbatim text for dummies ==
<texcode>
... even though the leading whitespace is different.
<texcode>
\startluacode
-- Initialise Initialize a userdata namespace name space to keep our own functions in.
-- That way, we won't interfere with anything ConTeXt keeps in
-- the global namespacename space.
userdata = userdata or {}
function userdata.dedentedtyping(content)
local indent = string.match(lines[1], '^ +') or ''
for i=1,#lines do
lines[i] = lpegstring.matchgsub(parser, lines[i],pattern,"")
end
-- does.
end
\stopluacode</texcode>The only hard part is capturing the content of the environment and passing it to Lua. As explained in [[Inside_ConTeXt#Passing_verbatim_text_as_macro_parameter|Inside ConText]], the trick to capturing the content of an environment verbatim is to ensure that spaces and newlines have a catcode that makes them significant. This is done using <code>\obeyspaces</code> and <code>\obeylines</code>. Using that trick, we can write this macro as
Here is the code for defining the <texcodecode>\unprotect\def\startdedentedtyping% {\begingroup \obeyspaces \obeylines \long\def\dostartdedentedtyping##1\stopdedentedtyping% {\ctxlua{userdata.dedentedtyping(\!!bs \detokenize{##1} \!!es)}% \endgroup}% \dostartdedentedtyping}\protect</texcode>The above macro works for simple cases, but there are some limitations. For example, there is an extra space of <code>.\nstopdedentedtyping</code> in the output. This macro will also fail if the contents have unbalanced braces (try removing the <code>}</code> from the example).pair:
% between \startdedentedtyping and \stopdedentedtyping
% in a buffer named 'dedentedtyping'.
\def\stopdedentedtyping
{\ctxlua
{userdata.dedentedtyping(buffers.getcontent('dedentedtyping'))}}
</texcode>
That's all. Finally, we will go into a little more detail on how TeX and Lua communicate with each other. = Conclusion In detail: the interaction between TeX and Lua = To a first approximation, the interaction between TeX and Lua is straightforward. When TeX (i.e., the LuaTeX engine) starts, it loads the input file in memory and processes it token by token. When TeX encounters <code>\directlua</code>, it stops reading the file in memory, <em>fully expands the argument of <code>\directlua</code></em>, and passes the control to a Lua instance. The Lua instance, which runs with a few preloaded libraries, processes the expanded arguments of <code>\directlua</code>. This Lua instance has a special output stream which can be accessed using <code>tex.print(...)</code>. The function <code>tex.print(...)</code> is just like the Lua function <code>print(...)</code> except that <code>tex.print(...)</code> prints to a <em>TeX stream</em> rather than to the standard output. When the Lua instance finishes processing its input, it passes the contents of the <em>TeX stream</em> back to TeX.<ref>The output of <code>tex.print(...)</code> is buffered and not passed to TeX until the Lua instance has stopped.</ref> TeX then inserts the contents of the <em>TeX stream</em> at the current location of the file that it was reading; expands the contents of the <em>TeX stream</em>; and continues. If TeX encounters another <code>\directlua</code>, the above process is repeated. As an exercise, imagine what happens when the following input is processed by LuaTeX. The answer is in the footnotes. <ref>In this example, two different kinds of quotations are used to avoid escaping quotes. Escaping quotes inside <code>\directlua</code> is tricky. The above was a contrived example; if you ever need to escape quotes, you can use the <code>\startluacode ... \stopluacode</code> syntax.</ref>
= Notes =
<references />
{{note | This article is originally based on [https://www.tug.org/members/TUGboat/tb30-2/tb95mahajan-luatex.pdf this TugBoat article ]. Feel free to modify it.}}
[[Category:Lua]]
[[Category:LuaTeX]]
