2
edits
Changes
Jump to navigation
Jump to search
m
{{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 lua to write macros in [[LuaTeX]]. I give some examples The interweaving of ConTeXt and Lua 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 lua in luaTeX. These examples include macros that do arithmetic on their argumentsonce inside Lua, 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 {{cmd|ctxlua}}, and the environment {{cmd|startluacode}}…{{cmd|stopluacode}}. Both are wrappers around the LuaTeX primitive {{cmd|directlua}}, which you should never need to use. In general, you will define a function inside a {{cmd|startluacode}} block, and then define a TeX command that calls the function using {{cmd|ctxlua</code>, especially because {{cmd|ctxlua}} has a few idiosyncracies.
As its name suggests, [[LuaTeX]] adds lua, <blockquote>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 examplemeans that all the Lua code, even the comments, consider a must be valid TeX macro that divides two numbers!''' A string like {{cmd|undefined}} will cause an immediate failure. Such a macro is provided by the <tt>fp</ttblockquote> package and also by == Calling a bit of Lua inline: {{cmd|ctxlua}} == The command {{cmd|ctxlua}} is for short inline snippets of Lua, suchas <tttexcode>pgfmath$2 + 5 \neq \ctxlua{context(3+5)}$, but is equal to \ctxlua{context(2+5)}.This is \ctxlua{context(string.upper("absolutely"))} true.</tttexcode> library of {{cmd|ctxlua}} operates under the <tt>TikZ</tt> packagenormal TeX catcodes (category codes). The This means the following comment is from two things for the Lua code inside:* all newlines get treated as spaces* special TeX characters like &, #, $, {, }, etc., need to be escaped. In addition, the warning above still holds. All the Lua code, even the comments, must be valid TeX. Some code to illustrate the <tt>fp</tt> packagenewline problem:
Thus, with luaTeX ordinary users can write simple macros; and, perhaps more importantly, can read and understand macros written by TeX wizards.
Since == Calling a lua function with {{cmd|cldcontext}} and get the luaTeX project started it has been actively supported by ConTeXt. <ref>Not surprising, as two of luaTeX's main developers—Taco Hoekwater return == One can execute a Lua code from within TeX and Hans Hagen—are also get back the main ConTeXt developersresult in TeX by using {{cmd|cldcontext}}.</ref> These daysThus, the various <em>How do I write such if {{code|myfunction}} is a macro</em> questions on the ConTeXt mailing list are answered by function of a solution that uses lua. I present a few such examples variable {{code|x}} defined in this article. I have deliberately avoided examples about [[Fonts Lua, {{cmd|cldcontext|{myfunction(5)}}} returns the value {{code|myfunction(5)}} in LuaTeX | fonts]] and non-Latin languagesTeX. There This is already quite a bit of documentation about them. In this article, I highlight how equivalent to use luaTeX to write macros that require some <em>flow control</em>: randomized outputs, loops, and parsing{{cmd|ctxlua|{context(myfunction(5))}}}.
= 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. == A larger Lua block: {{cmd|startluacode}}…{{cmd|stopluacode}} ==
As an exerciseInside the {{cmd|startluacode}}…{{cmd|stopluacode}} environment, imagine what happens when newlines and special characters behave normally. This solves the following input is processed by luaTeXcatcode problem that {{cmd|ctxlua}} suffers from. <ref>In this exampleApart from these special characters, I used two different kinds of quotations to avoid escaping quotes. Escaping quotes inside <code>\directlua</the main warning remains in force: all the Lua code> is tricky. The above was a contrived example; if you ever need to escape quotes, you can use even the <code>\startluacode ... \stopluacode</code> syntax explained latercomments, must be valid TeX.</ref>
On top The full list of these luaTeX primitivescanonical namespaces, ConTeXt provides a higher level interfacetaken from [https://distribution. There are two ways to call lua from ConTeXtcontextgarden.net/current/context/latest/tex/context/base/mkxl/luat-ini.lmt luat-ini. The first is a macro lmt]: <code>\ctxlua</codepre> userdata = userdata or { } -- for users (read as ConTeXt luae.g. functions etc), which is similar to 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<code/pre>\directlua</code>. (Aside: It If your module, environment, or document is possible going to run the lua instance under different name spacesbe used by other people, you should create your own subnamespaces within these tables. <code>\ctxlua</codepre> is the default name space; other name spaces are explained latermoduledata['mymodule'] = { }mm = moduledata.mymodulefunction mm.mainfunction() -- do stuffend<code/pre>\ctxlua</code> is good for calling small snippets of lua. The argument of < == Undefined Commands in Lua Comments == Lua code>\ctxlua</code> is parsed under normal invoked inside TeX doesn’t allow 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 ignoredundefined commands ''even inside comments''.
This can be avoided by using a TeX comment instead of a lua comment. However, To get the sample above working under normal TeX catcodes poses a bigger problem(as [https: special TeX characters like &, #, $, {, }, etc//www.mail-archive., need to be escapedcom/ntg-context@ntg. For example, # has to be escaped with <code>\string<nl/code> to be used msg103892.html explained by Hans in <code>\ctxlua</code>a NTG-context thread from jan.2023 entitled “Minor bug in Lua or ConTeXt”]), you would need a fallback definition:
As the argument of <code>\ctxlua</code> {{cmd|undefinedcommandfromme}} gets only defined (as {{cmd|relax}}, to do nothing), if and only if it is fully expanded, escaping characters can sometimes be trickyundefined. To circumvent this problem = Calling TeX from Lua = Being a topic on itself, pages are dedicated:* '''[[CLD|ConTeXt defines a environment called <code>\startluacode Lua Documents]]''', or CLD, are way to access TeX from inside Lua scripts.A page give clues about [[CLD_passing_variables|passing variables]] within CLD (2018).. \stopluacode<* [[Lua|Wiki page dedicated to Lua]]** [[Extensions to the Lua I/code>O library]]** [[String manipulation]]** [[Table manipulation]] = Putting stuff in your TeX document from Lua = == Simple printing: context(), tex. This sets the catcodes to what one would expect in luaprint(), and tex. Basically only sprint() ==Use <code>\context(…)</code> has its usual TeX meaning, the catcode of everything else for most things. It is set equivalent to other. So, for all practical purposes, we can forget about catcodes inside <code>\startluacode tex.print(string.. \stopluacodeformat(…))</code>. The above two examples can be written as, so
-- A lua comment tex.print(name = "This is printed.Jane") local t date = {1,2,3,4}"today" tex.printcontext("length Hello %s, how are you %s?" .. #t, name, date)-- Becomes 'Hello Jane, how are you today?'
This environment is meant for moderately sized More primitively, you have <code>tex.print()</code> and <code snippets>tex. For longer lua sprint()</code>. Either one can take as an argument either a number of strings, it or an array of strings, and will then insert the strings into the TeX stream. The only difference is more convenient to write the that <code>tex.print()</code in > treats each string as a separate lua file and then load it using lua's input line, while <code>dofiletex.sprint(...)</code> functiondoesn't. So the following lines
ConTeXt also provides a lua function to conveniently write to the TeX stream. The function is called <codetexcode>context\ctxlua{tex.print("a", "b")}\ctxlua{tex...print({"a", "b"})}</codetexcode> are both interpreted by TeX as <texcode>ab</texcode> and it is equivalent to but when we use <code>tex.print(string.format(...))sprint</code>. instead, either of the following
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.sprint("\%Xa",#1"b")}}\TOHEXctxlua{35tex.sprint({"a", "b"})}
The percent sign had to will be escaped because read by TeX as <codetexcode>\ctxluaab</codetexcode> assumes TeX catcodes without any space in between. Sometimes == Context commands == Most commands that you would type with a backslash in plain ConTeXt, escaping arguments you can be difficult; instead, it can be easier to define a lua function inside access from Lua 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.comnl/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 lua functions defined in luaTeX article on [[CLD|ConTeXt Lua documents]], and ConTeXtalso, again, the [http://www.pragma-ade.nl/general/manuals/cld-mkiv.pdf CLD manual].
In order to avoid name clashes, = Passing arguments and buffers: ConTeXt also defines independent name spaces of lua instances. They are commands that hook into Lua =
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 <code>random</code> in the <code>user</code> instance of lua, I did not bother to use a separate name space for the function. The lua functions <code>os.time</code>, which is defined by a luaTeX library, and <code>context</code>, which is defined by ConTeXt, needed to be accessed through a <code>global</code> name space. On the other handNext, we define the <code>math.randomseed</code> function, which is part start command of lua, could be accessed as is. our custom buffer:
A separate lua instance also makes debugging slightly easier. With <code>\ctxlua</code> the error message starts with
! LuaTeX error <main ctx instance>\def\startverynarrow% {\dostartbuffer [verynarrow] % buffer name [startverynarrow] % command where buffer starts [stopverynarrow]} % command where buffer ends % also:command invoked when buffer stops
With Lastly, we define the {{cmd|stopverynarrow}} command such that it passes the recently-complated buffer to our <code>\usercodeverynarrow</code> the error message starts withLua function:
! LuaTeX error <private user instance>:\def\stopverynarrow {\ctxlua {userdata.verynarrow(buffers.getcontent('verynarrow'))}}
This makes And that's it easier to narrow down the source ! The rest of errorthis article will consist of examples.
Normally, it is best to define your lua functions in the <code>user</code> name space. If you are writing a module, then define your lua functions in the <code>third</code> instance and in a name space which is the name 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 space.= 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 a abacus =''This example demonstrates writing simple commands that invoke \ctxlua.''
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:
However, this does not work as expected, 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. So, 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{6}
{\expandafter \bTD \recurselevel \eTD}
\eTR
\dorecurse{6}
{\bTR
\edef\firstrecurselevel{\recurselevel}
\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 frustrating, especially for a non-expert.
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 {{cmd|molecule}} 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 exampleformat("\\lohi{%s}{%s}", one, the above <code>\molecule</code> macro can be written astwo)end
<texcode>-- These are the characters we may encounter-- The `/` means we want to expand + and - to \startluacodetextplus c.q. \textminus;-- this substition is not instant, but will take place inside the first -- surrounding lpeg.Cs() call.local plus = lpeg.P("+") / "\\textplus "userdata local minus = userdata or lpeg.P("-") / "\\textminus "local character = lpeg.R("az", "AZ", "09") -- R is for 'range'local subscript = lpeg.P("_") -- P is simply for 'pattern'local superscript = lpeg.P("^")local leftbrace = lpeg.P("{")local rightbrace = lpeg.P("}")
local lowercase = lpeg.R("az")local uppercase = lpeg.R("AZ")local backslash = lpeg.P("\\")local csname = backslash * lpeg.P(1) * (1-backslash)- a ^0or _ affects either a single character, or a brace-delimitedlocal plus = lpeg-- block.P("+") / "\\textplus "local minus = lpegWhichever it is, call it `content`.P("-") / "\\textminus "local digit = lpeg.R("09")local sign single = character + plus + minuslocal cardinal = digit^1local integer = sign^0 * cardinallocal leftbrace = lpeg.P("{")local rightbrace multiple = lpeg.P("}")local nobrace = 1 - (leftbrace + rightbrace)local nested = lpeg.P {leftbrace * (csname + sign + nobrace + lpeg.V(single^1))^0 * rightbrace}local any content = lpeg.P(1)single + multiple
local lowhigh = lpegfunction thirddata.Ccmolecule("\\lohi{%s}{%s}"string) * subscript * content * superscript -- * content / `:match` returns the matched string.formatOur patternlocal highlow = lpeg -- `moleculepattern` should match the entire input string.Cc("\\hilo{%s}{%s}") Any * superscript -- * content performed* subscript * content / stringsubstitutions are retained.formatlocal low = lpeg(`.CcCs("\\low{%s}") ` performs a * subscript -- * content / stringpreviously defined substitution.format)local high = lpeg.Cc -- * `context("\\high{%s}") * superscript * content / ` inserts the resulting string.formatinto the stream, ready forlocal justtext -- = (1 - somescript)^1TeX to evaluate.local parser = lpeg.Cscontext(moleculepattern:match(csname + lowhigh + highlow + low + high + sign + anystring)^0)end
userdata.moleculeparser = parser \stopluacode
function userdata\def\molecule#1{\ctxlua{thirddata.molecule(str"#1") return parser:match(str)end\stopluacode}}
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 ''This example demonstrates defining a custom {{cmd|start}}…{{cmd|stop}} buffer that manipulate verbatim text involve catcode finesse that only TeX wizards can mastergets processed through Lua in its entirety.''
Consider a simple example. Suppose we want to write an environment <code>\{{cmd|startdedentedtyping</code> ... <code>\}} … {{cmd|stopdedentedtyping</code> }} that removes the indentation of the first line from every line. Thus, the output of…
#include <<stdio.h>> void main() { print("Hello world \n") ; }
'''Note''' the difference in whitespace at the beginning of each line. 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 Lua is easy. Here is a lua 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% On closing the dedentedtyping environment, call the LuaTeX% function dedentedtyping(), and pass it the contents of % the buffer called 's built in support for dedentedtyping'\def\stopdedentedtyping {\ctxlua {userdata.dedentedtyping(buffers. Using buffers, the above macro can be written asgetcontent('dedentedtyping'))}}</texcode>
<texcode>\def\startdedentedtyping {\dostartbuffer[dedentedtyping][dostartdedentedtyping][stopdedentedtyping]}That's all. Finally, we will go into a little more detail on how TeX and Lua communicate with each other.
\def\stopdedentedtyping== Other examples == {\ctxlua{userdata.dedentedtyping* [[Calculations_in_Lua|Calculations in Lua]] (buffers.contentwarning date 2012)* [[LPeg|Writing a parser with LPeg]] ('dedentedtyping'Lua Parsing Expression Grammars))}}</texcode>Unlike MkII, where the contents of a buffer were written to an external file, * [[Random|Random numbers]] in MkIV buffers are stored in memory. Thus, ConTeXt and MetaPost* [[SQL|An example with luatex is really simple to manipulate verbatim textSQL database]]* [[Pascal's Triangle]] = In detail: write the text manipulating code in lua interaction between TeX and pass the contents of the environment to the lua function using buffers.Lua =
= Conclusion =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 {{cmd|directlua}}, it stops reading the file in memory, <em>fully expands the argument of {{cmd|directlua}}</em>, and passes the control to a Lua instance. The Lua instance, which runs with a few preloaded libraries, processes the expanded arguments of {{cmd|directlua}}. 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 {{cmd|directlua{{cmd|, the above process is repeated.
luaTeX As an exercise, imagine what happens when the following input is removing many TeX barriers: using system fonts, reading and writing Unicode files, typesetting non-Latin languages, among othersprocessed by LuaTeX. The answer is in the footnotes. However<ref>In this example, the biggest feature two different kinds of luaTeX quotations are used to avoid escaping quotes. Escaping quotes inside {{cmd|directlua}} is the ability to use tricky. The above was a high-level programming language contrived example; if you ever need to program TeX. This escape quotes, you can potentially lower use the learning curve for programming TeX{{cmd|startluacode}}…{{cmd|\stopluacode{{cmd| syntax.</ref>
In <texcode>\directlua% {tex.print("Depth 1 \\directlua{tex.print('Depth 2')}")}</texcode> 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 luaTeX manualphp/Main_Page LuaTeX wiki].
→Undefined Commands in Lua Comments: Fix a broken link. And add enough information to be able to re-fix it easily. (I guess this last part could go in a footnote reference, but I am not sure how to do that properly…)
<texcode>
\def\FP@div#1#2.#3.#4\relax#5.#6.#7\relaxctxlua {%-- A Lua comment % [ tex...] algorithmic idea print(for x>0, y>0"This is not printed")} % - %determine \FP@shift such that % y*10^\FP@shift < 100000000ctxlua % <=y*10^(\FP@shift+1) % - {%determine \FP@shift' such that A Tex comment % x*10^\FP@shift'< 100000000 % <=x*10^ tex.print(\FP@shift+1"This is printed") % - x=x*\FP@shift' % - y=y*\FP@shift % - \FP@shift=\FP@shift-\FP@shift' % - res=0 % - while y>0 %fixed-point representation! % - \FP@times=0 % - while x>y % - \FP@times=\FP@times+1 % - x=x-y % - end % - y=y/10 % - res=10*res+\FP@times/1000000000 % - end % - %shift the result according to \FP@shift}
</texcode>
The problem with special TeX characters. (<ttcode>pgfmath#t</ttcode> library implements the macro in a similar way, but limits the number of shifts that it does. These macros highlight is Lua for 'the state length 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 array <code>/t</code> operator (I will explain the details later.):
<texcode>
% This doesn't work:%\def\DIVIDE#ctxlua% {local t = {1,2,3,4}% tex.print("length " .. #2t)}\ctxlua {\directlualocal t = {1,2,3,4} tex.print("length " .. \string#1/#2t)}}
</texcode>
<texcode>
\directlua%startluacode {tex -- 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 ..print", ") end context("Depth 1 0!") -- \\directlua{texpar 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 \\#\\$\\& printthe escape characters, too.")\stopluacode</texcode> == Putting Lua code in an external file == You can put your lua code in an external file ('Depth 2'with the <code>.lua</code> extension)}and include it with the <code>require</code> command: <texcode>\startluacode-- include the file my-lua-lib.luarequire("my-lua-lib")\stopluacode</texcode> == Namespaces == It is a good habit to put your custom-defined functions in their own namespace. The traditional namespace for this is <code>userdata</code>:<texcode>\startluacode -- if userdata doesn't exist yet, create it userdata = userdata or {} -- define a shorter synonym u = userdata -- create my custom function inside the userdata namespace function u.myfunction() -- do stuff end\stopluacode
</texcode>
<texcode>
\starttext\startluacode--\undefinedcommandfromme\stopluacodeHello\ctxlua {-- A lua comment\undefinedcommandfromme} tex.print("This is not printed")}\stoptext
</texcode>
<texcode>
\ctxlua {local t = {1,2,3,4} tex.print("length " .. ifdefined\string#t)}undefinedcommandfromme \else \let\undefinedcommandfromme\relax \fi
</texcode>
<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 -- remember, using the userdata namespace prevents conflicts userdata = userdata or {} function userdata.randomseedsurroundwithdashes(str) context( global"--" .os.timestr .. "--") end\stopluacode</texcode> Then define the TeX command that expands to a {{cmd|ctxlua}} call: <texcode>\def\surroundwd#1% {\ctxlua{userdata.surroundwithdashes([==[#1]==]) )}}</texcode> ''NB'': quoting with <code>[==[#1]==]</code> function random([http://www.lua.org/manual/5.2/manual.html#3.1 long strings]) globalworks just like <code>"#1"</code> in most cases, but in addition it is robust against <code>#1</code> containing the quotation mark<code>"</code> which would terminate the Lua string prematurely.Inside {{cmd|protect}}…{{cmd|unprotect}} the macros {{cmd|!!bs}}and {{cmd|!!es} are at your disposition.They are equivalent to <code>[===[</code> and <code>]===]</code> and --being single tokens to TeX -- parsed faster.context(argSee [mathhttp://repo.or.cz/w/context.git/blob/refs/heads/origin:/tex/context/base/luat-ini.random(1, mkiv#arg)l174 <code>luat-ini.mkiv</code>].) end== Making {{cmd|startenv}}…{{cmd|stopenv}} hook into Lua ==The first job is, as ever, to have the Lua function at the ready<texcode>\stopusercodestartluacode userdata = userdata or {}
function userdata.verynarrow(buffer) -- equivalent to \def\CHOOSERANDOM#1%startnarrower[10em] context.startnarrower({\usercode{random"10em"}) context(buffer) context.stopnarrower(#1)}} end\stopluacode
</texcode>
<texcode>
</texcode>
<texcode>
</texcode>
Doing simple arithmetic in TeX can be extremely difficult, as illustrated by the division macro in the introduction. With luaLua, 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>
$\pi = \ctxlua{context("\%letterpercent.6f", math.pi)}$
</texcode>
Notice that the percent sign is escaped with letterpercent.
= Loops without worrying about expansion == mathexpr with LMTX ===
In LMTX there is a new way to use calculated expressions with mathexpr through ([https://github.com/contextgarden/context-mirror/blob/7fd782dace8f90e7e032ca8f449f8ca4eada450b/doc/context/sources/general/manuals/math/math-fun.tex math-fun]). Some examples are: <texcode>$ \pi = \mathexpr[.40N]{pi} $$ \pi = \mathexpr[.80N]{sqrt(11)} $$ \pi = \decimalexpr[.80N]{sqrt(11)} $$ \pi = \decimalexpr{sqrt(11)} $$ c = \complexexpr{123 + new(456,789)} $</texcode> == Loops without worrying about expansion == ''This example demonstrates using Lua to write a quasi-repetitive piece of ConTeXt code.'' 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} setupcolors[state=start] \eTR \dorecursesetupTABLE[each][each][width=2em,height=2em,align={6middle,middle} ] {\bTR setupTABLE[r][1][background=color,backgroundcolor=gray] \bTD \recurselevel \eTD \edef\firstrecurselevel{\recurselevel} \dorecurse{6} {\bTD \the\numexpr\firstrecurselevel+\recurselevel \eTD}% \eTR} \eTABLE</texcode>setupTABLE[c][1][background=color,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>3</sub>SO<sub>4</sub><sup>+</sup>,
we must type
:<code>H{{cmd|low|{3}}}SO{{cmd|lohi|{4}}}{{{cmd|textplus}}}</code>,
but we'd much rather type
:{{cmd|molecule|{H_3SO_4^+}}}.
<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
-- 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.PCs("_"content) / formatters.highlocal lowhigh = subscript * lpeg.Cs(content) * superscript = * lpeg.PCs("^"content) / formatters.lowhighlocal somescript highlow = superscript * lpeg.Cs(content) * subscript + superscript* lpeg.Cs(content) / formatters.highlow
-- Finally, the root element: 'moleculepattern'local content moleculepattern = lpeg.Cs(csname (lowhigh + highlow + nested low + sign high + anytext)^0)
\defstarttext \molecule#1% {Hg^+}, \ctxluamolecule{SO_4^{userdata.molecule("#1")2-}}\stoptext</texcode>
== Manipulating verbatim text for dummies ==
<texcode>
\startdedentedtyping
\stopdedentedtyping
</texcode>
… should be the same as the output of…
<texcode>
\starttyping
#include <<stdio.h>>
void main()
{
\stoptyping
</texcode>
… even though the leading whitespace is different.
<texcode>
\startluacode
-- Initialize a userdata name space to keep our own functions in.
-- That way, we won't interfere with anything ConTeXt keeps in
-- the global name 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 Here is capturing the content of code for defining the environment and passing it to lua. As explained in [[Inside_ConTeXt#Passing_verbatim_text_as_macro_parameter{{cmd|startdedentedtyping}} … {{cmd|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 asstopdedentedtyping}} pair:
<texcode>\unprotect\def% Create an environment that stores everything % between \startdedentedtyping% {and \begingroupstopdedentedtyping \obeyspaces \obeylines% in a buffer named 'dedentedtyping'. \long\def\dostartdedentedtyping##1\stopdedentedtyping%startdedentedtyping {\ctxlua{userdata.dostartbuffer [dedentedtyping(\!!bs \detokenize{##1} \!!es)}%] \endgroup}% [startdedentedtyping] \dostartdedentedtyping}\protect</texcode>The above macro works for simple cases, but there are some limitations. For example, there is an extra space of <code>\n</code> in the output. This macro will also fail if the contents have unbalanced braces (try removing the <code> [stopdedentedtyping]}</code> from the example.
= 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:Programming and Databases]]
