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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 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, and parse their argumentsthe appropriate functions to put things into the TeX stream.
As its name suggests, [[LuaTeX]] adds lua, a programming language, to TeX, the typesetter. This allows us to program TeX in a high-level programming language. For example, consider a TeX macro that divides two numbers. Such a macro is provided by the <tt>fp</tt> package and also by <tt>pgfmath</tt> library of the <tt>TikZ</tt> package. The following comment is from the <tt>fp</tt> package
\def\FP@div#1#$2.#3.#4+ 5 \relax#5.#6.#7neq \relaxctxlua{% % [...] algorithmic idea context(for x>03+5)}$, y>0) % - %determine but is equal to \FP@shift such that % y*10^\FP@shift < 100000000 % <=y*10^ctxlua{context(\FP@shift2+15)}. % - %determine This is \FP@shift' such that % x*10^\FP@shift'< 100000000 % <=x*10^ctxlua{context(string.upper(\FP@shift+1"absolutely")) % - 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} true.
The <tt>pgfmath</tt> library implements {{cmd|ctxlua}} operates under the macro in a similar way, but limits the number of shifts that it doesnormal TeX catcodes (category codes). These macros highlight This means the state of affairs in writing TeX macros. Even simple following two things like multiplying two numbers are hard; you either have to work extremely hard to circumvent for the programming limitations of Lua code inside:* all newlines get treated as spaces* special TeXcharacters like &, #, $, or{, more frequently}, hope that someone else has done the hard work for youetc., need to be escaped. In luaTeXaddition, such a function can be written using the <warning above still holds. All the Lua code>/</, even the comments, must be valid TeX. Some code> operator (I will explain to illustrate the details later)newline problem:
ThusThe problem with special TeX characters. (<code>#t</code> is Lua for 'the length of array <code>t</code>.)<texcode>% This doesn't work:%\ctxlua% {local t = {1,2,3,4}% tex.print("length " .. #t)}\ctxlua {local t = {1,2,3, 4} tex.print("length " .. \string#t)}</texcode> == Calling a lua function with luaTeX ordinary users {{cmd|cldcontext}} and get the return == One can write simple macros; execute a Lua code from within TeX andget back the result in TeX by using {{cmd|cldcontext}}. Thus, if {{code|myfunction}} is a function of a variable {{code|x}} defined in Lua, perhaps more importantly{{cmd|cldcontext|{myfunction(5)}}} returns the value {{code|myfunction(5)}} in TeX. This is equivalent to {{cmd|ctxlua|{context(myfunction(5))}}}. == A larger Lua block: {{cmd|startluacode}}…{{cmd|stopluacode}} == Inside the {{cmd|startluacode}}…{{cmd|stopluacode}} environment, can read newlines and understand macros written by special characters behave normally. This solves the catcode problem that {{cmd|ctxlua}} suffers from. Apart from these special characters, the main warning remains in force: all the Lua code, even the comments, must be valid TeX wizards. <texcode>\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!")
Since -- \\par is equivalent to a blank line in the input -- (Notice the luaTeX project started it has been actively supported by ConTeXt. <ref>Not surprising, as two of luaTeXescaped backslash: TeX won's 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 t mind 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 themabove comment. In this article, I highlight how to use luaTeX to write macros that require some <em>flow control</em>: randomized outputs, loops, and parsing) context.par()
= Interaction between TeX -- Look! we can use # and lua =$ with impunity! context("Unless we print them, then we must \\#\\$\\& print the escape characters, too.")\stopluacode</texcode>
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 <== Putting Lua 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 an external 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 You can put your lua code in an exercise, imagine what happens when external file (with the following input is processed by luaTeX. <refcode>In this example, I used two different kinds of quotations to avoid escaping quotes. Escaping quotes inside <code>\directlualua</code> is tricky. The above was a contrived example; if you ever need to escape quotes, you can use extension) and include it with the <code>\startluacode ... \stopluacoderequire</code> syntax explained later.</ref>command:
On top of these luaTeX primitives, ConTeXt provides == Namespaces == It is a higher level interface. There are two ways good habit to call lua from ConTeXtput your custom-defined functions in their own namespace. The first is a macro <code>\ctxlua</code> (read as ConTeXt lua), which traditional namespace for this is similar to <code>\directluauserdata</code>. (Aside: 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, 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 context.commands, see the function takes a list [http://www.pragma-ade.nl/general/manuals/cld-mkiv.pdf ConTeXt Lua document] manual. It is old, but most of words and chooses a random word among themit still applies. For an example One final note: arguments can also be specified in the form of such a conversionnested functions. Because LuaTeX evaluates the deepest-nested argument first, see this may cause the <emcode>sorting a list of tokenscontext()</emcode> page calls to be evaluated in the wrong order. For more on this, see the article on [[CLD|ConTeXt Lua documents]], and also, again, the [http://luatexwww.bluwikipragma-ade.comnl/general/gomanuals/Sort_a_token_list luaTeX wikicld-mkiv.pdf CLD manual]. = Passing arguments and buffers: ConTeXt commands that hook into Lua = == Making \command{arg1}{arg2} hook into Lua ==First, define a Lua function: <texcode>\startluacode -- remember, using the userdata namespace prevents conflicts userdata = userdata or {}
In the above, I created a name space called <code> function userdata.surroundwithdashes(str) context("--" .. str .. "--") end\stopluacode</code> and defined the function <code>random</codetexcode> in that name space. Using a name space avoids clashes with the lua functions defined in luaTeX and ConTeXt.
In order Then define the TeX command that expands to avoid name clashes, ConTeXt also defines independent name spaces of lua instances. They are a {{cmd|ctxlua}} call:
{|<texcode> |-\def\surroundwd#1% | '''user''' | a private user instance |- | '''third''' | third party module instance |- | '''module''' | ConTeXt module instance |- | '''isolated''' | an isolated instance {\ctxlua{userdata.surroundwithdashes([==[#1]==])}} |}</texcode>
Thus, for example, instead of ''NB'': quoting with <code>\ctxlua[==[#1]==]</code> and <code>\startluacode ([http://www.lua.org/manual/5. \stopluacode<2/code>, the manual.html#3.1 long strings])works just like <code>user"#1"</code> instance can be accessed via the macros in most cases, but in addition it is robust against <code>\usercode#1</code> and containing the quotation mark<code>\startusercode ... \stopusercode"</code>which would terminate the Lua string prematurely. In instances other than <code>isolated</code>, all Inside {{cmd|protect}}…{{cmd|unprotect}} the lua functions defined by ConTeXt (but not the inbuilt lua functions) macros {{cmd|!!bs}}and {{cmd|!!es} are at your disposition.They are stored in a equivalent to <code>global[===[</code> name space. In the and <code>isolated]===]</code> instance, all lua functions defined by ConTeXt are hidden and cannot be accessed--being single tokens to TeX -- parsed faster.(See [http://repo. Using these instances, we could write the above or.cz/w/context.git/blob/refs/heads/origin:/tex/context/base/luat-ini.mkiv#l174 <code>\CHOOSERANDOMluat-ini.mkiv</code> macro ].) == Making {{cmd|startenv}}…{{cmd|stopenv}} hook into Lua ==The first job is, as followsever, to have the Lua function at the ready
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 ==
= Getting text into LuaTex verbatim =''This example demonstrates parsing simple ASCII notation with Lua's lpeg parser.''
This section gives As an example code for passing , let's consider typesetting chemical molecules in TeX. Normally, molecules should be typeset in text to a call to a LuaTeX function verbatimmode rather than math mode. The first subsection shows how to define a macro If we want :H<sub>3</sub>SO<sub>4</sub><sup>+</sup>,we must type :<code>\DedentH{{cmd|low|{3}}}SO{{cmd|lohi|{4}}}{{{...cmd|textplus}}}</code> ,but we'd much rather type:{{cmd|molecule|{H_3SO_4^+}}}. So, we need a function that processes its argument in LuaTeX; can take a string like that, parse it, and turn it into the second subsection shows how to define an environment <appropriate TeX code>\startDedent .LuaTeX includes a general parser based on PEG (parsing expression grammar) called [http://www.inf.puc-rio. \stopDedent<br/~roberto/lpeg/code> that does lpeg.html lpeg], and it makes writing little parsers positively joyful. (Once you've got the sameknack of it, at least. First, however) For example, here is the LuaTeX <code>dedent()</code> functionabove {{cmd|molecule}} macro can be written as follows.
-- Keep we will put our own functions out of molecule function in the global userdata namespace. thirddata userdata = thirddata userdata or {}
thirddata.dedent = function(code) -- Finds out by how much The formatting functions into which the first line is indented, captured -- and dedents the entire block by that much.superscript/subscript blocks will be fed -- N.B. This function does not handle tabs.local formatters = { }
-- First some debugging stuff: dump the input to a text file -- to check that we got what we wantedfunction formatters.low(one) -- Feel free to delete these three lines return string. logfile = io.openformat("debug.txt\\low{%s}", "w") logfile:write(codeone) logfile:close()end
-- Now for the meat of itfunction formatters. -- How many leading spaces in the first line? lead = string.matchhigh(code, '^ +'one) or '' -- remove lead from every line code = return string.gsubformat(code"\\high{%s}", '^' .. lead, ''one) code = string.gsub(code, '\n' .. lead, '\n')end
function formatters.lowhigh(one, two) return string.format("\\lohi{%s}{%s}", one, two)end function formatters.highlow(one, two,three) return string.format("\\lohi{%s}{%s}", one,two)end -- print These are the resulting starttyping environment characters we may encounter-- The `/` means we want to expand + and - to \textplus c.q. \textminus;-- this substition is not instant, but will take place inside the TeX streamfirst -- (contextsurrounding lpeg.starttypingCs() doesn't seem to work)call.local plus tex= lpeg.sprintP("+") / "\\starttypingtextplus " local minus = lpeg.. P("-") / "\n\textminus " local character = lpeg.R("az", "AZ", "09") -- R is for 'range'local subscript = lpeg. P("_") -- P is simply for 'pattern' code local superscript = lpeg.P("^")local leftbrace = lpeg.P("{") local rightbrace = lpeg.P("\\stoptyping}" ) -- a ^ or _ affects either a single character, or a brace-delimited-- block. Whichever it is, call it `content`.local single = character + plus + minuslocal multiple = leftbrace * single^1 * rightbracelocal content = single + multiple -- 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. "\n"-- (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 end= 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(content) * subscript * lpeg.Cs(content) / formatters.highlow
\stopluacode-- Finally, the root element: 'moleculepattern'</texcode>local moleculepattern = lpeg.Cs((lowhigh + highlow + low + high + text)^0)
== A macro that passes its argument function thirddata.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 LuaTeX verbatim ==evaluate. context(moleculepattern:match(string))end
<!-- wikify \obeylines, \obeyspaces, \begingroup, \normalunexpanded -->This code uses the two-macro pattern. The first macro begins a grouping with<code>\begingroup</code>, initialises <code>\obeylines</code> and<code>\obeyspaces</code>, and finally calls <code>\doDedent</code>. The<code>\doDedent</code> macro, after performing the call to LuaTex, then closesthe grouping, thereby turning off the no-longer-needed<code>\obeylines</code>and <code>\obeyspaces</code>. Macros' contents get expanded before they areevaluated, so if this were all one single macro its argument <code>#1</code>would get expanded the normal way before the <code>\obey...</code> could takeeffect.stopluacode
<texcode>%% This code is due to Wolfgang Schuster on the ntg-ConTeXt mailing list.\unprotect % Two-macro structure to define \Dedent{...} \def\Dedent{\begingroup\obeylines\obeyspaces\doDedent} \def\doDedentmolecule#1{\directluactxlua{ thirddata.dedentmolecule(\!!bs\normalunexpanded{"#1}\!!es")} \endgroup}\protect
% Try it out
== An environment that passes its contents to LuaTeX verbatim ==Quite terse and readable by parser standards, isn't it?
There are two ways to define a startstop environment so that it passes itscontents to LuaTeX == Manipulating verbatim. The first resembles the macro definition in theprevious structure. The second makes use of<code>\dostartbuffer[</code><i>name</i><code>][</code><i>bufferstart</i><code>][<i>bufferstop</i><code>]</code>, which creates a pair of buffer commands that write their contents verbatim to a named buffer. This buffer can then be accessed in LuaTeX via <code>buffers.content(</code><i>name</i><code>)</code>. Examples of both are provided below.text ==
<!--''This example demonstrates defining a custom {{cmd|start}}…{{cmd|stop}} buffer that gets processed through Lua in its entirety.''[[Inside_ConTeXt#Passing_verbatim_text_as_macro_parameterSuppose we want to write an environment {{cmd|startdedentedtyping}} … {{cmd|Inside Context]] article on this wikistopdedentedtyping}} that removes the indentation of the first line from every line. LuckilyThus, however, ConTeXt provides the -->output of …
First, a definition using the two-macro pattern seen above. The cleaner named-buffer pattern is below.
% This code, too, is due to Wolfgang Schuster on the ntg-ConTeXt mailing list.\unprotectstartdedentedtyping \def\startDedentA#include <stdio.h> {\begingroup \obeylines\obeyspaces% \dostartDedentA} void main() \def\dostartDedentA#1\stopDedentA{ {\ctxlua{thirddata.dedentprint("Hello world \!!bs\normalunexpanded{#1}\!!esn")}%; \endgroup }\protect % Try it out:\starttext \startDedentA andra moi ennepe \stopDedentA\stoptextstopdedentedtyping
%% Define a buffer \startDedentA ... \stopDedentB that feeds its contents%% to LuaTex for processing.starttyping% Tell TeX what strings the dedentBuffer starts and ends with#include <stdio.h>\def\startDedentB {\dostartbuffer[dedentBuffer][startDedentB][stopDedentB]}% Make the ending command void main(which will also signal the buffer's end)% call LuaTeX to read out the buffer and dedent its contents.\def\stopDedentB{ {\directlua{ local code = buffers.contentprint("dedentbufferHello world \n"); thirddata.dedent(buffers.content(code))}} % Try it out:\starttext \startDedentB andra moi ennepe \stopDedentB\stoptextstoptyping
Don't worry about this code re-using Defining an environment in TeX that removes the same named buffer each time: eachleading spaces but leaves<code>\stopDedentB</code> immediately uses other spaces untouched is complicated. On the other hand, once we capture the <code>dedentBuffer</code>'s contentsof the environment, and each <code>\startDedentB</code> flushes removing the bufferleading indent or ''dedenting''s contents, so you can use as many <code>\startDedentB</code> blocks as you wantthecontent in Lua is easy. Here is a Lua function that uses simple stringsubstitutions.
= Parsing input without exploding your head =
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% function userdata.dedentedtyping(content) local lines = string.splitlines(content) local indent {\ifvoid\chemlowbox \high{{\switchtobodyfont= string.match(lines[small1], '^ +') or '' local pattern = '^' .. indent for i=1,#1}}% \else lines do \lohi{\box\chemlowbox} {{\switchtobodyfontlines[i] = string.gsub(lines[smalli]#1}},pattern,"") \fi} end
\unexpanded\def\molecule% {\bgroup \catcode`\_=\active \uccode`\~=`\_ \uppercase{\let~\chemlow}% \catcode`\^=\active \uccode`\~=`\^ \uppercase{\let~\chemhigh}% \dostepwiserecurse {65}{90}{1} {\catcode \recurselevel = \active \uccode`\~=\recurselevel \uppercase{\edef~{\noexpand\finishchem \rawcharacter{\recurselevel}}}}% tex.sprint("\catcode`\-=starttyping\active n" .. content .. "\uccode`\~=`\- \uppercase{\def~{--}}% stoptyping\domolecule }% n")
This monstrosity Here is a typical TeX parser. Appropriate characters need to be made active; occasionally, <code>\lccode</code> and <code>\uccode</the code> need to be set; signaling tricks are needed (for instance, checking if <code>\chemlowbox</code> is void); and then magic happens (or so it seems to a flabbergasted user). More sophisticated parsers involve creating finite state automata, which look even more monstrous. With luaTeX, things are different. luaTeX includes a general parser based on PEG (parsing expression grammar) called [httpdefining the {{cmd|startdedentedtyping}} … {{cmd|stopdedentedtyping}} pair://www.inf.puc-rio.br/roberto/lpeg/lpeg.html lpeg]. This makes writing parsers in TeX much more comprehensible. For example, the above <code>\molecule</code> macro can be written as
local lowercase = lpeg.R("az")local uppercase = lpeg.R("AZ")local backslash = lpeg.P("\\")% On closing the dedentedtyping environment, call the LuaTeXlocal csname = backslash * lpeg.P% function dedentedtyping(1) , and pass it the contents of * (1-backslash)^0% the buffer called 'dedentedtyping'local plus = lpeg.P("+") / "\def\textplus "stopdedentedtypinglocal minus = lpeg.P("-") / "\\textminus "local digit = lpeg.R("09")local sign = plus + minuslocal cardinal = digit^1local integer = sign^0 * cardinallocal leftbrace = lpeg.P("{")local rightbrace = lpeg.P("}")\ctxlualocal nobrace = 1 - (leftbrace + rightbrace)local nested = lpeg{userdata.P {leftbrace * dedentedtyping(csname + sign + nobrace + lpegbuffers.Vgetcontent(1'dedentedtyping'))^0 * rightbrace}}local any = lpeg.P(1) local subscript = lpeg.P("_")local superscript = lpeg.P("^")local somescript = subscript + superscript local content = lpeg.Cs(csname + nested + sign + any)</texcode>
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{%That's}") * superscript * content / stringall.formatlocal justtext = (1 - somescript)^1local parser = lpegFinally, we will go into a little more detail on how TeX and Lua communicate with each other.Cs((csname + lowhigh + highlow + low + high + sign + any)^0)
userdata.moleculeparser = parser = Other examples ==
function userdata.molecule* [[Calculations_in_Lua|Calculations in Lua]] (strwarning date 2012) return * [[LPeg|Writing a parser:matchwith LPeg]] (strLua Parsing Expression Grammars)end* [[Random|Random numbers]] in ConTeXt and MetaPost\stopluacode* [[SQL|An example with SQL database]]* [[Pascal's Triangle]]
\def\molecule#1% {\ctxlua{userdata.molecule("#1")}}</texcode> = In detail: the interaction between TeX and Lua =
This To a first approximation, the interaction between TeX and Lua is more verbose than straightforward. When TeX (i.e., the LuaTeX engine) starts, it loads the input file in memory and processes it token by token. When TeX solutionencounters {{cmd|directlua}}, it stops reading the file in memory, but is easier <em>fully expands the argument of {{cmd|directlua}}</em>, and passes the control to read and writea Lua instance. With The Lua instance, which runs with a proper parserfew preloaded libraries, I do not have to use tricks to check if either one or both 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> and is just like the Lua function <code>^print(…)</code> are presentexcept that <code>tex. More importantly, anyone print(once they know …)</code> prints to a <em>TeX stream</em> rather than to the lpeg syntax) can read standard output. When the parser and easily understand what Lua instance finishes processing its input, it doespasses the contents of the <em>TeX stream</em> back to TeX. This <ref>The output of <code>tex.print(…)</code> is in contrast buffered and not passed to TeX until the implementation based on Lua instance has stopped.</ref> TeX macro jugglery which require you to implement a 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 interpreter in your head to understandencounters another {{cmd|directlua{{cmd|, the above process is repeated.
= Conclusion =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 {{cmd|directlua}} is tricky. The above was a contrived example; if you ever need to escape quotes, you can use the {{cmd|startluacode}}…{{cmd|\stopluacode{{cmd| syntax.</ref>
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 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…)
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. <blockquote>The main thing about Lua code in a TeX document is this: the code is expanded by TeX ''before'' Lua gets to it. '''This means that all the Lua code, even the comments, must be valid TeX!''' A string like {{cmd|undefined}} will cause an immediate failure.</blockquote> = Introduction =Calling a bit of Lua inline: {{cmd|ctxlua}} == The command {{cmd|ctxlua}} is for short inline snippets of Lua, suchas
<texcode>
</texcode>
<texcode>
\def\DIVIDE#1#2ctxlua {-- A Lua comment tex.print("This is not printed")}\directluactxlua {% A Tex comment tex.print(#1/#2"This is printed")}}
</texcode>
<texcode>
\directlua%startluacode {tex-- include the file my-lua-lib.printluarequire("Depth 1 my-lua-lib") \\directlua{tex.print('Depth 2')}")}stopluacode
</texcode>
<texcode>
\ctxluastartluacode -- 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() -- A lua commentdo stuff end\stopluacode</texcode> The full list of canonical namespaces, taken from [https://distribution.contextgarden.net/current/context/latest/tex/context/base/mkxl/luat-ini.lmt luat-ini.printlmt]: <code><pre>userdata = userdata or { } -- for users ("This 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 not printed"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</pre></code> == Undefined Commands in Lua Comments == Lua code invoked inside TeX doesn’t allow TeX undefined commands ''even inside comments''. <texcode>\starttext\startluacode--\undefinedcommandfromme\stopluacodeHello\ctxlua{--\undefinedcommandfromme}\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>
<texcode>
\startusercode math.randomseed( global.os.time() ) function random(...)startluacode global.context(arg[math.random(1, #arg)]) end\stopusercodeuserdata = 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. === 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>
<texcode>
\startluacode
\starttext
\DedentOnemolecule{ andra moi ennepeHg^+}, \molecule{SO_4^{2-}}
\stoptext
</texcode>
<texcode>
</texcode>
… should be the same as the output of …
<texcode>
</texcode>
… even though the leading whitespace is different.
<texcode>
\newbox\chemlowbox startluacode\def\chemlow#1% -- Initialize a userdata name space to keep our own functions in. -- That way, we won't interfere with anything ConTeXt keeps in {\setbox\chemlowbox-- the global name space. \hbox{ userdata = userdata or {\switchtobodyfont[small]#1}}}
content = table.concat(lines,'\def\finishchem% {\ifvoid\chemlowbox\else \low{\box\chemlowbox} \fi} n')
-- The typing environment looks for an explicit \deftype{\stoptyping}. So, -- context.starttyping() context(content) context.stoptyping() -- does not work. But -- context.starttyping() context(content) tex.sprint("\domolecule#1{#1\finishchemstoptyping") -- does. end\egroup}stopluacode
</texcode>
<texcode>
% Create an environment that stores everything % between \startdedentedtyping and \stopdedentedtyping % in a buffer named 'dedentedtyping'.\def\startluacodestartdedentedtypinguserdata = userdata or {\dostartbuffer [dedentedtyping] [startdedentedtyping] [stopdedentedtyping]}
= 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]]
