Scintillua API Documentation


  1. Scintillua
  2. lexer



The Scintillua Scintilla lexer has its own API to avoid any modifications to Scintilla itself. It is invoked using SCI_PRIVATELEXERCALL. Please note that some of the names of the API calls do not make perfect sense. This is a tradeoff in order to keep Scintilla unmodified.

The following notation is used:

SCI_PRIVATELEXERCALL (int operation, void *pointer)

This means you would call Scintilla like this:

SendScintilla(sci, SCI_PRIVATELEXERCALL, operation, pointer);

Scintillua Usage Example

Here is a pseudo-code example:

init_app() {
  sci = scintilla_new()
  lib = "/home/mitchell/app/lexers/"
  SendScintilla(sci, SCI_LOADLEXERLIBRARY, 0, lib)

create_doc() {
  doc = SendScintilla(sci, SCI_CREATEDOCUMENT)
  SendScintilla(sci, SCI_SETDOCPOINTER, 0, doc)
  SendScintilla(sci, SCI_SETLEXERLANGUAGE, 0, "lpeg")
  home = "/home/mitchell/app/lexers"
  SendScintilla(sci, SCI_SETPROPERTY, "lexer.lpeg.home", home)
  SendScintilla(sci, SCI_SETPROPERTY, "lexer.lpeg.color.theme", "light")
  fn = SendScintilla(sci, SCI_GETDIRECTFUNCTION)
  psci = SendScintilla(sci, SCI_GETDIRECTPOINTER)

set_lexer(lang) {
  psci = SendScintilla(sci, SCI_GETDIRECTPOINTER)

Functions defined by Scintillua


Tells Scintillua to use lua as its Lua state instead of creating a separate state.

lua must have already opened the “base”, “string”, “table”, “package”, and “lpeg” libraries. If lua is a Lua 5.1 state, it must have also opened the “io” library.

Scintillua will create a single lexer package (that can be used with Lua’s require()), as well as a number of other variables in the LUA_REGISTRYINDEX table with the “sci_” prefix.

Instead of including the path to Scintillua’s lexers in the package.path of the given Lua state, set the “lexer.lpeg.home” property appropriately instead. Scintillua uses that property to find and load lexers.




Tells Scintillua the address of the function that handles Scintilla messages.

Despite the name SCI_GETDIRECTFUNCTION, it only notifies Scintillua what the value of SciFnDirect obtained from SCI_GETDIRECTFUNCTION is. It does not return anything. Use this if you would like to have the Scintillua lexer set all Lua LPeg lexer styles automatically. This is useful for maintaining a consistent color theme. Do not use this if your application maintains its own color theme.

If you use this call, it must be made once for each Scintilla buffer that was created using SCI_CREATEDOCUMENT. You must also use the SCI_SETDOCPOINTER() Scintillua API call.



See also:


Returns the length of the string name of the current Lua LPeg lexer or stores the name into the given buffer. If the buffer is long enough, the name is terminated by a 0 character.

For parent lexers with embedded children or child lexers embedded into parents, the name is in “lexer/current” format, where “lexer” is the actual lexer’s name and “current” is the parent or child lexer at the current caret position. In order for this to work, you must have called SCI_GETDIRECTFUNCTION and SCI_SETDOCPOINTER.



Returns the error message of the Scintillua or Lua LPeg lexer error that occurred (if any).

If no error occurred, the returned message will be empty.

Since Scintillua does not throw errors as they occur, errors can only be handled passively. Note that Scintillua does print all errors to stderr.




Depending on the sign of styleNum, returns the length of the associated string for the given style number or stores the string into the given buffer. If the buffer is long enough, the string is terminated by a 0 character.

For negative styleNum, the associated string is a SciTE-formatted style definition. Otherwise, the associated string is the name of the token for the given style number.

Please see the SciTE documentation for the style definition format specified by style.*.stylenumber. You can parse these definitions to set Lua LPeg lexer styles manually if you chose not to have them set automatically using the SCI_GETDIRECTFUNCTION() and SCI_SETDOCPOINTER() Scintillua API calls.




Tells Scintillua the address of the Scintilla window currently in use.

Despite the name SCI_SETDOCPOINTER, it has no relationship to Scintilla documents.

Use this call only if you are using the SCI_GETDIRECTFUNCTION() Scintillua API call. It must be made before each call to the SCI_SETLEXERLANGUAGE() Scintillua API call.



See also:


Sets the current Lua LPeg lexer to languageName.

If you are having the Scintillua lexer set the Lua LPeg lexer styles automatically, make sure you call the SCI_SETDOCPOINTER() Scintillua API first.



See also:

The lexer Module

Lexes Scintilla documents with Lua and LPeg.


Lexers highlight the syntax of source code. Scintilla (the editing component behind Textadept and SciTE) traditionally uses static, compiled C++ lexers which are notoriously difficult to create and/or extend. On the other hand, Lua makes it easy to to rapidly create new lexers, extend existing ones, and embed lexers within one another. Lua lexers tend to be more readable than C++ lexers too.

Lexers are Parsing Expression Grammars, or PEGs, composed with the Lua LPeg library. The following table comes from the LPeg documentation and summarizes all you need to know about constructing basic LPeg patterns. This module provides convenience functions for creating and working with other more advanced patterns and concepts.

Operator Description
lpeg.P(string) Matches string literally.
lpeg.P(n) Matches exactly n characters.
lpeg.S(string) Matches any character in set string.
lpeg.R("xy") Matches any character between range x and y.
patt^n Matches at least n repetitions of patt.
patt^-n Matches at most n repetitions of patt.
patt1 * patt2 Matches patt1 followed by patt2.
patt1 + patt2 Matches patt1 or patt2 (ordered choice).
patt1 - patt2 Matches patt1 if patt2 does not match.
-patt Equivalent to ("" - patt).
#patt Matches patt but consumes no input.

The first part of this document deals with rapidly constructing a simple lexer. The next part deals with more advanced techniques, such as custom coloring and embedding lexers within one another. Following that is a discussion about code folding, or being able to tell Scintilla which code blocks are “foldable” (temporarily hideable from view). After that are instructions on how to use LPeg lexers with the aforementioned Textadept and SciTE editors. Finally there are comments on lexer performance and limitations.

Lexer Basics

The lexers/ directory contains all lexers, including your new one. Before attempting to write one from scratch though, first determine if your programming language is similar to any of the 80+ languages supported. If so, you may be able to copy and modify that lexer, saving some time and effort. The filename of your lexer should be the name of your programming language in lower case followed by a .lua extension. For example, a new Lua lexer has the name lua.lua.

Note: Try to refrain from using one-character language names like “c”, “d”, or “r”. For example, Scintillua uses “ansi_c”, “dmd”, and “rstats”, respectively.

New Lexer Template

There is a lexers/template.txt file that contains a simple template for a new lexer. Feel free to use it, replacing the ‘?’s with the name of your lexer:

-- ? LPeg lexer.

local l = require('lexer')
local token, word_match = l.token, l.word_match
local P, R, S = lpeg.P, lpeg.R, lpeg.S

local M = {_NAME = '?'}

-- Whitespace.
local ws = token(l.WHITESPACE,^1)

M._rules = {
  {'whitespace', ws},

M._tokenstyles = {


return M

The first 3 lines of code simply define often used convenience variables. The 5th and last lines define and return the lexer object Scintilla uses; they are very important and must be part of every lexer. The sixth line defines something called a “token”, an essential building block of lexers. You will learn about tokens shortly. The rest of the code defines a set of grammar rules and token styles. You will learn about those later. Note, however, the M. prefix in front of _rules and _tokenstyles: not only do these tables belong to their respective lexers, but any non-local variables need the M. prefix too so-as not to affect Lua’s global environment. All in all, this is a minimal, working lexer that you can build on.


Take a moment to think about your programming language’s structure. What kind of key elements does it have? In the template shown earlier, one predefined element all languages have is whitespace. Your language probably also has elements like comments, strings, and keywords. Lexers refer to these elements as “tokens”. Tokens are the fundamental “building blocks” of lexers. Lexers break down source code into tokens for coloring, which results in the syntax highlighting familiar to you. It is up to you how specific your lexer is when it comes to tokens. Perhaps only distinguishing between keywords and identifiers is necessary, or maybe recognizing constants and built-in functions, methods, or libraries is desirable. The Lua lexer, for example, defines 11 tokens: whitespace, comments, strings, numbers, keywords, built-in functions, constants, built-in libraries, identifiers, labels, and operators. Even though constants, built-in functions, and built-in libraries are subsets of identifiers, Lua programmers find it helpful for the lexer to distinguish between them all. It is perfectly acceptable to just recognize keywords and identifiers.

In a lexer, tokens consist of a token name and an LPeg pattern that matches a sequence of characters recognized as an instance of that token. Create tokens using the lexer.token() function. Let us examine the “whitespace” token defined in the template shown earlier:

local ws = token(l.WHITESPACE,^1)

At first glance, the first argument does not appear to be a string name and the second argument does not appear to be an LPeg pattern. Perhaps you expected something like:

local ws = token('whitespace', S('\t\v\f\n\r ')^1)

The lexer (l) module actually provides a convenient list of common token names and common LPeg patterns for you to use. Token names include lexer.DEFAULT, lexer.WHITESPACE, lexer.COMMENT, lexer.STRING, lexer.NUMBER, lexer.KEYWORD, lexer.IDENTIFIER, lexer.OPERATOR, lexer.ERROR, lexer.PREPROCESSOR, lexer.CONSTANT, lexer.VARIABLE, lexer.FUNCTION, lexer.CLASS, lexer.TYPE, lexer.LABEL, lexer.REGEX, and lexer.EMBEDDED. Patterns include lexer.any, lexer.ascii, lexer.extend, lexer.alpha, lexer.digit, lexer.alnum, lexer.lower, lexer.upper, lexer.xdigit, lexer.cntrl, lexer.graph, lexer.print, lexer.punct,, lexer.newline, lexer.nonnewline, lexer.nonnewline_esc, lexer.dec_num, lexer.hex_num, lexer.oct_num, lexer.integer, lexer.float, and lexer.word. You may use your own token names if none of the above fit your language, but an advantage to using predefined token names is that your lexer’s tokens will inherit the universal syntax highlighting color theme used by your text editor.

Example Tokens

So, how might you define other tokens like comments, strings, and keywords? Here are some examples.


Line-style comments with a prefix character(s) are easy to express with LPeg:

local shell_comment = token(l.COMMENT, '#' * l.nonnewline^0)
local c_line_comment = token(l.COMMENT, '//' * l.nonnewline_esc^0)

The comments above start with a ‘#’ or “//” and go to the end of the line. The second comment recognizes the next line also as a comment if the current line ends with a ‘\’ escape character.

C-style “block” comments with a start and end delimiter are also easy to express:

local c_comment = token(l.COMMENT, '/*' * (l.any - '*/')^0 * P('*/')^-1)

This comment starts with a “/*” sequence and contains anything up to and including an ending “*/” sequence. The ending “*/” is optional so the lexer can recognize unfinished comments as comments and highlight them properly.


It is tempting to think that a string is not much different from the block comment shown above in that both have start and end delimiters:

local dq_str = '"' * (l.any - '"')^0 * P('"')^-1
local sq_str = "'" * (l.any - "'")^0 * P("'")^-1
local simple_string = token(l.STRING, dq_str + sq_str)

However, most programming languages allow escape sequences in strings such that a sequence like “\"” in a double-quoted string indicates that the ‘"’ is not the end of the string. The above token incorrectly matches such a string. Instead, use the lexer.delimited_range() convenience function.

local dq_str = l.delimited_range('"')
local sq_str = l.delimited_range("'")
local string = token(l.STRING, dq_str + sq_str)

In this case, the lexer treats ‘\’ as an escape character in a string sequence.


Instead of matching n keywords with n P('keyword_n') ordered choices, use another convenience function: lexer.word_match(). It is much easier and more efficient to write word matches like:

local keyword = token(l.KEYWORD, l.word_match{
  'keyword_1', 'keyword_2', ..., 'keyword_n'

local case_insensitive_keyword = token(l.KEYWORD, l.word_match({
  'KEYWORD_1', 'keyword_2', ..., 'KEYword_n'
}, nil, true))

local hyphened_keyword = token(l.KEYWORD, l.word_match({
  'keyword-1', 'keyword-2', ..., 'keyword-n'
}, '-'))

By default, characters considered to be in keywords are in the set of alphanumeric characters and underscores. The last token demonstrates how to allow ‘-’ (hyphen) characters to be in keywords as well.


Most programming languages have the same format for integer and float tokens, so it might be as simple as using a couple of predefined LPeg patterns:

local number = token(l.NUMBER, l.float + l.integer)

However, some languages allow postfix characters on integers.

local integer = P('-')^-1 * (l.dec_num * S('lL')^-1)
local number = token(l.NUMBER, l.float + l.hex_num + integer)

Your language may need other tweaks, but it is up to you how fine-grained you want your highlighting to be. After all, you are not writing a compiler or interpreter!


Programming languages have grammars, which specify valid token structure. For example, comments usually cannot appear within a string. Grammars consist of rules, which are simply combinations of tokens. Recall from the lexer template the _rules table, which defines all the rules used by the lexer grammar:

M._rules = {
  {'whitespace', ws},

Each entry in a lexer’s _rules table consists of a rule name and its associated pattern. Rule names are completely arbitrary and serve only to identify and distinguish between different rules. Rule order is important: if text does not match the first rule, the lexer tries the second rule, and so on. This simple grammar says to match whitespace tokens under a rule named “whitespace”.

To illustrate the importance of rule order, here is an example of a simplified Lua grammar:

M._rules = {
  {'whitespace', ws},
  {'keyword', keyword},
  {'identifier', identifier},
  {'string', string},
  {'comment', comment},
  {'number', number},
  {'label', label},
  {'operator', operator},

Note how identifiers come after keywords. In Lua, as with most programming languages, the characters allowed in keywords and identifiers are in the same set (alphanumerics plus underscores). If the lexer specified the “identifier” rule before the “keyword” rule, all keywords would match identifiers and thus incorrectly highlight as identifiers instead of keywords. The same idea applies to function, constant, etc. tokens that you may want to distinguish between: their rules should come before identifiers.

So what about text that does not match any rules? For example in Lua, the ‘!’ character is meaningless outside a string or comment. Normally the lexer skips over such text. If instead you want to highlight these “syntax errors”, add an additional end rule:

M._rules = {
  {'whitespace', ws},
  {'error', token(l.ERROR, l.any)},

This identifies and highlights any character not matched by an existing rule as an lexer.ERROR token.

Even though the rules defined in the examples above contain a single token, rules may consist of multiple tokens. For example, a rule for an HTML tag could consist of a tag token followed by an arbitrary number of attribute tokens, allowing the lexer to highlight all tokens separately. The rule might look something like this:

{'tag', tag_start * (ws * attributes)^0 * tag_end^-1}

Note however that lexers with complex rules like these are more prone to lose track of their state.


Lexers primarily consist of tokens and grammar rules. At your disposal are a number of convenience patterns and functions for rapidly creating a lexer. If you choose to use predefined token names for your tokens, you do not have to define how the lexer highlights them. The tokens will inherit the default syntax highlighting color theme your editor uses.

Advanced Techniques

Styles and Styling

The most basic form of syntax highlighting is assigning different colors to different tokens. Instead of highlighting with just colors, Scintilla allows for more rich highlighting, or “styling”, with different fonts, font sizes, font attributes, and foreground and background colors, just to name a few. The unit of this rich highlighting is called a “style”. Styles are simply strings of comma-separated property settings. By default, lexers associate predefined token names like lexer.WHITESPACE, lexer.COMMENT, lexer.STRING, etc. with particular styles as part of a universal color theme. These predefined styles include lexer.STYLE_CLASS, lexer.STYLE_COMMENT, lexer.STYLE_CONSTANT, lexer.STYLE_ERROR, lexer.STYLE_EMBEDDED, lexer.STYLE_FUNCTION, lexer.STYLE_IDENTIFIER, lexer.STYLE_KEYWORD, lexer.STYLE_LABEL, lexer.STYLE_NUMBER, lexer.STYLE_OPERATOR, lexer.STYLE_PREPROCESSOR, lexer.STYLE_REGEX, lexer.STYLE_STRING, lexer.STYLE_TYPE, lexer.STYLE_VARIABLE, and lexer.STYLE_WHITESPACE. Like with predefined token names and LPeg patterns, you may define your own styles. At their core, styles are just strings, so you may create new ones and/or modify existing ones. Each style consists of the following comma-separated settings:

Setting Description
font:name The name of the font the style uses.
size:int The size of the font the style uses.
[not]bold Whether or not the font face is bold.
weight:int The weight or boldness of a font, between 1 and 999.
[not]italics Whether or not the font face is italic.
[not]underlined Whether or not the font face is underlined.
fore:color The foreground color of the font face.
back:color The background color of the font face.
[not]eolfilled Does the background color extend to the end of the line?
case:char The case of the font (‘u’: upper, ‘l’: lower, ’m': normal).
[not]visible Whether or not the text is visible.
[not]changeable Whether the text is changeable or read-only.

Specify font colors in either “#RRGGBB” format, “0xBBGGRR” format, or the decimal equivalent of the latter. As with token names, LPeg patterns, and styles, there is a set of predefined color names, but they vary depending on the current color theme in use. Therefore, it is generally not a good idea to manually define colors within styles in your lexer since they might not fit into a user’s chosen color theme. Try to refrain from even using predefined colors in a style because that color may be theme-specific. Instead, the best practice is to either use predefined styles or derive new color-agnostic styles from predefined ones. For example, Lua “longstring” tokens use the existing lexer.STYLE_STRING style instead of defining a new one.

Example Styles

Defining styles is pretty straightforward. An empty style that inherits the default theme settings is simply an empty string:

local style_nothing = ''

A similar style but with a bold font face looks like this:

local style_bold = 'bold'

If you want the same style, but also with an italic font face, define the new style in terms of the old one:

local style_bold_italic = style_bold..',italics'

This allows you to derive new styles from predefined ones without having to rewrite them. This operation leaves the old style unchanged. Thus if you had a “static variable” token whose style you wanted to base off of lexer.STYLE_VARIABLE, it would probably look like:

local style_static_var = l.STYLE_VARIABLE..',italics'

The color theme files in the lexers/themes/ folder give more examples of style definitions.

Token Styles

Lexers use the _tokenstyles table to assign tokens to particular styles. Recall the token definition and _tokenstyles table from the lexer template:

local ws = token(l.WHITESPACE,^1)


M._tokenstyles = {


Why is a style not assigned to the lexer.WHITESPACE token? As mentioned earlier, lexers automatically associate tokens that use predefined token names with a particular style. Only tokens with custom token names need manual style associations. As an example, consider a custom whitespace token:

local ws = token('custom_whitespace',^1)

Assigning a style to this token looks like:

M._tokenstyles = {
  custom_whitespace = l.STYLE_WHITESPACE

Do not confuse token names with rule names. They are completely different entities. In the example above, the lexer assigns the “custom_whitespace” token the existing style for WHITESPACE tokens. If instead you want to color the background of whitespace a shade of grey, it might look like:

local custom_style = l.STYLE_WHITESPACE..',back:$(color.grey)'
M._tokenstyles = {
  custom_whitespace = custom_style

Notice that the lexer peforms Scintilla/SciTE-style “$()” property expansion. You may also use “%()”. Remember to refrain from assigning specific colors in styles, but in this case, all user color themes probably define the “color.grey” property.

Line Lexers

By default, lexers match the arbitrary chunks of text passed to them by Scintilla. These chunks may be a full document, only the visible part of a document, or even just portions of lines. Some lexers need to match whole lines. For example, a lexer for the output of a file “diff” needs to know if the line started with a ‘+’ or ‘-’ and then style the entire line accordingly. To indicate that your lexer matches by line, use the _LEXBYLINE field:


Now the input text for the lexer is a single line at a time. Keep in mind that line lexers do not have the ability to look ahead at subsequent lines.

Embedded Lexers

Lexers embed within one another very easily, requiring minimal effort. In the following sections, the lexer being embedded is called the “child” lexer and the lexer a child is being embedded in is called the “parent”. For example, consider an HTML lexer and a CSS lexer. Either lexer stands alone for styling their respective HTML and CSS files. However, CSS can be embedded inside HTML. In this specific case, the CSS lexer is the “child” lexer with the HTML lexer being the “parent”. Now consider an HTML lexer and a PHP lexer. This sounds a lot like the case with CSS, but there is a subtle difference: PHP embeds itself into HTML while CSS is embedded in HTML. This fundamental difference results in two types of embedded lexers: a parent lexer that embeds other child lexers in it (like HTML embedding CSS), and a child lexer that embeds itself within a parent lexer (like PHP embedding itself in HTML).

Parent Lexer

Before embedding a child lexer into a parent lexer, the parent lexer needs to load the child lexer. This is done with the lexer.load() function. For example, loading the CSS lexer within the HTML lexer looks like:

local css = l.load('css')

The next part of the embedding process is telling the parent lexer when to switch over to the child lexer and when to switch back. The lexer refers to these indications as the “start rule” and “end rule”, respectively, and are just LPeg patterns. Continuing with the HTML/CSS example, the transition from HTML to CSS is when the lexer encounters a “style” tag with a “type” attribute whose value is “text/css”:

local css_tag = P('<style') * P(function(input, index)
  if input:find('^[^>]+type="text/css"', index) then
    return index

This pattern looks for the beginning of a “style” tag and searches its attribute list for the text “type="text/css"”. (In this simplified example, the Lua pattern does not consider whitespace between the ‘=’ nor does it consider that using single quotes is valid.) If there is a match, the functional pattern returns a value instead of nil. In this case, the value returned does not matter because we ultimately want to style the “style” tag as an HTML tag, so the actual start rule looks like this:

local css_start_rule = #css_tag * tag

Now that the parent knows when to switch to the child, it needs to know when to switch back. In the case of HTML/CSS, the switch back occurs when the lexer encounters an ending “style” tag, though the lexer should still style the tag as an HTML tag:

local css_end_rule = #P('</style>') * tag

Once the parent loads the child lexer and defines the child’s start and end rules, it embeds the child with the lexer.embed_lexer() function:

l.embed_lexer(M, css, css_start_rule, css_end_rule)

The first parameter is the parent lexer object to embed the child in, which in this case is M. The other three parameters are the child lexer object loaded earlier followed by its start and end rules.

Child Lexer

The process for instructing a child lexer to embed itself into a parent is very similar to embedding a child into a parent: first, load the parent lexer into the child lexer with the lexer.load() function and then create start and end rules for the child lexer. However, in this case, swap the lexer object arguments to lexer.embed_lexer(). For example, in the PHP lexer:

local html = l.load('html')
local php_start_rule = token('php_tag', '<?php ')
local php_end_rule = token('php_tag', '?>')
l.embed_lexer(html, M, php_start_rule, php_end_rule)

Lexers with Complex State

A vast majority of lexers are not stateful and can operate on any chunk of text in a document. However, there may be rare cases where a lexer does need to keep track of some sort of persistent state. Rather than using lpeg.P function patterns that set state variables, it is recommended to make use of Scintilla’s built-in, per-line state integers via lexer.line_state. It was designed to accommodate up to 32 bit flags for tracking state. lexer.line_from_position() will return the line for any position given to an lpeg.P function pattern. (Any positions derived from that position argument will also work.)

Writing stateful lexers is beyond the scope of this document.

Code Folding

When reading source code, it is occasionally helpful to temporarily hide blocks of code like functions, classes, comments, etc. This is the concept of “folding”. In the Textadept and SciTE editors for example, little indicators in the editor margins appear next to code that can be folded at places called “fold points”. When the user clicks an indicator, the editor hides the code associated with the indicator until the user clicks the indicator again. The lexer specifies these fold points and what code exactly to fold.

The fold points for most languages occur on keywords or character sequences. Examples of fold keywords are “if” and “end” in Lua and examples of fold character sequences are ‘{’, ‘}’, “/*”, and “*/” in C for code block and comment delimiters, respectively. However, these fold points cannot occur just anywhere. For example, lexers should not recognize fold keywords that appear within strings or comments. The lexer’s _foldsymbols table allows you to conveniently define fold points with such granularity. For example, consider C:

M._foldsymbols = {
  [l.OPERATOR] = {['{'] = 1, ['}'] = -1},
  [l.COMMENT] = {['/*'] = 1, ['*/'] = -1},
  _patterns = {'[{}]', '/%*', '%*/'}

The first assignment states that any ‘{’ or ‘}’ that the lexer recognized as an lexer.OPERATOR token is a fold point. The integer 1 indicates the match is a beginning fold point and -1 indicates the match is an ending fold point. Likewise, the second assignment states that any “/*” or “*/” that the lexer recognizes as part of a lexer.COMMENT token is a fold point. The lexer does not consider any occurences of these characters outside their defined tokens (such as in a string) as fold points. Finally, every _foldsymbols table must have a _patterns field that contains a list of Lua patterns that match fold points. If the lexer encounters text that matches one of those patterns, the lexer looks up the matched text in its token’s table in order to determine whether or not the text is a fold point. In the example above, the first Lua pattern matches any ‘{’ or ‘}’ characters. When the lexer comes across one of those characters, it checks if the match is an lexer.OPERATOR token. If so, the lexer identifies the match as a fold point. The same idea applies for the other patterns. (The ‘%’ is in the other patterns because ‘*’ is a special character in Lua patterns that needs escaping.) How do you specify fold keywords? Here is an example for Lua:

M._foldsymbols = {
  [l.KEYWORD] = {
    ['if'] = 1, ['do'] = 1, ['function'] = 1,
    ['end'] = -1, ['repeat'] = 1, ['until'] = -1
  _patterns = {'%l+'}

Any time the lexer encounters a lower case word, if that word is a lexer.KEYWORD token and in the associated list of fold points, the lexer identifies the word as a fold point.

If your lexer has case-insensitive keywords as fold points, simply add a _case_insensitive = true option to the _foldsymbols table and specify keywords in lower case.

If your lexer needs to do some additional processing to determine if a match is a fold point, assign a function that returns an integer. Returning 1 or -1 indicates the match is a fold point. Returning 0 indicates it is not. For example:

local function fold_strange_token(text, pos, line, s, match)
  if ... then
    return 1 -- beginning fold point
  elseif ... then
    return -1 -- ending fold point
  return 0

M._foldsymbols = {
  ['strange_token'] = {['|'] = fold_strange_token},
  _patterns = {'|'}

Any time the lexer encounters a ‘|’ that is a “strange_token”, it calls the fold_strange_token function to determine if ‘|’ is a fold point. The lexer calls these functions with the following arguments: the text to identify fold points in, the beginning position of the current line in the text to fold, the current line’s text, the position in the current line the matched text starts at, and the matched text itself.

Fold by Indentation

Some languages have significant whitespace and/or no delimiters that indicate fold points. If your lexer falls into this category and you would like to mark fold points based on changes in indentation, use the _FOLDBYINDENTATION field:


Using Lexers


Put your lexer in your ~/.textadept/lexers/ directory so you do not overwrite it when upgrading Textadept. Also, lexers in this directory override default lexers. Thus, Textadept loads a user lua lexer instead of the default lua lexer. This is convenient for tweaking a default lexer to your liking. Then add a file type for your lexer if necessary.


Create a .properties file for your lexer and import it in either your or The contents of the .properties file should contain:


where [lexer_name] is the name of your lexer (minus the .lua extension) and [file_patterns] is a set of file extensions to use your lexer for.

Please note that Lua lexers ignore any styling information in .properties files. Your theme file in the lexers/themes/ directory contains styling information.



There might be some slight overhead when initializing a lexer, but loading a file from disk into Scintilla is usually more expensive. On modern computer systems, I see no difference in speed between LPeg lexers and Scintilla’s C++ ones. Optimize lexers for speed by re-arranging rules in the _rules table so that the most common rules match first. Do keep in mind that order matters for similar rules.


Embedded preprocessor languages like PHP cannot completely embed in their parent languages in that the parent’s tokens do not support start and end rules. This mostly goes unnoticed, but code like

<div id="<?php echo $id; ?>">


<div <?php if ($odd) { echo 'class="odd"'; } ?>>

will not style correctly.


Errors in lexers can be tricky to debug. Lexers print Lua errors to io.stderr and _G.print() statements to io.stdout. Running your editor from a terminal is the easiest way to see errors as they occur.


Poorly written lexers have the ability to crash Scintilla (and thus its containing application), so unsaved data might be lost. However, I have only observed these crashes in early lexer development, when syntax errors or pattern errors are present. Once the lexer actually starts styling text (either correctly or incorrectly, it does not matter), I have not observed any crashes.


Thanks to Peter Odding for his lexer post on the Lua mailing list that inspired me, and thanks to Roberto Ierusalimschy for LPeg.

Fields defined by lexer

lexer.CLASS (string)

The token name for class tokens.

lexer.COMMENT (string)

The token name for comment tokens.

lexer.CONSTANT (string)

The token name for constant tokens.

lexer.DEFAULT (string)

The token name for default tokens.

lexer.ERROR (string)

The token name for error tokens.

lexer.FOLD_BASE (number)

The initial (root) fold level.

lexer.FOLD_BLANK (number)

Flag indicating that the line is blank.

lexer.FOLD_HEADER (number)

Flag indicating the line is fold point.

lexer.FUNCTION (string)

The token name for function tokens.

lexer.IDENTIFIER (string)

The token name for identifier tokens.

lexer.KEYWORD (string)

The token name for keyword tokens.

lexer.LABEL (string)

The token name for label tokens.

lexer.LEXERPATH (string)

The path used to search for a lexer to load. Identical in format to Lua’s package.path string. The default value is package.path.

lexer.NUMBER (string)

The token name for number tokens.

lexer.OPERATOR (string)

The token name for operator tokens.

lexer.PREPROCESSOR (string)

The token name for preprocessor tokens.

lexer.REGEX (string)

The token name for regex tokens.

lexer.STRING (string)

The token name for string tokens.

lexer.STYLE_BRACEBAD (string)

The style used for unmatched brace characters.

lexer.STYLE_BRACELIGHT (string)

The style used for highlighted brace characters.

lexer.STYLE_CALLTIP (string)

The style used by call tips if buffer.call_tip_use_style is set. Only the font name, size, and color attributes are used.

lexer.STYLE_CLASS (string)

The style typically used for class definitions.

lexer.STYLE_COMMENT (string)

The style typically used for code comments.

lexer.STYLE_CONSTANT (string)

The style typically used for constants.

lexer.STYLE_CONTROLCHAR (string)

The style used for control characters. Color attributes are ignored.

lexer.STYLE_DEFAULT (string)

The style all styles are based off of.

lexer.STYLE_EMBEDDED (string)

The style typically used for embedded code.

lexer.STYLE_ERROR (string)

The style typically used for erroneous syntax.


The style used for fold display text.

lexer.STYLE_FUNCTION (string)

The style typically used for function definitions.

lexer.STYLE_IDENTIFIER (string)

The style typically used for identifier words.

lexer.STYLE_INDENTGUIDE (string)

The style used for indentation guides.

lexer.STYLE_KEYWORD (string)

The style typically used for language keywords.

lexer.STYLE_LABEL (string)

The style typically used for labels.

lexer.STYLE_LINENUMBER (string)

The style used for all margins except fold margins.

lexer.STYLE_NUMBER (string)

The style typically used for numbers.

lexer.STYLE_OPERATOR (string)

The style typically used for operators.


The style typically used for preprocessor statements.

lexer.STYLE_REGEX (string)

The style typically used for regular expression strings.

lexer.STYLE_STRING (string)

The style typically used for strings.

lexer.STYLE_TYPE (string)

The style typically used for static types.

lexer.STYLE_VARIABLE (string)

The style typically used for variables.

lexer.STYLE_WHITESPACE (string)

The style typically used for whitespace.

lexer.TYPE (string)

The token name for type tokens.

lexer.VARIABLE (string)

The token name for variable tokens.

lexer.WHITESPACE (string)

The token name for whitespace tokens.

lexer.alnum (pattern)

A pattern that matches any alphanumeric character (‘A’-‘Z’, ‘a’-‘z’, ‘0’-‘9’).

lexer.alpha (pattern)

A pattern that matches any alphabetic character (‘A’-‘Z’, ‘a’-‘z’).

lexer.any (pattern)

A pattern that matches any single character.

lexer.ascii (pattern)

A pattern that matches any ASCII character (codes 0 to 127).

lexer.cntrl (pattern)

A pattern that matches any control character (ASCII codes 0 to 31).

lexer.dec_num (pattern)

A pattern that matches a decimal number.

lexer.digit (pattern)

A pattern that matches any digit (‘0’-‘9’).

lexer.extend (pattern)

A pattern that matches any ASCII extended character (codes 0 to 255).

lexer.float (pattern)

A pattern that matches a floating point number.

lexer.fold_level (table, Read-only)

Table of fold level bit-masks for line numbers starting from zero. Fold level masks are composed of an integer level combined with any of the following bits:

lexer.graph (pattern)

A pattern that matches any graphical character (‘!’ to ‘~’).

lexer.hex_num (pattern)

A pattern that matches a hexadecimal number.

lexer.indent_amount (table, Read-only)

Table of indentation amounts in character columns, for line numbers starting from zero.

lexer.integer (pattern)

A pattern that matches either a decimal, hexadecimal, or octal number.

lexer.line_state (table)

Table of integer line states for line numbers starting from zero. Line states can be used by lexers for keeping track of persistent states.

lexer.lower (pattern)

A pattern that matches any lower case character (‘a’-‘z’).

lexer.newline (pattern)

A pattern that matches any set of end of line characters.

lexer.nonnewline (pattern)

A pattern that matches any single, non-newline character.

lexer.nonnewline_esc (pattern)

A pattern that matches any single, non-newline character or any set of end of line characters escaped with ‘\’.

lexer.oct_num (pattern)

A pattern that matches an octal number.

lexer.print (pattern)

A pattern that matches any printable character (‘ ’ to ‘~’). (table)

Map of key-value string pairs.

lexer.property_expanded (table, Read-only)

Map of key-value string pairs with $() and %() variable replacement performed in values.

lexer.property_int (table, Read-only)

Map of key-value pairs with values interpreted as numbers, or 0 if not found.

lexer.punct (pattern)

A pattern that matches any punctuation character (‘!’ to ‘/’, ‘:’ to ‘@’, ‘[’ to ‘’‘, ’{‘ to ’~‘). (pattern)

A pattern that matches any whitespace character (‘\t’, ‘\v’, ‘\f’, ‘\n’, ‘\r’, space).

lexer.style_at (table, Read-only)

Table of style names at positions in the buffer starting from 1.

lexer.upper (pattern)

A pattern that matches any upper case character (‘A’-‘Z’).

lexer.word (pattern)

A pattern that matches a typical word. Words begin with a letter or underscore and consist of alphanumeric and underscore characters.

lexer.xdigit (pattern)

A pattern that matches any hexadecimal digit (‘0’-‘9’, ‘A’-‘F’, ‘a’-‘f’).

Functions defined by lexer

lexer.delimited_range (chars, single_line, no_escape, balanced)

Creates and returns a pattern that matches a range of text bounded by chars characters. This is a convenience function for matching more complicated delimited ranges like strings with escape characters and balanced parentheses. single_line indicates whether or not the range must be on a single line, no_escape indicates whether or not to ignore ‘\’ as an escape character, and balanced indicates whether or not to handle balanced ranges like parentheses and requires chars to be composed of two characters.




See also:

lexer.embed_lexer (parent, child, start_rule, end_rule)

Embeds child lexer child in parent lexer parent using patterns start_rule and end_rule, which signal the beginning and end of the embedded lexer, respectively.



lexer.fold (lexer, text, start_pos, start_line, start_level)

Determines fold points in a chunk of text text with lexer lexer. text starts at position start_pos on line number start_line with a beginning fold level of start_level in the buffer. If lexer has a _fold function or a _foldsymbols table, that field is used to perform folding. Otherwise, if lexer has a _FOLDBYINDENTATION field set, or if a property is set, folding by indentation is done.



lexer.fold_line_comments (prefix)

Returns a fold function (to be used within the lexer’s _foldsymbols table) that folds consecutive line comments that start with string prefix.



lexer.last_char_includes (s)

Creates and returns a pattern that verifies that string set s contains the first non-whitespace character behind the current match position.




lexer.lex (lexer, text, init_style)

Lexes a chunk of text text (that has an initial style number of init_style) with lexer lexer. If lexer has a _LEXBYLINE flag set, the text is lexed one line at a time. Otherwise the text is lexed as a whole.



lexer.line_from_position (pos)

Returns the line number of the line that contains position pos, which starts from 1.



lexer.load (name, alt_name)

Initializes or loads and returns the lexer of string name name. Scintilla calls this function in order to load a lexer. Parent lexers also call this function in order to load child lexers and vice-versa. The user calls this function in order to load a lexer when using Scintillua as a Lua library.



lexer.nested_pair (start_chars, end_chars)

Returns a pattern that matches a balanced range of text that starts with string start_chars and ends with string end_chars. With single-character delimiters, this function is identical to delimited_range(start_chars..end_chars, false, true, true).




See also:

lexer.starts_line (patt)

Creates and returns a pattern that matches pattern patt only at the beginning of a line.




lexer.token (name, patt)

Creates and returns a token pattern with token name name and pattern patt. If name is not a predefined token name, its style must be defined in the lexer’s _tokenstyles table.




lexer.word_match (words, word_chars, case_insensitive)

Creates and returns a pattern that matches any single word in list words. Words consist of alphanumeric and underscore characters, as well as the characters in string set word_chars. case_insensitive indicates whether or not to ignore case when matching words. This is a convenience function for simplifying a set of ordered choice word patterns.




Tables defined by lexer


Individual fields for a lexer instance.