| Scintilla

# Lua LPeg Lexers

Scintilla's LPeg lexer adds dynamic Lua LPeg lexers to Scintilla. It is the quickest way to add new or customized syntax highlighting and code folding for programming languages to any Scintilla-based text editor or IDE.

## Features

- Support for over 100 programming languages.
- Easy lexer embedding for multi-language lexers.
- Universal color themes.
- Comparable speed to native Scintilla lexers.

## Enabling and Configuring the LPeg Lexer

Scintilla is not compiled with the LPeg lexer enabled by default (it is present, but empty). You need to manually enable it with the `LPEG_LEXER` flag when building Scintilla and its lexers. You also need to build and link the Lua source files contained in Scintilla's `lua/src/` directory to `lexers/LexLPeg.cxx`. If your application has its own copy of Lua, you can ignore Scintilla's copy and link to yours.

At this time, only the GTK, curses, and MinGW32 (for win32) platform makefiles facilitate enabling the LPeg lexer. For example, when building Scintilla, run `make LPEG_LEXER=1`. User contributions to facilitate this for the other platforms is encouraged.

When Scintilla is compiled with the LPeg lexer enabled, and after selecting it as the lexer to use via SCI_SETLEXER or SCI_SETLEXERLANGUAGE, the following property must be set via SCI_SETPROPERTY:

`lexer.lpeg.home` | The directory containing the Lua lexers. This is the path where you included Scintilla's `lexlua/` directory in your application's installation location.

The following properties are optional and may or may not be set:

`lexer.lpeg.color.theme` | The color theme to use. Color themes are located in the `lexlua/themes/` directory. Currently supported themes are `light`, `dark`, `scite`, and `curses`. Your application can define colors and styles manually through Scintilla properties. The theme files have examples.
`fold` | For Lua lexers that have a folder, folding is turned on if `fold` is set to `1`. The default is `0`.
`fold.by.indentation` | For Lua lexers that do not have a folder, if `fold.by.indentation` is set to `1`, folding is done based on indentation level (like Python). The default is `0`.
`fold.line.comments` | If `fold.line.comments` is set to `1`, multiple, consecutive line comments are folded, and only the top-level comment is shown. There is a small performance penalty for large source files when this option and folding are enabled. The default is `0`.
`fold.on.zero.sum.lines` | If `fold.on.zero.sum.lines` is set to `1`, lines that contain both an ending and starting fold point are marked as fold points. For example, the C line `} else {` would be marked as a fold point. The default is `0`.

## Using the LPeg Lexer

Your application communicates with the LPeg lexer using Scintilla's `SCI_PRIVATELEXERCALL` API. The operation constants recognized by the LPeg lexer are based on Scintilla's existing named constants. Note that some of the names of the operations do not make perfect sense. This is a tradeoff in order to reuse Scintilla's existing constants.

In the descriptions that follow, `SCI_PRIVATELEXERCALL(int operation, void *pointer)` means you would call Scintilla like `SendScintilla(sci, SCI_PRIVATELEXERCALL, operation, pointer);`

### Usage Example

The curses platform demo, jinx, has a C-source example for using the LPeg lexer. Additionally, here is a pseudo-code example:

        init_app() {
          sci = scintilla_new()
        }

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

        set_lexer(lang) {
          psci = SendScintilla(sci, SCI_GETDIRECTPOINTER, 0, 0)
          SendScintilla(sci, SCI_PRIVATELEXERCALL, SCI_SETDOCPOINTER, psci)
          SendScintilla(sci, SCI_PRIVATELEXERCALL, SCI_SETLEXERLANGUAGE, lang)
        }

`SCI_PRIVATELEXERCALL(SCI_CHANGELEXERSTATE, lua_State *L)
SCI_PRIVATELEXERCALL(SCI_GETDIRECTFUNCTION, int SciFnDirect)
SCI_PRIVATELEXERCALL(SCI_GETLEXERLANGUAGE, char *languageName) → int
SCI_PRIVATELEXERCALL(SCI_GETSTATUS, char *errorMessage) → int
SCI_PRIVATELEXERCALL(int styleNum, char *styleName) → int
SCI_PRIVATELEXERCALL(SCI_SETDOCPOINTER, int sci)
SCI_PRIVATELEXERCALL(SCI_SETLEXERLANGUAGE, languageName)
`

SCI_PRIVATELEXERCALL(SCI_CHANGELEXERSTATE, lua_State *L)
Tells the LPeg lexer to use `L` as its Lua state instead of creating a separate state.

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

The LPeg lexer will create a single `lexer` package (that can be used with Lua's `require` function), as well as a number of other variables in the `LUA_REGISTRYINDEX` table with the "sci_" prefix.

Rather than including the path to Scintilla's Lua lexers in the `package.path` of the given Lua state, set the "lexer.lpeg.home" property instead. The LPeg lexer uses that property to find and load lexers.

Usage:

        lua = luaL_newstate()
        SendScintilla(sci, SCI_PRIVATELEXERCALL, SCI_CHANGELEXERSTATE, lua)

SCI_PRIVATELEXERCALL(SCI_GETDIRECTFUNCTION, SciFnDirect)
Tells the LPeg lexer the address of `SciFnDirect`, the function that handles Scintilla messages.

Despite the name `SCI_GETDIRECTFUNCTION`, it only notifies the LPeg lexer what the value of `SciFnDirect` obtained from `SCI_GETDIRECTFUNCTION` is. It does not return anything. Use this if you would like to have the LPeg lexer set all Lua 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 document that was created using Scintilla's `SCI_CREATEDOCUMENT`. You must also use the `SCI_SETDOCPOINTER` LPeg lexer API call.

Usage:

        fn = SendScintilla(sci, SCI_GETDIRECTFUNCTION, 0, 0)
        SendScintilla(sci, SCI_PRIVATELEXERCALL, SCI_GETDIRECTFUNCTION, fn)

See also: `SCI_SETDOCPOINTER`

SCI_PRIVATELEXERCALL(SCI_GETLEXERLANGUAGE, char *languageName) → int
Returns the length of the string name of the current Lua 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`.

SCI_PRIVATELEXERCALL(SCI_GETSTATUS, char *errorMessage) → int
Returns the length of the error message of the LPeg lexer or Lua lexer error that occurred (if any), or stores the error message into the given buffer.

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

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

Usage:

        SendScintilla(sci, SCI_PRIVATELEXERCALL, SCI_GETSTATUS, errmsg)
        if (strlen(errmsg) > 0) { /* handle error */ }

SCI_PRIVATELEXERCALL(int styleNum, char *styleName) → int
Returns the length of the token name associated with the given style number or stores the style name into the given buffer. If the buffer is long enough, the string is terminated by a `0` character.

Usage:

        style = SendScintilla(sci, SCI_GETSTYLEAT, pos, 0)
        SendScintilla(sci, SCI_PRIVATELEXERCALL, style, token)
        // token now contains the name of the style at pos

SCI_PRIVATELEXERCALL(SCI_SETDOCPOINTER, int sci)
Tells the LPeg lexer the address of the Scintilla window (obtained via Scintilla's `SCI_GETDIRECTPOINTER`) 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` LPeg lexer API call. It must be made before each call to the `SCI_SETLEXERLANGUAGE` LPeg lexer API call.

Usage:

        SendScintilla(sci, SCI_PRIVATELEXERCALL, SCI_SETDOCPOINTER, sci)

See also: `SCI_GETDIRECTFUNCTION`, `SCI_SETLEXERLANGUAGE`

SCI_PRIVATELEXERCALL(SCI_SETLEXERLANGUAGE, const char *languageName)
Sets the current Lua lexer to `languageName`.

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

Usage:

        SendScintilla(sci, SCI_PRIVATELEXERCALL, SCI_SETLEXERLANGUAGE, "lua")

See also: `SCI_SETDOCPOINTER`

## Writing Lua Lexers

Lexers highlight the syntax of source code. Scintilla (the editing component behind Textadept) 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 Lua lexers with the aforementioned Textadept editor. Finally there are comments on lexer performance and limitations.

### Lexer Basics

The lexlua/ 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 100+ 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, Lua lexers for those languages are named "ansi_c", "dmd", and "rstats", respectively.

#### New Lexer Template

There is a lexlua/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. Consider this snippet from the template:

        -- ? LPeg lexer.

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

        local lex = lexer.new('?')

        -- Whitespace.
        local ws = token(lexer.WHITESPACE, lexer.space^1)
        lex:add_rule('whitespace', ws)

        [...]

        return lex

The first 3 lines of code simply define often used convenience variables. The fourth and last lines define and return the lexer object Scintilla uses; they are very important and must be part of every lexer. The fifth line defines something called a "token", an essential building block of lexers. You will learn about tokens shortly. The sixth line defines a lexer grammar rule, which you will learn about later, as well as token styles. (Be aware that it is common practice to combine these two lines for short rules.) Note, however, the `local` prefix in front of variables, which is needed so-as not to affect Lua's global environment. All in all, this is a minimal, working lexer that you can build on.

#### Tokens

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, keywords, built-in functions, constants, built-in libraries, identifiers, strings, comments, numbers, 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(lexer.WHITESPACE, lexer.space^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` 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.space`, `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 keywords, comments, and strings? Here are some examples.

Keywords

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(lexer.KEYWORD, lexer.word_match[[
          keyword_1 keyword_2 ... keyword_n
        ]])

        local case_insensitive_keyword = token(lexer.KEYWORD, lexer.word_match([[
          KEYWORD_1 keyword_2 ... KEYword_n
        ]], true))

        local hyphened_keyword = token(lexer.KEYWORD, lexer.word_match[[
          keyword-1 keyword-2 ... keyword-n
        ]])

In order to more easily separate or categorize keyword sets, you can use Lua line comments within keyword strings. Such comments will be ignored. For example:

        local keyword = token(lexer.KEYWORD, lexer.word_match[[
          -- Version 1 keywords.
          keyword_11, keyword_12 ... keyword_1n
          -- Version 2 keywords.
          keyword_21, keyword_22 ... keyword_2n
          ...
          -- Version N keywords.
          keyword_m1, keyword_m2 ... keyword_mn
        ]])

Comments

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

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

Strings

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

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

Numbers

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(lexer.NUMBER, lexer.float + lexer.integer)

However, some languages allow postfix characters on integers.

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

#### Rules

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 `lexer.add_rule()` call, which adds a rule to the lexer's grammar:

        lex:add_rule('whitespace', ws)

Each rule has an associated name, but 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 added to the grammar, the lexer tries to match the second rule added, and so on. Right now this lexer simply matches whitespace tokens under a rule named "whitespace".

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

        lex:add_rule('whitespace', token(lexer.WHITESPACE, ...))
        lex:add_rule('keyword', token(lexer.KEYWORD, ...))
        lex:add_rule('identifier', token(lexer.IDENTIFIER, ...))
        lex:add_rule('string', token(lexer.STRING, ...))
        lex:add_rule('comment', token(lexer.COMMENT, ...))
        lex:add_rule('number', token(lexer.NUMBER, ...))
        lex:add_rule('label', token(lexer.LABEL, ...))
        lex:add_rule('operator', token(lexer.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 added 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:

        lex:add_rule('whitespace', ws)
        ...
        lex:add_rule('error', token(lexer.ERROR, lexer.any))

This identifies and highlights any character not matched by an existing rule as a `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. That rule might look something like this:

        lex:add_rule('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, especially if they span multiple lines.

#### Summary

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 = lexer.STYLE_VARIABLE..',italics'

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

#### Token Styles

Lexers use the `lexer.add_style()` function to assign styles to particular tokens. Recall the token definition and from the lexer template:

        local ws = token(lexer.WHITESPACE, lexer.space^1)
        lex:add_rule('whitespace', ws)

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', lexer.space^1)

Assigning a style to this token looks like:

        lex:add_style('custom_whitespace', lexer.STYLE_WHITESPACE)

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

        local custom_style = lexer.STYLE_WHITESPACE..',back:$(color.grey)'
        lex:add_style('custom_whitespace', custom_style)

Notice that the lexer peforms Scintilla-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, create the lexer with an extra parameter:

        local lex = lexer.new('?', {lex_by_line = true})

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 into 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 = lexer.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
          end
        end)

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()` function:

        lex:embed(css, css_start_rule, css_end_rule)

##### 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, call `lexer.embed()` with switched arguments. For example, in the PHP lexer:

        local html = lexer.load('html')
        local php_start_rule = token('php_tag', '<?php ')
        local php_end_rule = token('php_tag', '?>')
        lex:add_style('php_tag', lexer.STYLE_EMBEDDED)
        html:embed(lex, 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 many Scintilla-based editors, such as Textadept, 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.add_fold_point()` function allows you to conveniently define fold points with such granularity. For example, consider C:

        lex:add_fold_point(lexer.OPERATOR, '{', '}')
        lex:add_fold_point(lexer.COMMENT, '/*', '*/')

The first assignment states that any '{' or '}' that the lexer recognized as an `lexer.OPERATOR` token is a 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 occurrences of these characters outside their defined tokens (such as in a string) as fold points. How do you specify fold keywords? Here is an example for Lua:

        lex:add_fold_point(lexer.KEYWORD, 'if', 'end')
        lex:add_fold_point(lexer.KEYWORD, 'do', 'end')
        lex:add_fold_point(lexer.KEYWORD, 'function', 'end')
        lex:add_fold_point(lexer.KEYWORD, 'repeat', 'until')

If your lexer has case-insensitive keywords as fold points, simply add a `case_insensitive_fold_points = true` option to `lexer.new()`, and specify keywords in lower case.

If your lexer needs to do some additional processing in order to determine if a token is a fold point, pass a function that returns an integer to `lex:add_fold_point()`. Returning `1` indicates the token is a beginning fold point and returning `-1` indicates the token is an ending fold point. Returning `0` indicates the token is not a fold point. For example:

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

        lex:add_fold_point('strange_token', '|', fold_strange_token)

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 fold point text starts at, and the fold point 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, create the lexer with a `fold_by_indentation = true` option:

        local lex = lexer.new('?', {fold_by_indentation = true})

### Using Lexers

#### Textadept

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.

### Migrating Legacy Lexers

Legacy lexers are of the form:

        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 = '?'}

        [... token and pattern definitions ...]

        M._rules = {
          {'rule', pattern},
          [...]
        }

        M._tokenstyles = {
          'token' = 'style',
          [...]
        }

        M._foldsymbols = {
          _patterns = {...},
          ['token'] = {['start'] = 1, ['end'] = -1},
          [...]
        }

        return M

While such legacy lexers will be handled just fine without any changes, it is recommended that you migrate yours. The migration process is fairly straightforward:

1. Replace all instances of `l` with `lexer`, as it's better practice and results in less confusion.
2. Replace `local M = {_NAME = '?'}` with `local lex = lexer.new('?')`, where `?` is the name of your legacy lexer. At the end of the lexer, change `return M` to `return lex`.
3. Instead of defining rules towards the end of your lexer, define your rules as you define your tokens and patterns using `lex:add_rule()`.
4. Similarly, any custom token names should have their styles immediately defined using `lex:add_style()`.
5. Convert any table arguments passed to `lexer.word_match()` to a space-separated string of words.
6. Replace any calls to `lexer.embed(M, child, ...)` and `lexer.embed(parent, M, ...)` with `lex:embed``(child, ...)` and `parent:embed(lex, ...)`, respectively.
7. Define fold points with simple calls to `lex:add_fold_point()`. No need to mess with Lua patterns anymore.
8. Any legacy lexer options such as `M._FOLDBYINDENTATION`, `M._LEXBYLINE`, `M._lexer`, etc. should be added as table options to `lexer.new()`.
9. Any external lexer rule fetching and/or modifications via `lexer._RULES` should be changed to use `lexer.get_rule()` and `lexer.modify_rule()`.

As an example, consider the following sample legacy 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 = 'legacy'}

        local ws = token(l.WHITESPACE, l.space^1)
        local comment = token(l.COMMENT, '#' * l.nonnewline^0)
        local string = token(l.STRING, l.delimited_range('"'))
        local number = token(l.NUMBER, l.float + l.integer)
        local keyword = token(l.KEYWORD, word_match{'foo', 'bar', 'baz'})
        local custom = token('custom', P('quux'))
        local identifier = token(l.IDENTIFIER, l.word)
        local operator = token(l.OPERATOR, S('+-*/%^=<>,.()[]{}'))

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

        M._tokenstyles = {
          'custom' = l.STYLE_KEYWORD..',bold'
        }

        M._foldsymbols = {
          _patterns = {'[{}]'},
          [l.OPERATOR] = {['{'] = 1, ['}'] = -1}
        }

        return M

Following the migration steps would yield:

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

        local lex = lexer.new('legacy')

        lex:add_rule('whitespace', token(lexer.WHITESPACE, lexer.space^1))
        lex:add_rule('keyword', token(lexer.KEYWORD, word_match[[foo bar baz]]))
        lex:add_rule('custom', token('custom', P('quux')))
        lex:add_style('custom', lexer.STYLE_KEYWORD..',bold')
        lex:add_rule('identifier', token(lexer.IDENTIFIER, lexer.word))
        lex:add_rule('string', token(lexer.STRING, lexer.delimited_range('"')))
        lex:add_rule('comment', token(lexer.COMMENT, '#' * lexer.nonnewline^0))
        lex:add_rule('number', token(lexer.NUMBER, lexer.float + lexer.integer))
        lex:add_rule('operator', token(lexer.OPERATOR, S('+-*/%^=<>,.()[]{}')))

        lex:add_fold_point(lexer.OPERATOR, '{', '}')

        return lex

### Considerations

#### Performance

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 Lua lexers and Scintilla's C++ ones. Optimize lexers for speed by re-arranging `lexer.add_rule()` calls so that the most common rules match first. Do keep in mind that order matters for similar rules.

In some cases, folding may be far more expensive than lexing, particularly in lexers with a lot of potential fold points. If your lexer is exhibiting signs of slowness, try disabling folding your text editor first. If that speeds things up, you can try reducing the number of fold points you added, overriding `lexer.fold()` with your own implementation, or simply eliminating folding support from your lexer.

#### Limitations

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; ?>">

will not style correctly.

#### Troubleshooting

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.

#### Risks

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.

#### Acknowledgements

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

## Lua `lexer` module API fields

### `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.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.

### `lexer.STYLE_FOLDDISPLAYTEXT` (string)

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.

### `lexer.STYLE_PREPROCESSOR` (string)

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.FOLD_BASE` The initial fold level.
- `lexer.FOLD_BLANK` The line is blank.
- `lexer.FOLD_HEADER` The line is a header, or fold point.

### `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.path` (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.print` (pattern)

A pattern that matches any printable character (' ' to '~').

### `lexer.property` (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 '~').

### `lexer.space` (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').

## Lua `lexer` module API functions

### `lexer.add_fold_point` (lexer, token_name, start_symbol, end_symbol)

Adds to lexer lexer a fold point whose beginning and end tokens are string token_name tokens with string content start_symbol and end_symbol, respectively. In the event that start_symbol may or may not be a fold point depending on context, and that additional processing is required, end_symbol may be a function that ultimately returns `1` (indicating a beginning fold point), `-1` (indicating an ending fold point), or `0` (indicating no fold point). That function is passed the following arguments:

- `text`: The text being processed for fold points.
- `pos`: The position in text of the beginning of the line currently being processed.
- `line`: The text of the line currently being processed.
- `s`: The position of start_symbol in line.
- `symbol`: start_symbol itself.

Fields:

- `lexer`: The lexer to add a fold point to.
- `token_name`: The token name of text that indicates a fold point.
- `start_symbol`: The text that indicates the beginning of a fold point.
- `end_symbol`: Either the text that indicates the end of a fold point, or a function that returns whether or not start_symbol is a beginning fold point (1), an ending fold point (-1), or not a fold point at all (0).

Usage:

- `lex:add_fold_point(lexer.OPERATOR, '{', '}')`
- `lex:add_fold_point(lexer.KEYWORD, 'if', 'end')`
- `lex:add_fold_point(lexer.COMMENT, '#', lexer.fold_line_comments('#'))`
- `lex:add_fold_point('custom', function(text, pos, line, s, symbol) ... end)`

### `lexer.add_rule` (lexer, id, rule)

Adds pattern rule identified by string id to the ordered list of rules for lexer lexer.

Fields:

- `lexer`: The lexer to add the given rule to.
- `id`: The id associated with this rule. It does not have to be the same as the name passed to `token()`.
- `rule`: The LPeg pattern of the rule.

See also:

- `lexer.modify_rule`

### `lexer.add_style` (lexer, token_name, style)

Associates string token_name in lexer lexer with Scintilla style string style. Style strings are comma-separated property settings. Available property settings are:

- `font:name`: Font name.
- `size:int`: Font size.
- `bold` or `notbold`: Whether or not the font face is bold.
- `weight:int`: Font weight (between 1 and 999).
- `italics` or `notitalics`: Whether or not the font face is italic.
- `underlined` or `notunderlined`: Whether or not the font face is underlined.
- `fore:color`: Font face foreground color in "#RRGGBB" or 0xBBGGRR format.
- `back:color`: Font face background color in "#RRGGBB" or 0xBBGGRR format.
- `eolfilled` or `noteolfilled`: Whether or not the background color extends to the end of the line.
- `case:char`: Font case ('u' for uppercase, 'l' for lowercase, and 'm' for mixed case).
- `visible` or `notvisible`: Whether or not the text is visible.
- `changeable` or `notchangeable`: Whether or not the text is changeable or read-only.

Property settings may also contain "$(property.name)" expansions for properties defined in Scintilla, theme files, etc.

Fields:

- `lexer`: The lexer to add a style to.
- `token_name`: The name of the token to associated with the style.
- `style`: A style string for Scintilla.

Usage:

- `lex:add_style('longstring', lexer.STYLE_STRING)`
- `lex:add_style('deprecated_function', lexer.STYLE_FUNCTION..',italics')`
- `lex:add_style('visible_ws', lexer.STYLE_WHITESPACE..',back:$(color.grey)')`

### `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.

Fields:

- `chars`: The character(s) that bound the matched range.
- `single_line`: Optional flag indicating whether or not the range must be on a single line.
- `no_escape`: Optional flag indicating whether or not the range end character may be escaped by a '\' character.
- `balanced`: Optional flag indicating whether or not to match a balanced range, like the "%b" Lua pattern. This flag only applies if chars consists of two different characters (e.g. "()").

Usage:

- `local dq_str_escapes = lexer.delimited_range('"')`
- `local dq_str_noescapes = lexer.delimited_range('"', false, true)`
- `local unbalanced_parens = lexer.delimited_range('()')`
- `local balanced_parens = lexer.delimited_range('()', false, false, true)`

Return:

- pattern

See also:

- `lexer.nested_pair`

### `lexer.embed` (lexer, child, start_rule, end_rule)

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

Fields:

- `lexer`: The parent lexer.
- `child`: The child lexer.
- `start_rule`: The pattern that signals the beginning of the embedded lexer.
- `end_rule`: The pattern that signals the end of the embedded lexer.

Usage:

- `html:embed(css, css_start_rule, css_end_rule)`
- `html:embed(lex, php_start_rule, php_end_rule) -- from php lexer`

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

Determines fold points in a chunk of text text using lexer lexer, returning a table of fold levels associated with line numbers. text starts at position start_pos on line number start_line with a beginning fold level of start_level in the buffer.

Fields:

- `lexer`: The lexer to fold text with.
- `text`: The text in the buffer to fold.
- `start_pos`: The position in the buffer text starts at, starting at zero.
- `start_line`: The line number text starts on.
- `start_level`: The fold level text starts on.

Return:

- table of fold levels associated with line numbers.

### `lexer.fold_line_comments` (prefix)

Returns a fold function (to be passed to `lexer.add_fold_point()`) that folds consecutive line comments that start with string prefix.

Fields:

- `prefix`: The prefix string defining a line comment.

Usage:

- `lex:add_fold_point(lexer.COMMENT, '--', lexer.fold_line_comments('--'))`
- `lex:add_fold_point(lexer.COMMENT, '//', lexer.fold_line_comments('//'))`

### `lexer.get_rule` (lexer, id)

Returns the rule identified by string id.

Fields:

- `lexer`: The lexer to fetch a rule from.
- `id`: The id of the rule to fetch.

Return:

- pattern

### `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.

Fields:

- `s`: String character set like one passed to `lpeg.S()`.

Usage:

- `local regex = lexer.last_char_includes('+-*!%^&|=,([{') * lexer.delimited_range('/')`

Return:

- pattern

### `lexer.lex` (lexer, text, init_style)

Lexes a chunk of text text (that has an initial style number of init_style) using lexer lexer, returning a table of token names and positions.

Fields:

- `lexer`: The lexer to lex text with.
- `text`: The text in the buffer to lex.
- `init_style`: The current style. Multiple-language lexers use this to determine which language to start lexing in.

Return:

- table of token names and positions.

### `lexer.line_from_position` (pos)

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

Fields:

- `pos`: The position to get the line number of.

Return:

- number

### `lexer.load` (name, alt_name, cache)

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 this module as a Lua library.

Fields:

- `name`: The name of the lexing language.
- `alt_name`: The alternate name of the lexing language. This is useful for embedding the same child lexer with multiple sets of start and end tokens.
- `cache`: Flag indicating whether or not to load lexers from the cache. This should only be `true` when initially loading a lexer (e.g. not from within another lexer for embedding purposes). The default value is `false`.

Return:

- lexer object

### `lexer.modify_rule` (lexer, id, rule)

Replaces in lexer lexer the existing rule identified by string id with pattern rule.

Fields:

- `lexer`: The lexer to modify.
- `id`: The id associated with this rule.
- `rule`: The LPeg pattern of the rule.

### `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)`.

Fields:

- `start_chars`: The string starting a nested sequence.
- `end_chars`: The string ending a nested sequence.

Usage:

- `local nested_comment = lexer.nested_pair('/*', '*/')`

Return:

- pattern

See also:

- `lexer.delimited_range`

### `lexer.new` (name, opts)

Creates a returns a new lexer with the given name.

Fields:

- `name`: The lexer's name.
- `opts`: Table of lexer options. Options currently supported:
  - `lex_by_line`: Whether or not the lexer only processes whole lines of text (instead of arbitrary chunks of text) at a time. Line lexers cannot look ahead to subsequent lines. The default value is `false`.
  - `fold_by_indentation`: Whether or not the lexer does not define any fold points and that fold points should be calculated based on changes in line indentation. The default value is `false`.
  - `case_insensitive_fold_points`: Whether or not fold points added via `lexer.add_fold_point()` ignore case. The default value is `false`.
  - `inherit`: Lexer to inherit from. The default value is `nil`.

Usage:

- `lexer.new('rhtml', {inherit = lexer.load('html')})`

### `lexer.starts_line` (patt)

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

Fields:

- `patt`: The LPeg pattern to match on the beginning of a line.

Usage:

- `local preproc = token(lexer.PREPROCESSOR, lexer.starts_line('#') * lexer.nonnewline^0)`

Return:

- pattern

### `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 via `lexer.add_style()`.

Fields:

- `name`: The name of token. If this name is not a predefined token name, then a style needs to be assiciated with it via `lexer.add_style()`.
- `patt`: The LPeg pattern associated with the token.

Usage:

- `local ws = token(lexer.WHITESPACE, lexer.space^1)`
- `local annotation = token('annotation', '@' * lexer.word)`

Return:

- pattern

### `lexer.word_match` (words, case_insensitive, word_chars)

Creates and returns a pattern that matches any single word in string words. 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. If words is a multi-line string, it may contain Lua line comments (`--`) that will ultimately be ignored.

Fields:

- `words`: A string list of words separated by spaces.
- `case_insensitive`: Optional boolean flag indicating whether or not the word match is case-insensitive. The default value is `false`.
- `word_chars`: Unused legacy parameter.

Usage:

- `local keyword = token(lexer.KEYWORD, word_match[[foo bar baz]])`
- `local keyword = token(lexer.KEYWORD, word_match([[foo-bar foo-baz bar-foo bar-baz baz-foo baz-bar]], true))`

Return:

- pattern

## Supported Languages

Scintilla has Lua lexers for all of the languages below. Languages denoted by a `*` have native folders. For languages without native folding support, folding based on indentation can be used if `fold.by.indentation` is enabled.

1. Actionscript`*`
2. Ada
3. ANTLR`*`
4. APDL`*`
5. APL
6. Applescript
7. ASM`*` (NASM)
8. ASP`*`
9. AutoIt
10. AWK`*`
11. Batch`*`
12. BibTeX`*`
13. Boo
14. C`*`
15. C++`*`
16. C#`*`
17. ChucK
18. CMake`*`
19. Coffeescript
20. ConTeXt`*`
21. CSS`*`
22. CUDA`*`
23. D`*`
24. Dart`*`
25. Desktop Entry
26. Diff
27. Django`*`
28. Dockerfile
29. Dot`*`
30. Eiffel`*`
31. Elixir
32. Erlang`*`
33. F#
34. Faust
35. Fish`*`
36. Forth
37. Fortran
38. GAP`*`
39. gettext
40. Gherkin
41. GLSL`*`
42. Gnuplot
43. Go`*`
44. Groovy`*`
45. Gtkrc`*`
46. Haskell
47. HTML`*`
48. Icon`*`
49. IDL
50. Inform
51. ini
52. Io`*`
53. Java`*`
54. Javascript`*`
55. JSON`*`
56. JSP`*`
57. LaTeX`*`
58. Ledger
59. LESS`*`
60. LilyPond
61. Lisp`*`
62. Literate Coffeescript
63. Logtalk
64. Lua`*`
65. Makefile
66. Man Page
67. Markdown
68. MATLAB`*`
69. MoonScript
70. Myrddin
71. Nemerle`*`
72. Nim
73. NSIS
74. Objective-C`*`
75. OCaml
76. Pascal
77. Perl`*`
78. PHP`*`
79. PICO-8`*`
80. Pike`*`
81. PKGBUILD`*`
82. Postscript
83. PowerShell`*`
84. Prolog
85. Properties
86. Pure
87. Python
88. R
89. rc`*`
90. REBOL`*`
91. Rexx`*`
92. ReStructuredText`*`
93. RHTML`*`
94. Ruby`*`
95. Ruby on Rails`*`
96. Rust`*`
97. Sass`*`
98. Scala`*`
99. Scheme`*`
100. Shell`*`
101. Smalltalk`*`
102. Standard ML
103. SNOBOL4
104. SQL
105. TaskPaper
106. Tcl`*`
107. TeX`*`
108. Texinfo`*`
109. TOML
110. Vala`*`
111. VBScript
112. vCard`*`
113. Verilog`*`
114. VHDL
115. Visual Basic
116. Windows Script File`*`
117. XML`*`
118. Xtend`*`
119. YAML

## Code Contributors

- Alejandro Baez
- Alex Saraci
- Brian Schott
- Carl Sturtivant
- Chris Emerson
- Christian Hesse
- David B. Lamkins
- Heck Fy
- Jason Schindler
- Jeff Stone
- Joseph Eib
- Joshua Krämer
- Klaus Borges
- Larry Hynes
- M Rawash
- Marc André Tanner
- Markus F.X.J. Oberhumer
- Martin Morawetz
- Michael Forney
- Michael T. Richter
- Michel Martens
- Murray Calavera
- Neil Hodgson
- Olivier Guibé
- Peter Odding
- Piotr Orzechowski
- Richard Philips
- Robert Gieseke
- Roberto Ierusalimschy
- S. Gilles
- Stéphane Rivière
- Tymur Gubayev
- Wolfgang Seeberg