Scintillua API Documentation

Overview

The Scintillua Scintilla lexer has its own API in order 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() {
  SetLibraryProperty("lpeg.home", "/home/mitchell/app/lexers")
  SetLibraryProperty("lpeg.color.theme", "light")
  sci = scintilla_new()
}

create_doc() {
  doc = SendScintilla(sci, SCI_CREATEDOCUMENT)
  SendScintilla(sci, SCI_SETDOCPOINTER, 0, doc)
  SendScintilla(sci, SCI_SETILEXER, 0, CreateLexer(NULL))
  fn = SendScintilla(sci, SCI_GETDIRECTFUNCTION)
  SendScintilla(sci, SCI_PRIVATELEXERCALL, SCI_GETDIRECTFUNCTION, fn)
  psci = SendScintilla(sci, SCI_GETDIRECTPOINTER)
  SendScintilla(sci, SCI_PRIVATELEXERCALL, SCI_SETDOCPOINTER, psci)
  SendScintilla(sci, SCI_PRIVATELEXERCALL, SCI_SETLEXERLANGUAGE, "lua")
}

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

Functions defined by Scintillua

SCI_PRIVATELEXERCALL(SCI_CHANGELEXERSTATE, lua)

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

lua must have already opened the “base”, “string”, “table”, and “lpeg” libraries.

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.

Fields:

Usage:

SCI_PRIVATELEXERCALL(SCI_GETDIRECTFUNCTION, SciFnDirect)

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.

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Usage:

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SCI_PRIVATELEXERCALL(SCI_GETLEXERLANGUAGE, languageName)

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.

Fields:

SCI_PRIVATELEXERCALL(SCI_GETNAMEDSTYLES, styleName)

Returns the style number associated with styleName, or STYLE_DEFAULT if styleName is not known.

Fields:

Usage:

SCI_PRIVATELEXERCALL(SCI_GETSTATUS)

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.

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Usage:

SCI_PRIVATELEXERCALL(SCI_LOADLEXERLIBRARY, path)

Tells Scintillua that the given path is where Scintillua’s lexers are located, or is a path that contains additional lexers and/or themes to load (e.g. user-defined lexers/themes).

This call may be made multiple times in order to support lexers and themes across multiple directories.

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Usage:

SCI_PRIVATELEXERCALL(SCI_PROPERTYNAMES, names)

Returns the length of a ‘\n’-separated list of known lexer names, or stores the lexer list into the given buffer. If the buffer is long enough, the string is terminated by a 0 character.

The lexers in this list can be passed to the SCI_SETLEXERLANGUAGE Scintillua API call.

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SCI_PRIVATELEXERCALL(SCI_SETDOCPOINTER, sci)

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.

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SCI_PRIVATELEXERCALL(SCI_SETLEXERLANGUAGE, languageName)

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.

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Usage:

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SCI_PRIVATELEXERCALL(styleNum, style)

Returns the length of the associated SciTE-formatted style definition for the given style number or stores that string into the given buffer. If the buffer is long enough, the string is terminated by a 0 character.

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.

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The lexer Lua Module


Lexes Scintilla documents and source code with Lua and LPeg.

Writing Lua Lexers

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 number of 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 also 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 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 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, 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. Consider this snippet from the template:

-- ? LPeg lexer.

local lexer = require('lexer')
local token, word_match = lexer.token, lexer.word_match
local P, S = lpeg.P, 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.alpha, lexer.digit, lexer.alnum, lexer.lower, lexer.upper, lexer.xdigit, lexer.graph, lexer.print, lexer.punct, lexer.space, lexer.newline, lexer.nonnewline, lexer.dec_num, lexer.hex_num, lexer.oct_num, lexer.integer, lexer.float, lexer.number, 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.to_eol('#'))
local c_line_comment = token(lexer.COMMENT, lexer.to_eol('//', true))

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.range('/*', '*/'))

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

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. lexer.range() handles escapes inherently.

local dq_str = lexer.range('"')
local sq_str = lexer.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 predefined LPeg pattern:

local number = token(lexer.NUMBER, lexer.number)

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 Lua tables of properties. 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 are contained in lexer.styles, and you may define your own styles. See that table’s documentation for more information. 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.styles.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 table:

local style_nothing = {}

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

local style_bold = {bold = true}

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

local style_static_var = lexer.styles.variable .. {italics = true}

The color theme files in the lexers/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.styles.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:

lex:add_style('custom_whitespace',
              lexer.styles.whitespace .. {back = lexer.colors.grey})

Remember to refrain from assigning specific colors in styles, but in this case, all user color themes probably define colors.grey.

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.styles.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 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.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.

SciTE

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

file.patterns.[lexer_name]=[file_patterns]
lexer.$(file.patterns.[lexer_name])=[lexer_name]

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.

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 Scintillua will handle such legacy lexers 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, S = lpeg.P, 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.styles.keyword .. {bold = true})
lex:add_rule('identifier', token(lexer.IDENTIFIER, lexer.word))
lex:add_rule('string', token(lexer.STRING, lexer.range('"')))
lex:add_rule('comment', token(lexer.COMMENT, lexer.to_eol('#')))
lex:add_rule('number', token(lexer.NUMBER, lexer.number))
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 in 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 provided inspiration, 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.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.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_by_indentation (boolean)

Whether or not to fold based on indentation level if a lexer does not have a folder. Some lexers automatically enable this option. It is disabled by default. This is an alias for lexer.property['fold.by.indentation'] = '1|0'.

lexer.fold_compact (boolean)

Whether or not blank lines after an ending fold point are included in that fold. This option is disabled by default. This is an alias for lexer.property['fold.compact'] = '1|0'.

lexer.fold_level (table, Read-only)

Table of fold level bit-masks for line numbers starting from 1. Fold level masks are composed of an integer level combined with any of the following bits:

lexer.fold_line_groups (boolean)

Whether or not to fold multiple, consecutive line groups (such as line comments and import statements) and only show the top line. This option is disabled by default. This is an alias for lexer.property['fold.line.groups'] = '1|0'.

lexer.fold_on_zero_sum_lines (boolean)

Whether or not to mark as a fold point lines that contain both an ending and starting fold point. For example, } else { would be marked as a fold point. This option is disabled by default. This is an alias for lexer.property['fold.on.zero.sum.lines'] = '1|0'.

lexer.folding (boolean)

Whether or not folding is enabled for the lexers that support it. This option is disabled by default. This is an alias for lexer.property['fold'] = '1|0'.

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 1.

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 1. 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 a sequence of end of line characters.

lexer.nonnewline (pattern)

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

lexer.number (pattern)

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

lexer.oct_num (pattern)

A pattern that matches an octal number.

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’).

Functions defined by lexer

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:

Fields:

Usage:

lexer.add_rule(lexer, id, rule)

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

Fields:

See also:

lexer.add_style(lexer, token_name, style)

Associates string token_name in lexer lexer with style table style. style may have the following fields:

Field values may also contain “$(property.name)” expansions for properties defined in Scintilla, theme files, etc.

Fields:

Usage:

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:

Usage:

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:

Return:

lexer.fold_consecutive_lines(prefix)

Returns for lexer.add_fold_point() the parameters needed to fold consecutive lines that start with string prefix.

Fields:

Usage:

lexer.get_rule(lexer, id)

Returns the rule identified by string id.

Fields:

Return:

lexer.last_char_includes(s)

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

Fields:

Usage:

Return:

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:

Return:

lexer.line_from_position(pos)

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

Fields:

Return:

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 Scintillua as a Lua library.

Fields:

Return:

lexer.modify_rule(lexer, id, rule)

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

Fields:

lexer.new(name, opts)

Creates a returns a new lexer with the given name.

Fields:

Usage:

lexer.range(s, e, single_line, escapes, balanced)

Creates and returns a pattern that matches a range of text bounded by strings or patterns s and e. This is a convenience function for matching more complicated ranges like strings with escape characters, balanced parentheses, and block comments (nested or not). e is optional and defaults to s. single_line indicates whether or not the range must be on a single line; escapes indicates whether or not to allow ‘' as an escape character; and balanced indicates whether or not to handle balanced ranges like parentheses, and requires s and e to be different.

Fields:

Usage:

Return:

lexer.starts_line(patt)

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

Fields:

Usage:

Return:

lexer.to_eol(prefix, escape)

Creates and returns a pattern that matches from string or pattern prefix until the end of the line. escape indicates whether the end of the line can be escaped with a ‘' character.

Fields:

Usage:

Return:

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:

Usage:

Return:

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:

Usage:

Return:

Tables defined by lexer

lexer.colors

Map of color name strings to color values in 0xBBGGRR or "#RRGGBB" format. Note: for applications running within a terminal emulator, only 16 color values are recognized, regardless of how many colors a user’s terminal actually supports. (A terminal emulator’s settings determines how to actually display these recognized color values, which may end up being mapped to a completely different color set.) In order to use the light variant of a color, some terminals require a style’s bold attribute must be set along with that normal color. Recognized color values are black (0x000000), red (0x000080), green (0x008000), yellow (0x008080), blue (0x800000), magenta (0x800080), cyan (0x808000), white (0xC0C0C0), light black (0x404040), light red (0x0000FF), light green (0x00FF00), light yellow (0x00FFFF), light blue (0xFF0000), light magenta (0xFF00FF), light cyan (0xFFFF00), and light white (0xFFFFFF).

lexer.styles

Map of style names to style definition tables.

Style names consist of the following default names as well as the token names defined by lexers.

Style definition tables may contain the following fields: