Syntax Highlighting¶

Token-based syntax highlighting is configured in a colorer section of an ESV file. Such a section can contain style definitions and styling rules.

Style Definitions¶

Style definitions bind an identifier to a style for later reuse, using the syntax:

  $ID = $Style

Styles¶

A style specifies a combination of a foreground color, optional background color, and optional font style. Colors are specified as Red-Green-Blue values ranging from 0 (none) to 255 (full). The possible font attributes are:

Font attribute	Description
(none)	Normal font.
`bold`	Bold font.
`italic`	Italic font.
`bold italic`	Bond and italic font.
`italic bold`	Same as `bold italic`.

For example, the following style definitions bind the red, green, and blue colors:

colorer

  red   = 255 0 0
  green = 0 255 0
  blue  = 0 0 255

An optional background color can be set by adding another RGB value:

colorer

  redWithGreenBackground = 255 0 0 0 255 0

The font attributes can be used to make the font bold or italic:

colorer

  redWithBold   = 255 0 0 bold
  redWithItalic = 255 0 0 italic
  redWithGreenBackgroundWithBoldItalic = 255 0 0 0 255 0 bold italic

Style Rules¶

Style rules assign a style to matched tokens with syntax:

$Matcher : $Style

Or assigns a previously defined style definition:

$Matcher : $Ref

The left hand side of style rules matches a token, whereas the right hand side assigns a style by referring to a previously defined style definition, or by directly assigning a style. For example, the following matches a token type and references a style definition:

colorer

  operator : black

whereas the following matches a token with a sort and constructor, and directly assigns a style:

colorer

  ClassBodyDec.MethodDec : 0 255 0

Matchers¶

There are several ways in which the matcher on the left-hand side of a style rule can be specified: by type, by sort, by constructor, or by sort and constructor.

Match by Sort and Constructor¶

The combination of a token sort and constructor can be matched by specifying the $Sort.$Constructor. For example:

colorer

  ClassBodyDec.MethodDec : yellow
  ClassBodyDec.FieldDec  : red

Match by Constructor¶

It is also possible to match constructors, regardless of their token sorts, using _ in place of the sort name. For example:

colorer

  _.Str     : blue
  _.StrCong : blue
  _.QStr    : blue
  _.QDollar : blue
  _.QBr     : gray

Match by Sort¶

Additionally, it is possible to match any constructor for a specific sort. For this, just specify the name of the sort, $Sort. For example:

colorer

  ID       : darkblue
  TYPEID   : blue
  JQTYPEID : blue
  PQTYPEID : blue
  FUNCID   : 153 51 0
  JFUNCID  : 153 51 0
  STRING   : 177 47 2

Match by Type¶

Finally, the following built-in token types can be matched on:

identifier — matches identifiers, found by lexical non-terminals without numbers;
keyword — matches keywords, found by terminals in the syntax definition;
layout — matches layout, such as whitespace and comments, found by layout definition;
number — matches numbers, found by lexical non-terminals with numbers;
operator — matches operations, found by terminals that contain just symbols (no characters);
string — matches strings, found by lexical non-terminals that include quotation marks;
unknown — matches tokens which the parser was unable to infer a type for.
var
error

For example, the following code defines a simple highlighting with token types:

colorer

  keyword    : 153 51 153
  identifier : black
  string     : 177 47 2
  number     : 17 131 22
  operator   : black
  layout     : 63 127 95 italic

Last update: October 17, 2024
Created: October 17, 2024