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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


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:


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

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


  redWithGreenBackground = 255 0 0 0 255 0

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


  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:


  operator : black

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


  ClassBodyDec.MethodDec : 0 255 0


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:


  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:


  _.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:


  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:


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

Last update: April 19, 2024
Created: April 19, 2024