Quick Start

Highlighting takes three steps: load a grammar, pick how you want the output, and pass it some code.

A first grammar

A TextMate grammar is JSON describing the patterns of a language. A tiny one is enough to start — keywords, numbers, strings, and line comments:

import io.github.edadma.highlighter.*

val grammar = """{
  "scopeName": "source.example",
  "patterns": [
    { "match": "\\b(val|def|if|else)\\b", "name": "keyword.control" },
    { "match": "\\b\\d+\\b", "name": "constant.numeric" },
    { "begin": "\"", "end": "\"", "name": "string.quoted.double" },
    { "match": "//.*$", "name": "comment.line" }
  ]
}"""

Build a highlighter

Highlighter.fromJson parses the grammar and returns Either[String, Highlighter] — a Left carries a parse error message, so this never throws on a bad grammar:

val Right(hl) = Highlighter.fromJson(grammar, ClassMode("hl-")): @unchecked

Highlight some code

println(hl.highlight("val x = 42"))
// <span class="hl-keyword">val</span> x = <span class="hl-number">42</span>

That is the whole loop. From here:

• Loading Grammars — use a real VS Code .tmLanguage.json, and the grammar features highlighter supports.
• HTML Rendering — CSS-class output versus inline theme colours.
• Themes — the built-in colour schemes and writing your own.
• Tokens — skip the HTML and render the tokens yourself.