Write a TextMate Grammar from Scratch | Web Formatter Blog

Introduction to TextMate Grammars

Syntax highlighting is a fundamental feature of modern code editors that makes code more readable and helps developers identify different elements at a glance. Behind the scenes, most editors use TextMate grammars to define how different parts of code should be colored and styled.

In this comprehensive guide, we'll explore how to create a TextMate grammar from scratch, enabling you to build custom syntax highlighting for any language or file format. Whether you're developing a new programming language, working with a domain-specific language, or simply want to improve highlighting for an existing format, this guide will walk you through the entire process.

What is a TextMate Grammar?

A TextMate grammar is a structured definition that tells a code editor how to parse and colorize text. Originally developed for the TextMate editor on macOS, these grammars have become the de facto standard for syntax highlighting across many popular editors, including Visual Studio Code, Atom, Sublime Text, and GitHub's web interface.

TextMate grammars use a combination of JSON (or XML/PLIST) and regular expressions to:

• Identify different elements in code (keywords, strings, comments, etc.)
• Assign "scope names" to these elements
• Allow the editor's theme to apply appropriate styling based on these scopes

The beauty of TextMate grammars is their portability—once created, they can often be used across multiple editors with minimal modifications.

Why Create a Custom Grammar?

There are several compelling reasons to create a custom TextMate grammar:

• New languages: If you're developing a new programming language or DSL, a custom grammar provides proper syntax highlighting
• Improved highlighting: Existing grammars for some languages may be incomplete or outdated
• Custom file formats: For proprietary or specialized file formats that lack syntax highlighting
• Learning: Understanding grammars helps you better comprehend how editors work
• Specialized needs: Highlighting specific patterns unique to your workflow or domain

TextMate Grammar Structure

Before diving into creation, let's understand the structure of a TextMate grammar. At its core, a grammar is a JSON (or PLIST) file with specific properties that define how text should be parsed.

Here's a simplified example of a TextMate grammar structure:

{
  "name": "Example Language",
  "scopeName": "source.example",
  "fileTypes": ["ex", "exm"],
  "patterns": [
    {
      "match": "\\b(if|else|while|for)\\b",
      "name": "keyword.control.example"
    },
    {
      "match": "#.*$",
      "name": "comment.line.number-sign.example"
    },
    {
      "begin": "\\"",
      "end": "\\"",
      "name": "string.quoted.double.example"
    }
  ],
  "repository": {
    "strings": {
      "patterns": [
        {
          "match": "\\\\.",
          "name": "constant.character.escape.example"
        }
      ]
    }
  }
}

Understanding Scope Names

Scope names are hierarchical identifiers that describe the purpose of a piece of text. They follow a dot-notation convention and are used by themes to apply consistent styling across different languages.

Common scope name categories include:

Conclusion

Creating a TextMate grammar for syntax highlighting is a powerful way to enhance the coding experience for a specific language or format. By following the steps and techniques outlined in this guide, you can create professional-quality highlighting that improves code readability and helps developers work more efficiently.

Remember to start simple, test thoroughly, and build up your grammar incrementally. With practice, you'll be able to create sophisticated highlighting for even the most complex languages and formats.