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Language Service

The library includes a built-in language service that provides IDE-like features for expr-eval expressions. This is useful for integrating expr-eval into code editors like Monaco Editor (used by VS Code).

Features

  • Code Completions - Autocomplete for functions, operators, keywords, and user-defined variables
  • Hover Information - Documentation tooltips when hovering over functions and variables
  • Syntax Highlighting - Token-based highlighting for numbers, strings, keywords, operators, etc.

Basic Usage

import { createLanguageService } from '@pro-fa/expr-eval';

const ls = createLanguageService();

// Define variables available in your expressions
const variables = { x: 42, user: { name: 'Ada' }, flag: true };

// Get completions at a position
const completions = ls.getCompletions({
    textDocument: doc,  // LSP-compatible text document
    position: { line: 0, character: 5 },
    variables
});

// Get hover information
const hover = ls.getHover({
    textDocument: doc,
    position: { line: 0, character: 3 },
    variables
});

// Get syntax highlighting tokens
const tokens = ls.getHighlighting(doc);

Monaco Editor Integration Sample

A complete working example of Monaco Editor integration is included in the repository. To run it:

# Build the UMD bundle and start the sample server
npm run monaco-sample:serve

Then open http://localhost:8080 in your browser. The sample demonstrates:

  • Autocompletion for built-in functions (sum, max, min, etc.) and user variables
  • Hover documentation for functions and variables
  • Live syntax highlighting
  • Real-time expression evaluation

The sample code is located in samples/language-service-sample/ and shows how to:

  1. Register a custom language with Monaco
  2. Connect the language service to Monaco's completion and hover providers
  3. Apply syntax highlighting using decorations
  4. Create an LSP-compatible text document wrapper for Monaco models