FEEL Expression Language

Complete FEEL (Friendly Enough Expression Language) support for Visual Studio Code with advanced syntax highlighting and intelligent auto-formatting.

Features

🎨 Syntax Highlighting

• Rich color coding for FEEL keywords, operators, and functions
• Smart property highlighting with improved visibility
• Context-aware highlighting for different identifier types
• Built-in function recognition with proper scoping
• String and numeric literal highlighting

🔧 Auto-Formatting

• Smart indentation for nested expressions and control structures
• Configurable formatting rules
• Preserve user intent while maintaining consistent style
• Format on save support

⚡ Developer Experience

• Go to Definition - Ctrl+Click (Windows/Linux) or Cmd+Click (macOS) to navigate to property definitions
• Find All References - Find all usages of a property across the file
• Auto-closing brackets and quotes ({}, [], (), "")
• Smart bracket matching with visual indicators
• Comment toggling support (// and /* */)
• Code folding for better navigation
• Word-based navigation optimized for FEEL identifiers

🔍 FEEL Previewer

• Real-time Expression Evaluation - Test FEEL expressions with live context data
• JSON Context Input - Provide context variables in JSON format for expression evaluation
• Instant Results - See evaluation results with type information and error handling
• Automatic Expression Sync - Previewer automatically updates when you edit FEEL files
• Error Feedback - Clear error messages for invalid expressions or context
• Side Panel Integration - Opens conveniently beside your FEEL editor

Commands

Command Palette

• FEEL: Format Document - Format entire FEEL file
• FEEL: Open FEEL Previewer - Open the side previewer panel for expression evaluation

Keyboard Shortcuts

• Shift+Alt+F (Windows/Linux) or Shift+Option+F (macOS) - Format FEEL document (when FEEL file is active)
• Shift+Alt+P (Windows/Linux) or Shift+Option+P (macOS) - Open FEEL Previewer (when FEEL file is active)

Context Menu

• Right-click in FEEL file → Format Document
• Right-click in FEEL file → Open FEEL Previewer

Editor Title Bar

• Click the preview icon (📄) in the editor title bar to open the FEEL Previewer

Using the FEEL Previewer

The FEEL Previewer allows you to test and evaluate FEEL expressions with real context data:

1. Open a FEEL file (.feel extension)
2. Launch the previewer using any of the methods above (Shift+Alt+P, Command Palette, or editor title bar)
3. Enter context data in JSON format in the Context input area
4. Click "Evaluate Expression" to see the result

Example Usage

FEEL Expression (in your .feel file):

if age >= 18 then "adult" else "minor"

Context JSON (in the previewer):

{
  "age": 25,
  "name": "John"
}

Result: "adult"

Advanced Features

• Complex Objects: Test with nested objects, arrays, and complex data structures
• Built-in Functions: Use FEEL functions like now(), date and time(), string(), etc.
• Error Handling: Get clear error messages for invalid expressions or context
• Auto-sync: The previewer automatically updates when you edit your FEEL file

Configuration

{
  "feel.formatting.enable": true,
  "feel.formatting.indentSize": 2,
  "feel.formatting.insertFinalNewline": true,
  "[feel]": {
    "editor.formatOnSave": true
  }
}

File Support

The extension automatically activates for files with .feel extension.

License

This project is licensed under the MIT License.

Copyright (c) 2025 Ahmad Alhowimel