IDE Support

Fun provides excellent IDE support through a VS Code extension and Language Server Protocol (LSP) implementation.

Table of Contents

VS Code Extension

The Fun VS Code extension provides a complete development environment for the Fun programming language.

Features

Extension Structure

vscode/
├── client/              # VS Code extension client
│   ├── src/
│   │   └── extension.ts # Main extension code
│   ├── package.json     # Extension manifest
│   └── tsconfig.json    # TypeScript configuration
├── package.json         # Workspace configuration
└── README.md           # Extension documentation

Language Server Protocol

The Fun LSP server provides language intelligence features that work with any LSP-compatible editor.

LSP Features

Starting the LSP Server

# Start LSP server directly
./fun lsp

# The server runs on stdio and communicates with the client

Features

Syntax Highlighting

The extension provides syntax highlighting for:

IntelliSense

Code Completion

# Type to see suggestions
inc = \x -> x + 1
inc(  # Shows parameter hints

Hover Information

# Hover over functions to see types
inc = \x -> x + 1
# Hover over 'inc' shows: Lam<Int, Int>

# Hover over variables
name = "Alice"
# Hover over 'name' shows: Str

Go to Definition

# Right-click on function name
import math from `./math`
math.inc(5)  # Go to definition of 'inc' in math.fun

Error Reporting

Syntax Errors

# Missing semicolon
when x == 0 is
    True -> 1
    False -> 2  # Error: missing semicolon

# Invalid syntax
inc = \x -> x +  # Error: incomplete expression

Type Errors

# Type mismatch
inc = \x -> x + 1
inc(5, 3)  # Error: too many arguments

# Undefined variable
result = undefined_var  # Error: undefined variable

Import Errors

# Missing module
import missing from `./missing`  # Error: module not found

# Invalid import path
import lib from `invalid/path`   # Error: cannot read module

Installation

Building the Extension

  1. Build the Fun executable: 
    go build
  2. Open the extension directory: 
    cd vscode
code .  # Opens VS Code in the extension directory
  3. Install dependencies: 
    npm install
  4. Run the extension:
    • Press F5 in VS Code
    • This opens a new Extension Development Host window
    • Open a .fun file to test the extension

Installing in VS Code

  1. Package the extension: 
    cd vscode
vsce package
  2. Install the extension:
    • In VS Code, go to Extensions (Ctrl+Shift+X)
    • Click “Install from VSIX…”
    • Select the generated .vsix file

Manual Installation

  1. Copy the extension: 
    cp -r vscode ~/.vscode/extensions/fun-language
  2. Restart VS Code:
    • Close and reopen VS Code
    • The extension should be available

Configuration

Extension Settings

Add these settings to your VS Code settings:

{
  "fun.languageServerPath": "/path/to/your/fun",
  "fun.enableTypeChecking": true,
  "fun.showTypeInformation": true,
  "fun.enableCompletion": true
}

Language Configuration

The extension includes language configuration for:

Keybindings

Default keybindings:

Troubleshooting

Common Issues

Extension Not Loading

# Check if the Fun executable is built
ls -la fun

# Verify the extension path in settings
# Make sure fun.languageServerPath points to the correct executable

LSP Server Not Starting

# Test the LSP server manually
./fun lsp

# Check for error messages
# Common issues:
# - Executable not found
# - Permission denied
# - Missing dependencies

No Syntax Highlighting

  1. Check file association:
    • Make sure .fun files are associated with Fun language
    • Right-click on a .fun file → “Open With” → “Fun”
  2. Reload the extension:
    • Press Ctrl+Shift+P
    • Type “Developer: Reload Window”

No IntelliSense

  1. Check LSP connection:
    • Open Output panel (View → Output)
    • Select “Fun Language Server” from dropdown
    • Look for connection errors
  2. Verify file structure:
    • Make sure your .fun files are valid
    • Check for syntax errors that might prevent analysis

Debug Mode

Enable debug mode for detailed logging:

{
  "fun.debug": true,
  "fun.trace": "verbose"
}

Manual LSP Testing

Test the LSP server manually:

# Start server
./fun lsp

# In another terminal, send LSP messages
echo '{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"processId":123,"rootUri":"file:///tmp","capabilities":{}}}' | ./fun lsp

Advanced Configuration

Custom LSP Settings

Configure LSP features:

{
  "fun.lsp": {
    "completion": {
      "triggerCharacters": [".", "("]
    },
    "hover": {
      "enabled": true
    },
    "diagnostics": {
      "enabled": true,
      "delay": 1000
    }
  }
}

Workspace Settings

Project-specific settings in .vscode/settings.json:

{
  "fun.languageServerPath": "./fun",
  "fun.workspaceRoot": ".",
  "fun.includePaths": ["./src", "./lib"]
}

Extension Development

For developers working on the extension:

# Install development dependencies
cd vscode
npm install

# Run tests
npm test

# Build extension
npm run compile

# Package for distribution
vsce package

Best Practices

File Organization

project/
├── src/
│   ├── main.fun
│   ├── math.fun
│   └── utils.fun
├── .vscode/
│   └── settings.json
└── fun  # Executable

Extension Usage

  1. Use type annotations for better IntelliSense
  2. Organize code in modules for better navigation
  3. Use consistent naming for better completion
  4. Enable error reporting to catch issues early

Performance Tips

  1. Keep files small for faster analysis
  2. Use modules to organize large codebases
  3. Avoid circular dependencies that slow down analysis
  4. Use type annotations to reduce inference time

The IDE support provides a professional development experience for Fun programming, with features comparable to mainstream programming languages.