Add tacopy playground interface

[simonw]

A browser-based playground for the tacopy library's tail-call optimization.
Uses Pyodide to run Python in the browser and shows real-time transformed
code as users type. Includes example functions and helpful error messages
for invalid (non-tail-recursive) code.

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Clone https://github.com/raaidrt/tacopy into /tmp and consult the README

Build a playground interface for this library’s show_transformed_code() function - use can enter Python code in a text area, the function runs on any changes to that text area and updates either an error message or a second texarea showing the converted code

The tacopy-playground.html file should use pyodide and should install tacopy-optimization using micropip

[claude]

Claude finished @simonw's task —— View job

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PR Review: Tacopy Playground Interface

Todo List:

• Check for repository-specific guidelines (CLAUDE.md)
• Read and analyze tacopy-playground.html file
• Review code quality and best practices
• Identify potential bugs or issues
• Assess performance considerations
• Check for security concerns
• Evaluate test coverage needs
• Provide constructive feedback summary

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Code Review Summary

This is a well-crafted, single-page application that creates an interactive playground for the tacopy library. The implementation demonstrates solid frontend development practices with a clean, responsive design.

✅ Strengths

1. Clean Architecture: Single HTML file with embedded CSS and JavaScript keeps everything self-contained
2. Responsive Design: Grid layout with mobile breakpoint at 900px ensures good UX across devices
3. User Experience: Real-time code transformation with debounced input (300ms) prevents excessive API calls
4. Error Handling: Comprehensive error catching with user-friendly error messages
5. Visual Design: Professional dark theme with clear status indicators and syntax highlighting

🔍 Code Quality & Best Practices

Good:

• Modern CSS Grid layout with fallback
• Semantic HTML structure
• Proper error boundaries and user feedback
• Clean separation of concerns within the constraints of a single file

Could Improve:

• Consider extracting CSS and JS into separate files for maintainability (tacopy-playground.html:7-180, 227-415)
• Add input validation before sending to Pyodide
• Consider using TypeScript for better type safety

⚠️ Potential Issues

1. CDN Dependency Risk (tacopy-playground.html:226)

   <script src="https://cdn.jsdelivr.net/pyodide/v0.24.1/full/pyodide.js"></script>

   • Single point of failure if CDN is down
   • Consider adding fallback or self-hosting option

2. Input Sanitization (tacopy-playground.html:361-369)

   const escapedSource = source
       .replace(/\\/g, '\\\\')
       .replace(/"""/g, '\\"\\"\\"')
       .replace(/\n/g, '\\n');

   • Basic escaping but could be more robust
   • Consider using a proper string escaping library

3. Error Message Parsing (tacopy-playground.html:374-391)

   • Regex-based error extraction could be brittle if error formats change
   • Consider more structured error handling

🚀 Performance Considerations

Good:

• Debounced input prevents excessive transformations
• Lazy loading of Pyodide only when needed
• Efficient DOM updates

Could Optimize:

• Add loading states during transformation
• Consider web worker for heavy computations if needed
• Cache transformed results for repeated inputs

🔒 Security Concerns

Low Risk but Consider:

1. Code Execution: While sandboxed in Pyodide, still executing arbitrary Python code
2. XSS Prevention: escapeHtml() function provides basic protection (tacopy-playground.html:394-398)
3. Content Security Policy: Consider adding CSP headers for additional security

🧪 Test Coverage

Currently Missing:

• Unit tests for transformation logic
• Integration tests for Pyodide interaction
• Error handling tests
• UI interaction tests

Recommendations:

• Add Jest/Vitest for JavaScript testing
• Consider Playwright for E2E testing
• Mock Pyodide for unit testing the transformation wrapper

📝 Specific Code Suggestions

1. Add input validation before transformation:

   if (source.length > 10000) {
       outputEl.innerHTML = '<div class="error-message">Code too long (max 10,000 characters)</div>';
       return;
   }

2. Improve error handling robustness:

   // Instead of regex parsing, consider structured error handling
   const parseError = (error) => {
       if (error.name === 'PythonError') {
           return error.message.split('\n')[0]; // First line usually most relevant
       }
       return error.message;
   };

3. Add loading indicator during transformation:

   outputEl.innerHTML = '<span style="color: #888;">Transforming...</span>';

🎯 Overall Assessment

This is a high-quality implementation that successfully demonstrates the tacopy library's capabilities. The code is clean, functional, and user-friendly. The main areas for improvement are around robustness (error handling, input validation) and testability rather than fundamental architectural issues.

Recommendation: Approve with minor suggestions - This adds genuine value to the tacopy ecosystem and is ready for use as-is, with the suggested improvements being nice-to-haves rather than blockers.