- Add function declarations, calls, and return statements
- Implement lexical scoping with Environment class and closures
- Convert print from statement to standard library function
- Add assert() function to standard library for testing
- Add time() function for microsecond precision benchmarking
- Create StdLib class and BuiltinFunction wrapper for standard library
- Implement first-class functions and higher-order functions
- Add function parameter support (tested up to 100 parameters)
- Support alphanumeric identifiers in variable and function names
- Add underscore support in variable names and identifiers
- Implement string + number and number + string concatenation
- Add boolean + string and string + boolean concatenation
- Support string multiplication (string * number)
- Fix decimal truncation issue by using std::stod for all number parsing
- Add comprehensive number formatting with proper precision handling
- Support huge numbers (epoch timestamps) without integer overflow
- Clean number display (no trailing zeros on integers)
- Add basic error handling with program termination on errors
- Add comprehensive test suite covering all features
- Add escape sequence support (\n, \t, \", \\)
- Add comprehensive documentation and language reference
- Update development roadmap with completed features
