FAWK: LLMs can write a language interpreter

A developer attempting Advent of Code with AWK found it lacked functional programming features like immutability and lexical scope. Using Cursor Agent and Sonnet 4.5, they created FAWK, a functional AWK variant with modern language features. The LLM successfully built a working interpreter with comprehensive tests, demonstrating impressive capability in handling complex language design including closures and multi-dimensional arrays.