COOL (Classroom Object-Oriented Language) is a small object-oriented
language used to teach compiler construction. This project builds an
interpreter for it with one big extension: an AUTO_TYPE keyword that lets
programmers omit type annotations and have the interpreter work them out,
the same convenience that powers var in C# or auto in C++.
The inference collects constraints from how each value is used: what a variable starts as, what a function returns, what operations touch an attribute. From those clues the system deduces the most concrete type it can justify. It handles ever harder cases, from simple variable declarations up to recursive functions, and is honest about the limits: some cases, like mutually recursive functions, cannot always be inferred, and the system says so rather than guess.
The interpreter is written in Python and wrapped in a small Flask web interface where you can type COOL programs and watch the inferred types come back.