programming languages

Untyped languages such as JavaScript and Python provide a flexible starting point for software projects, but eventually, the lack of reliable types makes code hard to debug and maintain. Gradually typed languages such as TypeScript, Flow, Mypy, and Pyright address the problem with type checkers that can reason about an ever-growing subset of untyped code.

Gradual typing is a solution to the longstanding tension between typed and untyped languages: let programmers write code in any flexible language (such as Python), equip the language with a suitable type system that can describe invariants in part of a program, and use run-time checks to ensure soundness.