A Gradual Type System for Elixir

Abstract

Elixir is a functional programming language with dynamic typing. In this paper we propose a type system that makes it possible to perform static type-checking on a significant fragment of Elixir. An important feature of the type system we introduce is that it does not require any syntactic change to the language. Type information is provided by means of function signatures which are declared in terms of Elixir typespec directives. The proposed type system is based on subtyping and is backward compatible, as it allows the presence of untyped code fragments. We have implemented a prototype of the type-checker in Elixir itself.