  Elixir is a functional programming language with dynamic typing. We propose a
gradual type system that makes it possible to perform type-checking on a
significant fragment of the language. An important feature of the type system
is that it does not require any syntactic change to Elixir. 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.
