  Erlang is a functional programming language with dynamic typing. The language
offers great flexibility for destructing values through pattern matching and
dynamic type tests. Erlang also comes with a type language supporting
parametric polymorphism, equi-recursive types, as well as union and a limited
form of intersection types. However, type signatures only serve as
documentation, there is no check that a function body conforms to its
signature. Set-theoretic types and semantic subtyping fit Erlang's feature set
very well. They allow expressing nearly all constructs of its type language and
provide means for statically checking type signatures. This article brings
set-theoretic types to Erlang and demonstrates how existing Erlang code can be
statically typechecked without or with only minor modifications to the code.
Further, the article formalizes the main ingredients of the type system in a
small core calculus, reports on an implementation of the system, and compares
it with other static typecheckers for Erlang.
