  MLsub is a minimal language with a type system combining subtyping and
parametric polymorphism and a type inference algorithm which infers compact
principal types. Simple-sub is an alternative inference algorithm which can be
implemented efficiently and is easier to understand. MLsub supports explicitly
typed records which are not extensible. Here we extend Simple-sub with
extensible records, meaning that we can add new fields to a previously defined
record. For this we add row variables to our type language and extend the type
constraint solving method of our type inference algorithm accordingly, keeping
the decidability of type inference.
