Simple types

The term simple types refer to type systems that support

• ground types
• function types
• (optionally) sum and product types
  and so on.

In particular, simplicity means that the type systems are not dependent.

There is of course a grey area. How many bells and whistles can a type system support and still be simple? For example, are modal type systems still simple? One could answer that positively, as there are modal dependent type theories.