What are “sums-and-products” data structures?

Question

A recent blog post on William Cook\'s Fusings mentions:

The key point is that structures in Ensō are viewed holistically as graphs, not as individual

Answer 1

He is referring to the standard algebraic data types of functional programming languages.

Examples:

• If a is of type A and b is of type B then (a, b) is of type A x B, which is a product type.

• A list type with values of the form Nil or Cons x xs is a sum type.

Ensō apparently has a greater emphasis on graphs than these tree-like algebraic types.