Progressions of Concision

Let's take a contrasting look at the complexity of implementing data structures in different languages.

Disjunction

Let's implement a simple sum type, Either, in a few polymorphic languages.

Composable disjunction

Either is useful for storing a value of one of two types, but it isn't useful for building up behavior from multiple disjunctions.

Let's make it composable by adding map, ap, and flatMap (a.k.a. fmap, <*>, and >>=), and biasing it to the right.