A Union in itself is not a sum type. Rust even has unions: https://doc.rust-lang.org/reference/items/unions.html https://doc.rust-lang.org/reference/items/unio

A Union in itself is not a sum type. Rust even has unions: https://doc.rust-lang.org/reference/items/unions.html https://doc.rust-lang.org/reference/items/unions.html The unions of Rust are tagged unions that can hold data: https://doc.rust-lang.org/book/ch06-01-defining-an-enum.html https://doc.rust-lang.org/book/ch06-01-defining-an-enum.html which is immensely powerful in data modeling.