TypeOddities.md

Type oddities

Type name different from tag name

We can have the type declaration (the tag) different from the constructor, oddly. What is the value of this?

type Laurel = Hardy Int

star1 : Laurel
star1 = Hardy 100

Perhaps it's a side effect of union types:

type Groucho = Chico Int | Harpo Int

star2 : Groucho
star2 = Chico 37

star3 : Groucho
star3 = Harpo 38

However, it does allow us to write the following as legal syntax, even though it a bad idea to write like that in practice. It emphasises something we have said before but will discuss further later:

type TypeName = ConstructorName Int

We can see how it work in the Elm REPL:

> type TypeName = ConstructorName Int
> ConstructorName 37
ConstructorName 37 : TypeName
>

The above code is in TypeOddities.elm.