# Types

Wipple has a powerful static type system that works similarly to Haskell’s. In short, every expression has a type, which can be expressed using the `::`

operator (pronounced *“is a”*):

```
42 :: Number -- "42 is a number"
"Hello" :: Text
'(1 2 3) :: List Number
x -> x :: Number -> Number
```

You can also create your own types with `type`

:

```
Name : type Text
Person : type {
name :: Name
age :: Number
}
Color : type {
Red
Orange
Yellow
Green
Blue
Purple
}
Maybe-Number : type {
Some Number
None
}
```

By convention, variables representing types and variants of enums are capitalized.

The `Maybe-Number`

type above can be made more general using type functions, which use a `=>`

arrow:

```
Maybe : A => type {
Some A
None
}
```

This also works on other values, like regular functions:

```
it :: A => A -> A
it : x -> x
```

By convention, generic types are named `A`

, `B`

, `C`

, etc., but you should try to give a more specific name if applicable.

Finally, you can use an underscore (`_`

) to represent a placeholder type:

```
Identity : A => -> type (A -> A)
(x :: Number) -> x :: Identity _ -- inferred as Identity Number
```