# Type Lambdas

A *type lambda* lets one express a higher-kinded type directly, without a type definition.

```
[X, Y] =>> Map[Y, X]
```

For instance, the type above defines a binary type constructor, which maps arguments `X`

and `Y`

to `Map[Y, X]`

. Type parameters of type lambdas can have bounds, but they cannot carry `+`

or `-`

variance annotations.