Alias to type lambda cannot be used without application

[s5bug]

Compiler version

3.2.0, 3.2.1-RC2, 3.2.1

Minimized code

type →[-L <: AnyKind, +R <: AnyKind] = [_ <: L] =>> R

type F = Any → Any

Output

-- Error: ----------------------------------------------------------------------
1 |type F = Any → Any
  |         ^^^^^^^^^
  |         type → takes type parameters

Expectation

Scala allows this usage, especially in the context of

trait Free[F <: ((Any → Any) → Any), A]

where

trait Free[F <: /* giant mess of equivalent type lambda */, A]

is equivalent and does compile.

[smarter]

I'm moving this to feature-request because this was an intentional change, although it could change back again as discussed in #9090

[s5bug]

As a question, why does the current error appear at usage and not at declaration?

[smarter]

You mean, why is there no error in the definition of type → ? Because it defines a type lambda which is allowed, you can also write:

type F = [X] =>> (Any → Any)[X]

But the eta-expansion is not performed automatically by the compiler