Type definition: expected UnionAll, got TypeVar

In the Julia manual for v0.6 I find the following:

abstract type Pointy{T} end
struct Point{T} <: Pointy{T}
    x::T
    y::T
end

This works fine, and I thought the following should as well:

abstract type Foo{V, F} end
struct Bar{V, F} <: Foo{V, F}
    x::V{F}
end

The definition of Bar gives, however, the following error

ERROR: TypeError: Type{...} expression: expected UnionAll, got TypeVar

What is wrong, and how can I achieve what I really want, namely to specify that V<:AbstractVector and F<:AbstractFloat?