我们可以在Scala中定义更高级别的类型级别的身份功能吗？

The above scoping restrictions are
generalized to the case of nested type
parameter clauses,which declare
higher-order type parameters.
Higher-order type parameters (the type
parameters of a type parameter t ) are
only visible in their immediately
surrounding parameter clause (possibly
including clauses at a deeper nesting
level) and in the bounds of t .
Therefore,their names must only be
pairwise different from the names of
other visible parameters. Since the
names of higher-order type parameters
are thus often irrelevant,they may be
denoted with a ‘_’,which is nowhere
visible.

不久之后,我们讨论了为类型函数添加文字语法的可能性,例如[A] [Int,A].这在Scalaz中真的很有用.在此期间,我们使用Alexey的答案,在PartialApplyXofY traits表达的伎俩.推论会更好,但这是非常棘手,尽管innocuous entry in Trac！)

无论如何,在该线程中,Adriaan mentioned：

It obviously won’t be trivial to
implement everything that logically
follows from having anonymous type
functions,as we currently don’t have
the necessary infrastructure to allow
people to write higher-kinded type
aliases,for example:

type MyTypeFun = [X,Y] Pair[Y,X] //
desirable,but hard to support with
the current implementation (we look at
the type params of a symbol to infer
its kind)

UPDATE

原来你可以很亲密了：

def hk[_[_]] = (); 
hk[({type A[X] = X})#A]

或者有点创意：

def hk[_[_]] = (); hk[({type [X] = X}) #  ]
def hk[_[_]] = (); hk[({type λ[α]=α})#λ ]