Type aliases in arbitrary blocks.

On 2012-01-14 19:23:24 -0600, Aleksey Nikiforov said:

Local type aliases are supported. Double check your signatures.

Any idea why they are not supported at the top level of a package (i.e. without a package object)?

On Sat, Jan 14, 2012 at 6:44 PM, Kris Nuttycombe <kris [dot] nuttycombe [at] gmail [dot] com> wrote:

Hi, all,

As my types become more sophisticated, I find myself really wishing that type aliases could be defined in arbitrary blocks, not just as members of traits, classes, or objects.

As a workaround for this lack, I find myself often writing something like this:

trait Value[A] {

  def value: A

}

def foo: A = new Value[A] {

  type ER[R] = Either[String, R]

  type F[A] = SomeOtherTypeThatTakesATypeConstructorAsItsFirstArg[ER, A]

  val value = { /* use F as a type constructor somewhere in here */ }

}.value

Why is it that local type aliases are not supported, and is there any possibility of adding this feature to the language? I know about the inline type lambda trick, of course, but when you start encountering nested lambdas things get a bit hairy to read. Of course, a better syntax for writing type lambdas would also be desirable, but even in the presence of such a syntax enhancement nested type lambdas would still be less readable than if type aliases could be defined in method bodies (or arbitrary blocks):

def foo: A = {

  type ER[R] = Either[String, R]

  type F[A] = SomeOtherTypeThatTakesATypeConstructorAsItsFirstArg[ER, A]

  // use F as a type constructor

}

Local type aliases are supported. Double check your signatures.


On Sat, Jan 14, 2012 at 6:44 PM, Kris Nuttycombe <kris [dot] nuttycombe [at] gmail [dot] com> wrote:

Hi, all,
As my types become more sophisticated, I find myself really wishing that type aliases could be defined in arbitrary blocks, not just as members of traits, classes, or objects.
As a workaround for this lack, I find myself often writing something like this:
trait Value[A] {  def value: A}
def foo: A = new Value[A] {   type ER[R] = Either[String, R]  type F[A] = SomeOtherTypeThatTakesATypeConstructorAsItsFirstArg[ER, A]    val value = { /* use F as a type constructor somewhere in here */ } }.value
Why is it that local type aliases are not supported, and is there any possibility of adding this feature to the language? I know about the inline type lambda trick, of course, but when you start encountering nested lambdas things get a bit hairy to read. Of course, a better syntax for writing type lambdas would also be desirable, but even in the presence of such a syntax enhancement nested type lambdas would still be less readable than if type aliases could be defined in method bodies (or arbitrary blocks):
def foo: A = {  type ER[R] = Either[String, R]  type F[A] = SomeOtherTypeThatTakesATypeConstructorAsItsFirstArg[ER, A]
  // use F as a type constructor }