Editing Comparing class alias proposals (section)

== Higher-order context synonyms ==

Possible additions to the context synonyms include:

'''Q''': May a CS's RHS refer to other CS's? For example:

 context Foo a = (BoundedEnum a, Eq a, Ord a)

This introduces the possibility of loops. Should loops be forbidden? It could be argued that in some cases of loops, the CS's transitive closure should be used, but this is only acceptable if the closure is finite. It seems more elegant to just forbid all loops.

'''Q''': Apart from type constructors, may a CS's variables be class constructors (things of kind ... -> Context) as well? For example:

 context Bar a = a Int

Here Bar :: (* -> Context) -> Context

'''Q''': May CS's be passed as arguments to other CS's? For example:

 context Biz = Bar BoundedEnum

'''Q''': May CS's be partially applied? Consider these alternate definitions of BoundedEnum:

 context BoundedEnum a = (Bounded, Enum) a
 context BoundedEnum = (Bounded, Enum)

Currently the <code>,</code> separator can be seen as having kind <code>Context -> Context -> Context</code>, but the example above would make this more generic: <code>k -> k -> k</code>.

'''Motivation''': these ideas are direct extensions of context synonyms and are useful for clients.