Type families returning quantified types
Is there a fundamental reason for not being able to use quantification in a type family? I'd very much like to be able to do it, obviously turning on RankNTypes if necessary.
I'm looking for things like this:
type family Foo (x :: Bool) where
Foo True = forall a. [a]
Foo False = ()Trac metadata
| Trac field | Value |
|---|---|
| Version | 7.8.2 |
| Type | FeatureRequest |
| TypeOfFailure | OtherFailure |
| Priority | normal |
| Resolution | Unresolved |
| Component | Compiler |
| Test case | |
| Differential revisions | |
| BlockedBy | |
| Related | |
| Blocking | |
| CC | |
| Operating system | |
| Architecture |
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