Allow an injective type family RHS to be another injective type family
Example use case:
{-# LANGUAGE TypeFamilies, TypeFamilyDependencies, UndecidableInstances #-}
type family Foo a = r | r -> a where
Foo Int = Char
Foo Integer = String
type family Bar a = r | r -> a where
Bar Char = Double
Bar String = Float
type family Baz a = r | r -> a where
Baz x = Bar (Foo x)- 0 says:
test.hs:12:9: error:
• Type family equation violates injectivity annotation.
RHS of injective type family equation cannot be a type family:
Baz x = Bar (Foo x) -- Defined at test.hs:12:9
• In the equations for closed type family ‘Baz’
In the type family declaration for ‘Baz’Trac metadata
| Trac field | Value |
|---|---|
| Version | 8.0.1 |
| Type | FeatureRequest |
| TypeOfFailure | OtherFailure |
| Priority | normal |
| Resolution | Unresolved |
| Component | Compiler (Type checker) |
| Test case | |
| Differential revisions | |
| BlockedBy | |
| Related | |
| Blocking | |
| CC | |
| Operating system | |
| Architecture |