Change role annotation syntax
Currently, role annotations look like this:
data Foo a@N = ...
I've received several criticisms of this syntax:
- It is not backward compatible. If a library wishes to use role annotations and remain compilable with earlier versions of GHC, preprocessor commands are necessary.
- It is inscrutable for someone not well-versed in roles.
- It reminds people of as-patterns, which it is unrelated to.
- It is conceivable that it would conflict with type-level as-patterns.
For these reasons, I propose the following:
data Foo a {-# ROLE Nominal #-} = ...
This syntax, while verbose, eliminates these concerns, considering that the new syntax is easily searchable for someone who doesn't know it. I have proposed something similar on ghc-devs, with no response, so I will implement it shortly.
Trac metadata
Trac field | Value |
---|---|
Version | 7.7 |
Type | FeatureRequest |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | Compiler |
Test case | |
Differential revisions | |
BlockedBy | |
Related | |
Blocking | |
CC | |
Operating system | |
Architecture |