Coercible solver incomplete with non-variable transitivity
If I say
import Data.Coerce
import Data.Proxy
foo :: (Coercible (a b) (c d), Coercible (c d) (e f)) => Proxy (c d) -> a b -> e f
foo _ = coerce
I get an error, because GHC isn't smart enough to figure out transitivity in this case. It can do it with bare variables, but not variable applications. It's possible there's a way to do this, but we'll wait for someone to shout before investing effort.
Do shout if this lack of functionality is ruining your day!
Trac metadata
Trac field | Value |
---|---|
Version | 7.11 |
Type | Bug |
TypeOfFailure | OtherFailure |
Priority | low |
Resolution | Unresolved |
Component | Compiler |
Test case | |
Differential revisions | |
BlockedBy | |
Related | |
Blocking | |
CC | |
Operating system | |
Architecture |