Odd failure to deduce a constraint
Using a type family to build a compound constraint that includes several constraints produced by applying another type family results in a type checker error like,
Could not deduce (ConFun l a, ConFun l b)
arising from a use of ‘bar’
from the context (ConFun l a, ConFun l b)
bound by the type signature for
baz :: (ConFun l a, ConFun l b) => Proxy l -> HList '[a, b] -> ()
An example program is given at, https://gist.github.com/acowley/a001bd092599b5914bad
Trac metadata
Trac field | Value |
---|---|
Version | 7.8.3 |
Type | Bug |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | Compiler |
Test case | |
Differential revisions | |
BlockedBy | |
Related | |
Blocking | |
CC | |
Operating system | |
Architecture |