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 |