warning for unused type variables in instance contexts; -fwarn-unreachable-type-variables?
I just spend 90 minutes tracking down what ended up being a typo introduced via find-and-replace.
I accidentally introduced a spurious constraint on an instance context:
instance (Monoid m, Context t) => Class t where …I would like to be warned about constraints on variables that certainly have no connection to variables in the instance head. -fwarn-unreachable-type-variables?
This might also help catch those signatures where all occurrences of type variable are as index arguments to a type family, rendering the functional unusable because of "ambiguous type variable" errors at every call site.
Trac metadata
| Trac field | Value |
|---|---|
| Version | 7.6.1 |
| Type | FeatureRequest |
| TypeOfFailure | OtherFailure |
| Priority | normal |
| Resolution | Unresolved |
| Component | Compiler (Type checker) |
| Test case | |
| Differential revisions | |
| BlockedBy | |
| Related | |
| Blocking | |
| CC | |
| Operating system | |
| Architecture |