Being instance of Monoid is not checked
It is possible pass not only instances of Monoid to tell function and load the file with GHCi. GHCi shows type f :: (MonadWriter ((a -> b) -> [a] -> [b]) m) => t -> m ()
f _ = tell mapHowever, if code is
f = tell mapGHCi shows type error(no instance) as expected.
It seems very strange that type correctness depends on number of parameters for function that is not used anywhere.
Trac metadata
| Trac field | Value |
|---|---|
| Version | 6.10.3 |
| Type | Bug |
| TypeOfFailure | OtherFailure |
| Priority | normal |
| Resolution | Unresolved |
| Component | Compiler (Type checker) |
| Test case | |
| Differential revisions | |
| BlockedBy | |
| Related | |
| Blocking | |
| CC | |
| Operating system | |
| Architecture |