Show instance for Digraph.Forest overlaps with Show [a]
Steps to reproduce:
module Foo where
import Digraph ()
newtype MyList a = MyList [a]
deriving Show$ ghci -packageghc Foo.hs
Foo.hs:6:12:
Overlapping instances for Show [a]
arising from the 'deriving' clause of a data type declaration
Matching instances:
instance Show a => Show [a] -- Defined in `GHC.Show'
instance Show a => Show (Digraph.Forest a) -- Defined in `Digraph'
(The choice depends on the instantiation of `a'
To pick the first instance above, use -XIncoherentInstances
when compiling the other instance declarations)
When deriving the instance for (Show (MyList a))
Failed, modules loaded: none.Trac metadata
| Trac field | Value |
|---|---|
| Version | 7.4.1 |
| Type | Bug |
| TypeOfFailure | OtherFailure |
| Priority | normal |
| Resolution | Unresolved |
| Component | GHC API |
| Test case | |
| Differential revisions | |
| BlockedBy | |
| Related | |
| Blocking | |
| CC | |
| Operating system | |
| Architecture |