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 |