The type constructor variable "gr" can be instantiated with "Data.Graph.Inductive.Tree.Gr" via a type signature: Prelude Data.Graph.Inductive.Example> ucycle 5 :: Data.Graph.Inductive.Tree.Gr () () 1:()->[((),2)] 2:()->[((),3)] 3:()->[((),4)] 4:()->[((),5)] 5:()->[((),1)] HTH Christian Joe Schafer wrote:

Hey all,

New to Haskell and I'm trying to use the FGL but I keep running into the same error.

If I load Data.Graph.Inductive.Example and use one of the example functions such as ucycle I get:

Ambiguous type variable `gr' in the constraint: `Graph gr' arising from a use of `ucycle' at <interactive>:1:0-7 Probable fix: add a type signature that fixes these type variable(s)

Here's the type of ucycle for reference.

ucycle :: Graph gr => Int -> gr () ()

I'm using GHC 6.10.1 and FGL 5.4.2.2

Thanks, Joe