Question

I am attempting to pass back a Node type from this function, but I get the error that empty is out of scope:

import Data.Set (Set)  
import qualified Data.Set as Set

data Node = Vertex String (Set Node)  
    deriving Show

toNode :: String -> Node  
toNode x = Vertex x empty

What am I doing wrong?

Answer 1

import qualified Data.Set as Set means that when you want to use something from Data.Set, you have to qualify it with Set.. So to use empty write Set.empty.