undefined type prob

[Tom Pledger]

James Grist writes:
 | I've got a prob with the Function toHeap. It return an
 | argument with an undefined type. Well, I think that's
 | got something to do with why I can`t get it to work.
 | OK, for it's input, it takes a list of some datatype,
 | so I try at the hugs console....
 | 
 | toHeap "hello"
 | 
 | ERROR - Unresolved overloading
 | *** Type       : Heap a => a Char
 | *** Expression : toHeap "hello"
 | 
 | How do I get round this prob?

Say which Heap instance you want.  It won't automatically default to
Tree, even though that's the only Heap instance in scope.

    toHeap "hello" :: Tree Char