[Haskell-cafe] A binary tree
paolo_veronelli at yahoo.it
Sun Jul 4 09:00:20 EDT 2004
I want to build a binary tree where each leaf is a string of "L" and "R"
defining their position from the top
This should be done without context isn't it?
data Tree a = Fork (Tree a) (Tree a) | Leaf a deriving Show
t =Leaf ""
treeGrower :: Tree a -> Tree a
treeGrower (Leaf a )= treeGrower (Fork (Leaf (a++"1")) (Leaf (a++"2")))
treeGrower (Fork l r) = Fork (treeGrower l) (treeGrower r)
Cannot unify the type-signature variable `a' with the type `[a1]'
Expected type: [a1]
Inferred type: a
In the first argument of `(++)', namely `a'
In the first argument of `Leaf', namely `(a ++ "1")'
I don't get it.........
More information about the Haskell-Cafe