> module Reduce where Two ways to fold ints from the tree defined in > import TreeDatatype > errorMsg = error "PolyP: Reduce test fails for Tree a w datatype." > sizeListTree :: [Tree a w] -> Int > sizeListTree = errorMsg > collectListTree :: [Tree a w] -> [a] > collectListTree = errorMsg > sumListTree :: [Tree Int w] -> Int > sumListTree = errorMsg But note that folding is supported for Regular datatypes.