| (* Binary tree with leaves carrying an integer. *) | |
| type tree = Leaf of int | Node of tree * tree | |
| let rec exists_leaf test tree = | |
| match tree with | |
| | Leaf v -> test v | |
| | Node (left, right) -> | |
| exists_leaf test left | |
| || exists_leaf test right | |
| let has_even_leaf tree = | |
| exists_leaf (fun n -> n mod 2 = 0) tree |