binary_tree.c

// Sums all nodes of a binary tree.

#include <datatype99.h>

#include <stdio.h>

// clang-format off
datatype(
    BinaryTree,
    (Leaf, int),
    (Node, BinaryTree *, int, BinaryTree *)
);
// clang-format on

int sum(const BinaryTree *tree) {
    match(*tree) {
        of(Leaf, x) return *x;
        of(Node, lhs, x, rhs) return sum(*lhs) + *x + sum(*rhs);
    }

    // Invalid input (no such variant).
    return -1;
}

#define TREE(tree)                ((BinaryTree *)(BinaryTree[]){tree})
#define NODE(left, number, right) TREE(Node(left, number, right))
#define LEAF(number)              TREE(Leaf(number))

int main(void) {
    const BinaryTree *tree = NODE(NODE(LEAF(1), 2, NODE(LEAF(3), 4, LEAF(5))), 6, LEAF(7));

    /*
     * Output:
     * 28
     */
    printf("%d\n", sum(tree));

    return 0;
}