Reduce clause

The reduce clause can be used to combine the results of parallel computations into a single value, such as summing partial results from each parallel task into a total.

parallel for t = 0 to (NO_TASKS - 1) reduce(sum: total_check):
    int check = 0
    for i32 j = n; j >= 1; j--:
        ref TreeNode tree = TreeNode::bottom_up_tree(depth)
        check = check + tree.item_check()
    total_check = total_check + check