#!/usr/bin/ruby
var AST = Hash(
    self => Number(1),
    call => [
              Hash(method => "add", arg => [Hash(self => Number(2))]),
              Hash(method => "add", arg => [Hash(self => Number(3))]),
            ],
)
func execute(expr) {
    var self_obj = expr{"self"}
    for call in (expr{"call"}) {
         self_obj = self_obj.(call{"method"})(call{"arg"}.map{execute(_)}...)
    }
    return self_obj
}
assert_eq(execute(AST), 6)
say "** Test passed!"