Example use case:

caseclass.Sum(“l”, “r”)
caseclass.Var(“n”)
caseclass.Const(“v”)
def evaluate(t, env):
    return t.match(
        case[Sum] >> (lambda l, r: evaluate(l, env) + evaluate(r, env)),
        case[Var] >> (lambda n: env[n]),
        case[Const] >> (lambda v: v),
    )

# Let’s calculate: (x + x) + (7 + y)
tree = Sum(Sum(Var(x), Var(x)), Sum(Const(7), Var(y)))
evaluate(tree, {"x”: 5, "y”: 6}) # == 23