import "lib/mathx.lumen"

// A tiny reverse-polish-notation calculator written in Lumen.
// It tokenizes a space separated expression and folds it over a stack.

fn evalRpn(expression) {
    let tokens = expression.split(" ")
    let stack = []
    for (token in tokens) {
        if (token == "+") {
            let b = stack.pop()
            let a = stack.pop()
            stack.push(a + b)
        } else if (token == "-") {
            let b = stack.pop()
            let a = stack.pop()
            stack.push(a - b)
        } else if (token == "*") {
            let b = stack.pop()
            let a = stack.pop()
            stack.push(a * b)
        } else if (token == "/") {
            let b = stack.pop()
            let a = stack.pop()
            stack.push(a / b)
        } else {
            stack.push(int(token))
        }
    }
    assert(stack.len() == 1, "expression did not reduce to a single value")
    return stack.pop()
}

let expr = "3 4 + 5 * 2 -"
println(expr + " = " + str(evalRpn(expr)))
println("2 3 4 * + = " + str(evalRpn("2 3 4 * +")))
println("10 2 / 3 - = " + str(evalRpn("10 2 / 3 -")))

// factorial and gcd come from the imported module.
println("6! = " + str(factorial(6)))
println("gcd(48, 36) = " + str(gcd(48, 36)))

assert(factorial(5) == 120, "factorial broken")
assert(evalRpn("3 4 +") == 7, "rpn broken")
println("calc checks passed")