"Here's a small example showing most of Lily's features:
var math_ops = ["+" => (|a: Integer, b: Integer| a + b),
"-" => (|a, b| a - b),
"*" => (|a, b| a * b),
"/" => (|a, b| a / b)]
define rpn(input: String): Result[String, List[Integer]]
{
var values = input.split(" ").reject(|r| r.is_space() )
var stack: List[Integer] = []
for i in 0...values.size() - 1: {
var v = values[i]
match v.parse_i(): {
case Some(number):
stack.push(number)
case None:
if stack.size() < 2: {
return Failure("Stack underflow.")
}
var right = stack.pop()
var left = stack.pop()
try: {
var op_fn = math_ops[v]
var op_value = op_fn(left, right)
stack.push(op_value)
except KeyError:
return Failure("Invalid operation {0}.".format(v))
except DivisionByZeroError:
return Failure("Attempt to divide by zero.")
}
}
}
return Success(stack)
}
print("1 2 3 4 * + -" |> rpn) # Success([-13])
print("2 2 2 2 * *" |> rpn) # Success([2, 8])
print("*" |> rpn) # Failure("Stack underflow.")
print("1 2 ?" |> rpn) # Failure("Invalid operation ?.")
Last modified 16 December 2024