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import Foundation | |
class CalculatorBrain | |
{ | |
private enum Op: Printable | |
{ | |
case Operand(Double) | |
case UnaryOperation(String, Double -> Double) | |
case BinaryOperation(String, (Double, Double) -> Double) | |
var description: String { | |
get { | |
switch self { | |
case .Operand(let operand): | |
return "\(operand)" | |
case .UnaryOperation(let symbol, _): | |
return symbol | |
case .BinaryOperation(let symbol, _): | |
return symbol | |
} | |
} | |
} | |
} | |
private var opStack = [Op]() | |
private var knownOps = [String:Op]() | |
init() { | |
func learnOp(op: Op) { | |
knownOps[op.description] = op | |
} | |
knownOps["×"] = Op.BinaryOperation("×", *) | |
knownOps["÷"] = Op.BinaryOperation("÷") { $1 / $0} | |
knownOps["+"] = Op.BinaryOperation("+", +) | |
knownOps["−"] = Op.BinaryOperation("−") { $1 - $0} | |
knownOps["√"] = Op.UnaryOperation("√", sqrt) | |
} | |
private func evaluate(ops: [Op]) -> (result: Double?, remainingOps: [Op]) | |
{ | |
if !ops.isEmpty { | |
var remainingOps = ops | |
let op = remainingOps.removeLast() | |
switch op { | |
case .Operand(let operand): | |
return (operand, remainingOps) | |
case .UnaryOperation(_, let operation): | |
let operandEvaluation = evaluate(remainingOps) | |
if let operand = operandEvaluation.result { | |
return (operation(operand), operandEvaluation.remainingOps) | |
} | |
case .BinaryOperation(_, let operation): | |
let op1Evaluation = evaluate(remainingOps) | |
if let operand1 = op1Evaluation.result { | |
let op2Evaluation = evaluate(op1Evaluation.remainingOps) | |
if let operand2 = op2Evaluation.result { | |
return (operation(operand1, operand2), op2Evaluation.remainingOps) | |
} | |
} | |
} | |
} | |
return (nil, ops) | |
} | |
func evaluate() -> Double? { | |
let (result, remainder) = evaluate(opStack) | |
println("\(opStack) = \(result) with \(remainder) left over") | |
return result | |
} | |
} |
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