             print("Tried to lowercase a null string")
             throw ExecErrors.NullPointerError
         }
-        set(variable, value: get(variable)!.lowercaseString)
+        try set(variable, value: get(variable)!.lowercaseString)
         return nil
     }
     

        methods["blackAndWhite"] = blackAndWhite
        methods["toLower"] = toLower
        methods["toUpper"] = toUpper
        methods["toCap"] = toUpper
        // MARK: parse
        var commands: [(Int, String)] = []
        for line in 0..<lines.count {

    var methods: [String: ((String, String) throws -> String?)] = [:]
    var properties: [String: String?] = [:]
    var constants: [String: String?] = [:]
    var baloons: [(UIImage, UIImage, UIImage)] = []
    
    let completeCode: String
    var line = 0
    
    init(dir: String, code: String) throws {
        self.dir = dir
        self.completeCode = code
        let lines = code.componentsSeparatedByString("\n")
        // MARK: constants & default properties
        constants["_PLATFORM_OS"] = "iOS"
