Sample run of chapter's interpreter examples
// In file mutable-objects/Ex1.scala val cs = List('a', 'b', 'c')
// In file mutable-objects/Ex2.scala class BankAccount { private var bal: Int = 0 def balance: Int = bal def deposit(amount: Int) = { require(amount > 0) bal += amount } def withdraw(amount: Int): Boolean = if (amount > bal) false else { bal -= amount true } }
scala> val account = new BankAccount account: BankAccount = BankAccount@d504137 scala> account deposit 100 scala> account withdraw 80 res1: Boolean = true scala> account withdraw 80 res2: Boolean = false
// In file mutable-objects/Ex3.scala class Keyed { def computeKey: Int = ... // this will take some time ... }
// In file mutable-objects/Ex3.scala class MemoKeyed extends Keyed { private var keyCache: Option[Int] = None override def computeKey: Int = { if (!keyCache.isDefined) keyCache = Some(super.computeKey) keyCache.get } }
var hour = 12
// In file mutable-objects/Ex4.scala class Time { var hour = 12 var minute = 0 }
// In file mutable-objects/Ex5.scala class Time { private[this] var h = 12 private[this] var m = 0 def hour: Int = h def hour_=(x: Int) = { h = x } def minute: Int = m def minute_=(x: Int) = { m = x } }
// In file mutable-objects/Ex6.scala class Time { private[this] var h = 12 private[this] var m = 0 def hour: Int = h def hour_= (x: Int) = { require(0 <= x && x < 24) h = x } def minute = m def minute_= (x: Int) = { require(0 <= x && x < 60) m = x } }
// In file mutable-objects/Ex7.scala class Thermometer { var celsius: Float = _ def fahrenheit = celsius * 9 / 5 + 32 def fahrenheit_= (f: Float) = { celsius = (f - 32) * 5 / 9 } override def toString = s"{fahrenheit}F/{celsius}C" }
var celsius: Float
scala> val t = new Thermometer t: Thermometer = 32.0F/0.0C scala> t.celsius = 100 mutated t.celsius scala> t res3: Thermometer = 212.0F/100.0C scala> t.fahrenheit = -40 mutated t.fahrenheit scala> t res4: Thermometer = -40.0F/-40.0C
val a = new Wire val b = new Wire val c = new Wire
val a, b, c = new Wire
def inverter(input: Wire, output: Wire) def andGate(a1: Wire, a2: Wire, output: Wire) def orGate(o1: Wire, o2: Wire, output: Wire)
// In file mutable-objects/Simulator2.scala def halfAdder(a: Wire, b: Wire, s: Wire, c: Wire) = { val d, e = new Wire orGate(a, b, d) andGate(a, b, c) inverter(c, e) andGate(d, e, s) }
// In file mutable-objects/Simulator2.scala def fullAdder(a: Wire, b: Wire, cin: Wire, sum: Wire, cout: Wire) = { val s, c1, c2 = new Wire halfAdder(a, cin, s, c1) halfAdder(b, s, sum, c2) orGate(c1, c2, cout) }
// In file mutable-objects/Simulator1.scala abstract class Simulation { type Action = () => Unit case class WorkItem(time: Int, action: Action) private var curtime = 0 def currentTime: Int = curtime private var agenda: List[WorkItem] = List() private def insert(ag: List[WorkItem], item: WorkItem): List[WorkItem] = { if (ag.isEmpty || item.time < ag.head.time) item :: ag else ag.head :: insert(ag.tail, item) } def afterDelay(delay: Int)(block: => Unit) = { val item = WorkItem(currentTime + delay, () => block) agenda = insert(agenda, item) } private def next() = { (agenda: @unchecked) match { case item :: rest => agenda = rest curtime = item.time item.action() } } def run() = { afterDelay(0) { println("*** simulation started, time = " + currentTime + " ***") } while (!agenda.isEmpty) next() } }
// In file mutable-objects/Simulator2.scala type Action = () => Unit
// In file mutable-objects/Simulator2.scala private var curtime: Int = 0
// In file mutable-objects/Simulator2.scala def currentTime: Int = curtime
// In file mutable-objects/Simulator2.scala case class WorkItem(time: Int, action: Action)
// In file mutable-objects/Simulator2.scala private var agenda: List[WorkItem] = List()
// In file mutable-objects/Simulator2.scala def afterDelay(delay: Int)(block: => Unit) = { val item = WorkItem(currentTime + delay, () => block) agenda = insert(agenda, item) }
afterDelay(delay) { count += 1 }
private def insert(ag: List[WorkItem], item: WorkItem): List[WorkItem] = { if (ag.isEmpty || item.time < ag.head.time) item :: ag else ag.head :: insert(ag.tail, item) }
// In file mutable-objects/Simulator2.scala def run() = { afterDelay(0) { println("*** simulation started, time = " + currentTime + " ***") } while (!agenda.isEmpty) next() }
// In file mutable-objects/Simulator2.scala private def next() = { (agenda: @unchecked) match { case item :: rest => agenda = rest curtime = item.time item.action() } }
Simulator.scala:19: warning: match is not exhaustive! missing combination Nil agenda match { ^ one warning found
// In file mutable-objects/Simulator1.scala package org.stairwaybook.simulation abstract class BasicCircuitSimulation extends Simulation { def InverterDelay: Int def AndGateDelay: Int def OrGateDelay: Int class Wire { private var sigVal = false private var actions: List[Action] = List() def getSignal = sigVal def setSignal(s: Boolean) = if (s != sigVal) { sigVal = s actions foreach (_ ()) } def addAction(a: Action) = { actions = a :: actions a() } } def inverter(input: Wire, output: Wire) = { def invertAction() = { val inputSig = input.getSignal afterDelay(InverterDelay) { output setSignal !inputSig } } input addAction invertAction } // continued in Listing 18.10...
// In file mutable-objects/Simulator1.scala // ...continued from Listing 18.9 def andGate(a1: Wire, a2: Wire, output: Wire) = { def andAction() = { val a1Sig = a1.getSignal val a2Sig = a2.getSignal afterDelay(AndGateDelay) { output setSignal (a1Sig & a2Sig) } } a1 addAction andAction a2 addAction andAction } def orGate(o1: Wire, o2: Wire, output: Wire) = { def orAction() = { val o1Sig = o1.getSignal val o2Sig = o2.getSignal afterDelay(OrGateDelay) { output setSignal (o1Sig | o2Sig) } } o1 addAction orAction o2 addAction orAction } def probe(name: String, wire: Wire) = { def probeAction() = { println(name + " " + currentTime + " new-value = " + wire.getSignal) } wire addAction probeAction } }
// In file mutable-objects/Simulator2.scala class Wire { private var sigVal = false private var actions: List[Action] = List() def getSignal = sigVal def setSignal(s: Boolean) = if (s != sigVal) { sigVal = s actions foreach (_ ()) } def addAction(a: Action) = { actions = a :: actions a() } }
// In file mutable-objects/Simulator2.scala def inverter(input: Wire, output: Wire) = { def invertAction() = { val inputSig = input.getSignal afterDelay(InverterDelay) { output setSignal !inputSig } } input addAction invertAction }
// In file mutable-objects/Simulator2.scala def andGate(a1: Wire, a2: Wire, output: Wire) = { def andAction() = { val a1Sig = a1.getSignal val a2Sig = a2.getSignal afterDelay(AndGateDelay) { output setSignal (a1Sig & a2Sig) } } a1 addAction andAction a2 addAction andAction }
// In file mutable-objects/Simulator2.scala def probe(name: String, wire: Wire) = { def probeAction() = { println(name + " " + currentTime + " new-value = " + wire.getSignal) } wire addAction probeAction }
// In file mutable-objects/Simulator1.scala package org.stairwaybook.simulation abstract class CircuitSimulation extends BasicCircuitSimulation { def halfAdder(a: Wire, b: Wire, s: Wire, c: Wire) = { val d, e = new Wire orGate(a, b, d) andGate(a, b, c) inverter(c, e) andGate(d, e, s) } def fullAdder(a: Wire, b: Wire, cin: Wire, sum: Wire, cout: Wire) = { val s, c1, c2 = new Wire halfAdder(a, cin, s, c1) halfAdder(b, s, sum, c2) orGate(c1, c2, cout) } }
scala> import org.stairwaybook.simulation._ import org.stairwaybook.simulation._
scala> object MySimulation extends CircuitSimulation { | def InverterDelay = 1 | def AndGateDelay = 3 | def OrGateDelay = 5 | } defined module MySimulation
scala> import MySimulation._ import MySimulation._
scala> val input1, input2, sum, carry = new Wire input1: MySimulation.Wire = BasicCircuitSimulation$Wire@111089b input2: MySimulation.Wire = BasicCircuitSimulation$Wire@14c352e sum: MySimulation.Wire = BasicCircuitSimulation$Wire@37a04c carry: MySimulation.Wire = BasicCircuitSimulation$Wire@1fd10fa scala> probe("sum", sum) sum 0 new-value = false scala> probe("carry", carry) carry 0 new-value = false
scala> halfAdder(input1, input2, sum, carry)
scala> input1 setSignal true scala> run() *** simulation started, time = 0 *** sum 8 new-value = true scala> input2 setSignal true scala> run() *** simulation started, time = 8 *** carry 11 new-value = true sum 15 new-value = false
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