object solver extends Application {
 trait Constraint {
 def newValue: unit;
 def dropValue: unit
 }
 
 object NoConstraint extends Constraint {
 def newValue: unit = error("NoConstraint.newValue");
 def dropValue: unit = error("NoConstraint.dropValue");
 }
 
 case class Adder(a1: Quantity, a2: Quantity, sum: Quantity) extends Constraint {
 def newValue: unit = Triple(a1.getValue, a2.getValue, sum.getValue) match {
 case Triple(Some(x1), Some(x2), _ ) => sum.setValue(x1 + x2, this)
 case Triple(Some(x1), _ , Some(r)) => a2.setValue(r - x1, this)
 case Triple(_ , Some(x2), Some(r)) => a1.setValue(r - x2, this)
 case _ => ()
 }
 def dropValue: unit = {
 a1.forgetValue(this); a2.forgetValue(this); sum.forgetValue(this);
 }
 a1 connect this;
 a2 connect this;
 sum connect this;
 }
 case class Constant(q: Quantity, v: double) extends Constraint {
 def newValue: unit = error("Constant.newValue");
 def dropValue: unit = error("Constant.dropValue");
 q connect this;
 q.setValue(v, this);
 }
 case class Probe(name: String, q: Quantity) extends Constraint {
 def newValue: unit = printProbe(q.getValue);
 def dropValue: unit = printProbe(None);
 private def printProbe(v: Option[double]): unit = {
 val vstr = v match {
 case Some(x) => x.toString()
 case None => "?"
 }
 Console.println("Probe: " + name + " = " + vstr);
 }
 q connect this
 }
 
 // COMPLETE HERE: define constraints for multiplication, equality and square.
 
 class Quantity {
 
 private var value: Option[double] = None;
 private var constraints: List[Constraint] = List();
 private var informant: Constraint = null;
 
 def getValue: Option[double] = value;
 
 def setValue(v: double, setter: Constraint): unit = value match {
 case Some(v1) =>
 if (v != v1) error("Error! contradiction: " + v + " and " + v1);
 case None => {
 informant = setter;
 value = Some(v);
 for (val c <- constraints; c != informant) c.newValue; } } def setValue(v: double): unit = setValue(v, NoConstraint); def forgetValue(retractor: Constraint): unit = { if (retractor == informant) { value = None; for (val c <- constraints; c != informant) c.dropValue; } } def forgetValue: unit = forgetValue(NoConstraint); def connect(c: Constraint): unit = { constraints = c :: constraints; value match { case Some(_) => c.newValue
 case None => ()
 }
 }
 
 def +(that: Quantity): Quantity = {
 val sum = new Quantity;
 Adder(this, that, sum);
 sum
 }
 
 // COMPLETE HERE: define operators "*" and "===". 
 
 override def toString(): String = value match {
 case None => " ?"
 case Some(v) => v.toString()
 }
 }
 // COMPLETE HERE: define a function "c" that creates a constant quantity.
 
 def adderExample = {
 val q1, q2, q3 = new Quantity;
 Adder(q1, q2, q3);
 Probe("q1", q1);
 Probe("q2", q2);
 Probe("q3", q3);
 
 q1.setValue(20);
 q2.setValue(22);
 q1.forgetValue;
 q2.forgetValue;
 Console.println("-----");
 
 q1.setValue(20);
 q3.setValue(22);
 q1.forgetValue;
 q3.forgetValue;
 Console.println("-----");
 
 q2.setValue(20);
 q3.setValue(22);
 q2.forgetValue;
 q3.forgetValue;
 Console.println("-----");
 }
 
 def converterExample = {
 // COMPLETE HERE: write the Celsius/Fahrenheit converter.
 }
 
 adderExample;
 converterExample;
}
</div><div class="naked_ctrl">
<form action="/index.cgi/larger-text" method="get" name="gate">
<p><a href="http://altstyle.alfasado.net">AltStyle</a> によって変換されたページ <a href="http://lampwww.epfl.ch/teaching/archive/programmation_4/2006/exercises/week11/solver-partial.scala">(-&gt;オリジナル)</a>
/ <label>アドレス: <input type="text" name="naked_post_url" value="http://lampwww.epfl.ch/teaching/archive/programmation_4/2006/exercises/week11/solver-partial.scala" size="22" /></label> <label>モード: <select name="naked_post_mode">
<option value="default">デフォルト</option>
<option value="speech">音声ブラウザ</option>
<option value="ruby">ルビ付き</option>
<option value="contrast">配色反転</option>
<option value="larger-text" selected="selected">文字拡大</option>
<option value="mobile">モバイル</option>
</select>
<input type="submit" value="表示" />
</p>
</form>
</div>