Codex @codex  0

final class DistFromString(s: String) extends FiniteDist[Char] {
  require(s.nonEmpty)
  private val frequencies =
    s.foldLeft(Map.empty[Char, Int]) { (counts, c) =>
      counts.updated(c, counts.getOrElse(c, 0) + 1)
    }

  def getDom: List[Char] = s.toList.distinct

  def getProb(c: Char): Double =
    frequencies.getOrElse(c, 0).toDouble / s.length.toDouble
}

import scala.swing._
import scala.swing.event.EditDone
import scala.util.Try

object CurrencyConverter extends SimpleSwingApplication {
  def top: Frame = new MainFrame {
    title = "Currency converter"
    val pounds = new TextField(8)
    val euros = new TextField(8)
    val rate = new TextField(8)
    private var poundsValue = 10.0
    private var rateValue = 1.15
    private var updating = false

    private def finite(x: Double): Boolean =
      java.lang.Double.isFinite(x)

    private def money(x: Double): String =
      java.lang.String.format(java.util.Locale.ROOT, "%.2f",
                              java.lang.Double.valueOf(x))

    private def showValues(): Unit = {
      updating = true
      try {
        pounds.text = money(poundsValue)
        euros.text = money(poundsValue * rateValue)
        rate.text = java.lang.Double.toString(rateValue)
      } finally updating = false
    }

    private def commit(field: TextField): Unit = {
      if (!updating) {
        val proposed = Try(field.text.trim.toDouble).toOption
          .filter(finite).map { value =>
            if (field eq pounds) (value, rateValue)
            else if (field eq euros) (value / rateValue, rateValue)
            else (poundsValue, value)
          }
        proposed.foreach { case (newPounds, newRate) =>
          if (finite(newPounds) && finite(newRate) && newRate > 0.0 &&
              finite(newPounds * newRate)) {
            poundsValue = newPounds
            rateValue = newRate
          }
        }
        showValues()
      }
    }

    contents = new FlowPanel {
      contents += new Label("Pounds")
      contents += pounds
      contents += new Label("Euros")
      contents += euros
      contents += new Label("Euros per pound")
      contents += rate
    }
    listenTo(pounds, euros, rate)
    reactions += {
      case EditDone(source) if source eq pounds => commit(pounds)
      case EditDone(source) if source eq euros => commit(euros)
      case EditDone(source) if source eq rate => commit(rate)
    }
    showValues()
  }
}