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35 The SCells Spreadsheet

35.1 The visual framework

// In file scells/ex1/Spreadsheet.scala

  package org.stairwaybook.scells
  import swing._

  class Spreadsheet(val height: Int, val width: Int) 
      extends ScrollPane {

    val table = new Table(height, width) {
      rowHeight = 25
      autoResizeMode = Table.AutoResizeMode.Off
      showGrid = true
      gridColor = new java.awt.Color(150, 150, 150)
    }

    val rowHeader = 
      new ListView((0 until height) map (_.toString)) {
        fixedCellWidth = 30
        fixedCellHeight = table.rowHeight
      }

    viewportView = table
    rowHeaderView = rowHeader
  }


// In file scells/ex5/Main.scala

  package org.stairwaybook.scells
  import swing._

  object Main extends SimpleGUIApplication {
    def top = new MainFrame {
      title = "ScalaSheet"
      contents = new Spreadsheet(100, 26)
    }
  }


  

35.2 Disconnecting data entry and display

// In file scells/ex2/Spreadsheet.scala

  package org.stairwaybook.scells
  import swing._

  class Spreadsheet(val height: Int, val width: Int) 
      extends ScrollPane {

    val cellModel = new Model(height, width)
    import cellModel._
    
    val table = new Table(height, width) {

      // settings as before... 

      override def rendererComponent(isSelected: Boolean,
          hasFocus: Boolean, row: Int, column: Int): Component =

        if (hasFocus) new TextField(userData(row, column))
        else
          new Label(cells(row)(column).toString) { 
            xAlignment = Alignment.Right 
          }

      def userData(row: Int, column: Int): String = {
        val v = this(row, column)
        if (v == null) "" else v.toString
      }
    }
    // rest as before... 
  } 


// In file scells/ex3/Model.scala

  package org.stairwaybook.scells

  class Model(val height: Int, val width: Int) { 

    case class Cell(row: Int, column: Int)

    val cells = new Array[Array[Cell]](height, width) 

    for (i <- 0 until height; j <- 0 until width) 
      cells(i)(j) = new Cell(i, j)
  }


  

35.3 Formulas

// In file scells/ex5/Formulas.scala

  package org.stairwaybook.scells

  trait Formula  

  case class Coord(row: Int, column: Int) extends Formula {
    override def toString = ('A' + column).toChar.toString + row
  }
  case class Range(c1: Coord, c2: Coord) extends Formula {
    override def toString = c1.toString +":"+ c2.toString
  }
  case class Number(value: Double) extends Formula {
    override def toString = value.toString 
  }
  case class Textual(value: String) extends Formula { 
    override def toString = value
  }
  case class Application(function: String, 
      arguments: List[Formula]) extends Formula { 

    override def toString = 
      function + arguments.mkString("(", ",", ")")
  }
  object Empty extends Textual("")


  

35.4 Parsing formulas

// In file scells/ex5/FormulaParsers.scala

  package org.stairwaybook.scells
  import scala.util.parsing.combinator._

  object FormulaParsers extends RegexParsers { 


// In file scells/ex5/FormulaParsers.scala

    def ident: Parser[String] = """[a-zA-Z_]\w*""".r
    def decimal: Parser[String] = """-?\d+(\.\d*)?""".r


// In file scells/ex5/FormulaParsers.scala

    def cell: Parser[Coord] = 
      """[A-Za-z]\d+""".r ^^ { s => 
        val column = s.charAt(0).toUpper - 'A'
        val row = s.substring(1).toInt
        Coord(row, column)
      }


// In file scells/ex5/FormulaParsers.scala

    def range: Parser[Range] = 
      cell~":"~cell ^^ { 
        case c1~":"~c2 => Range(c1, c2) 
      }


// In file scells/ex5/FormulaParsers.scala

  def number: Parser[Number] =
    decimal ^^ (d => Number(d.toDouble))


// In file scells/ex5/FormulaParsers.scala

    def application: Parser[Application] = 
      ident~"("~repsep(expr, ",")~")" ^^ { 
        case f~"("~ps~")" => Application(f, ps) 
      }


// In file scells/ex5/FormulaParsers.scala

    def expr: Parser[Formula] =
      range | cell | number | application


// In file scells/ex5/FormulaParsers.scala

    def textual: Parser[Textual] = 
      """[^=].*""".r ^^ Textual


// In file scells/ex5/FormulaParsers.scala

    def formula: Parser[Formula] = 
      number | textual | "="~>expr


// In file scells/ex5/FormulaParsers.scala

    def parse(input: String): Formula =
      parseAll(formula, input) match {
        case Success(e, _) => e
        case f: NoSuccess => Textual("["+ f.msg +"]")
      }
  } //end FormulaParsers


// In file scells/ex4/Spreadsheet.scala

  package org.stairwaybook.scells
  import swing._
  import event._

  class Spreadsheet(val height: Int, val width: Int) ... {
    val table = new Table(height, width) {
      ...
      reactions += {
        case TableUpdated(table, rows, column) =>
          for (row <- rows)
            cells(row)(column).formula = 
              FormulaParsers.parse(userData(row, column))
      }
    }
  }


// In file scells/ex3/Model.scala

    case class Cell(row: Int, column: Int) {
      var formula: Formula = Empty
      override def toString = formula.toString
    }


  TableUpdated(table, rows, column)


  

35.5 Evaluation

// In file scells/ex5/Evaluator.scala

  package org.stairwaybook.scells
  trait Evaluator { this: Model => ...


// In file scells/ex5/Evaluator.scala

    def evaluate(e: Formula): Double = try {
      e match {
        case Coord(row, column) => 
          cells(row)(column).value
        case Number(v) => 
          v
        case Textual(_) => 
          0
        case Application(function, arguments) =>
          val argvals = arguments flatMap evalList
          operations(function)(argvals)
      }
    } catch {
      case ex: Exception => Double.NaN
    }


// In file scells/ex5/Evaluator.scala

    type Op = List[Double] => Double
    val operations = new collection.mutable.HashMap[String, Op]


// In file scells/ex5/Evaluator.scala

    private def evalList(e: Formula): List[Double] = e match {
      case Range(_, _) => references(e) map (_.value)
      case _ => List(evaluate(e))
    }


// In file scells/ex5/Evaluator.scala

    def references(e: Formula): List[Cell] = e match {
      case Coord(row, column) => 
        List(cells(row)(column))
      case Range(Coord(r1, c1), Coord(r2, c2)) =>
        for (row <- (r1 to r2).toList; column <- c1 to c2)
        yield cells(row)(column)
      case Application(function, arguments) =>
        arguments flatMap references
      case _ =>
        List()
    }
  } // end Evaluator


  

35.6 Operation libraries

// In file scells/ex5/Arithmetic.scala

  package org.stairwaybook.scells
  trait Arithmetic { this: Evaluator =>
    operations += (
      "add"  -> { case List(x, y) => x + y },
      "sub"  -> { case List(x, y) => x - y },
      "div"  -> { case List(x, y) => x / y },
      "mul"  -> { case List(x, y) => x * y },
      "mod"  -> { case List(x, y) => x % y },
      "sum"  -> { xs => (0.0 /: xs)(_ + _) },
      "prod" -> { xs => (1.0 /: xs)(_ * _) }
    )
  }


  { case List(x, y) => x + y }


// In file scells/ex4/Model.scala

  package org.stairwaybook.scells

  class Model(val height: Int, val width: Int) 
      extends Evaluator with Arithmetic { 

    case class Cell(row: Int, column: Int) {
      var formula: Formula = Empty
      def value = evaluate(formula)

      override def toString = formula match {
        case Textual(s) => s
        case _ => value.toString
      }
    }
    
    ... // rest as before
  }


  

35.7 Change propagation

// In file scells/ex5/Model.scala

  package org.stairwaybook.scells
  import swing._

  class Model(val height: Int, val width: Int) 
  extends Evaluator with Arithmetic { 


// In file scells/ex5/Model.scala

    case class Cell(row: Int, column: Int) extends Publisher {
      override def toString = formula match {
        case Textual(s) => s
        case _ => value.toString
      }


// In file scells/ex5/Model.scala

      private var v: Double = 0
      def value: Double = v
      def value_=(w: Double) {
        if (!(v == w || v.isNaN && w.isNaN)) {
          v = w
          publish(ValueChanged(this))
        }
      }


// In file scells/ex5/Model.scala

      private var f: Formula = Empty
      def formula: Formula = f
      def formula_=(f: Formula) {
        for (c <- references(formula)) deafTo(c)
        this.f = f
        for (c <- references(formula)) listenTo(c)
        value = evaluate(f)
      }


// In file scells/ex5/Model.scala

      reactions += {
        case ValueChanged(_) => value = evaluate(formula)
      }
    } // end class Cell


// In file scells/ex5/Model.scala

    case class ValueChanged(cell: Cell) extends event.Event


// In file scells/ex5/Model.scala

    val cells = new Array[Array[Cell]](height, width) 

    for (i <- 0 until height; j <- 0 until width)
      cells(i)(j) = new Cell(i, j)
  } // end class Model


// In file scells/ex5/Spreadsheet.scala

  package org.stairwaybook.scells
  import swing._, event._

  class Spreadsheet(val height: Int, val width: Int) 
      extends ScrollPane {

    val cellModel = new Model(height, width)
    import cellModel._

    val table = new Table(height, width) {
      ... // settings as in Listing X

      override def rendererComponent(
           isSelected: Boolean, hasFocus: Boolean, 
           row: Int, column: Int) =
        ... // as in Listing X

      def userData(row: Int, column: Int): String = 
        ... // as in Listing X

      reactions += {
        case TableUpdated(table, rows, column) =>
          for (row <- rows)
            cells(row)(column).formula = 
              FormulaParsers.parse(userData(row, column))
        case ValueChanged(cell) =>
          updateCell(cell.row, cell.column)
      }

      for (row <- cells; cell <- row) listenTo(cell)
    }

    val rowHeader = new ListView(0 until height) {
      fixedCellWidth = 30
      fixedCellHeight = table.rowHeight
    }

    viewportView = table
    rowHeaderView = rowHeader
  }


  

35.8 Conclusion