A post on Scala pattern matching

I am looking for some advice from the older kids again ;-)

Last time I was playing with a grid and the game continues.  I want to add words to the grid but find that this is full of type mismatches, which I have commented in the code below.

This experience dims the Scala lustre a little for me since I don't want to have all of this 'casting' and type manipulation in the code.  And I imagine that it is not needed .... or should I say that I hope it is not needed and so I am looking to you experts for some more tips and tricks.

Here is the code along with my queries / complaints....

// Add words to a grid in the horizontal plane
class Horizontal (grid: Array[Array[String]]) extends Direction {

    override def addWord(word: String) = {

        val possibleStartingPoints = for(row <- 0 until grid.length; column <- 0 until (grid(0).length - word.length)) yield new Coordinate(row, column)

        val allowableStartingPoints = possibleStartingPoints.filter(checkWordAllowable(word, _))

        addWordHorizontal(word, allowableStartingPoints(new Random().nextInt(allowableStartingPoints.length)))
    }

    // Can safely assume that the word will fit ... but will the letters of this word clash with another?
    private def checkWordAllowable(word: String, coordinate: Coordinate) : Boolean = {

        val gridLetters = for (letter <- coordinate.y until (coordinate.y + word.length)) yield grid(coordinate.x)(letter)

        val wordAsLetterList = getWordAsList(word)

//        val wordLettersGridLettersPairs = wordAsLetterList zip gridLetters // Would be nice but...
//              found   : RandomAccessSeq.Projection[String]
//              required: List[?]

        val wordLettersGridLettersPairs = wordAsLetterList zip gridLetters.toList // toList casting :(

        val allowableSpaceList = for (pair <- wordLettersGridLettersPairs) yield (pair._2 == null || pair._1 == pair._2)

        wordAsLetterList.length == allowableSpaceList.length
    }

    private def getWordAsList(word: String) : List[String] = {
//        for (letter <- 0 until word.length) yield word.substring(letter, letter+1)    // Would be nicer methinks but...
// Compiler complains:          found   : RandomAccessSeq.Projection[java.lang.String]
//                              required: List[String]
        val wordAsList = for (letter <- 0 until word.length) yield word.substring(letter, letter+1)
        wordAsList.toList
    }

    // A little clunky, but this works
    private def addWordHorizontal(word: String, coordinate: Coordinate) = {
        var gridCoordinate = coordinate
        for (letter <- getWordAsList(word)) {
            grid(gridCoordinate.x)(gridCoordinate.y) = letter
            gridCoordinate = new Coordinate(coordinate.x, gridCoordinate.y + 1)
        }
    }
}

// Abstract class ... no complaints here - I will use this as a base for horizontal, diagonal and vertical
abstract class Direction {

    def addWord(word: String)
 
}

Any help or advice would be greatly appreciated

Ray

(for (foo <- foos) yield new Bar(foo.name)).toList

The toList should fix your two issues. I'm surprised zip needs a List
and not a Seq.

2009/9/21 :
>
> I am looking for some advice from the older kids again ;-)
>
> Last time I was playing with a grid and the game continues.  I want to add
> words to the grid but find that this is full of type mismatches, which I
> have commented in the code below.
>
> This experience dims the Scala lustre a little for me since I don't want to
> have all of this 'casting' and type manipulation in the code.  And I imagine
> that it is not needed .... or should I say that I hope it is not needed and
> so I am looking to you experts for some more tips and tricks.
>
> Here is the code along with my queries / complaints....
>
> // Add words to a grid in the horizontal plane
> class Horizontal (grid: Array[Array[String]]) extends Direction {
>
>     override def addWord(word: String) = {
>
>         val possibleStartingPoints = for(row <- 0 until grid.length; column
> <- 0 until (grid(0).length - word.length)) yield new Coordinate(row, column)
>
>         val allowableStartingPoints =
> possibleStartingPoints.filter(checkWordAllowable(word, _))
>
>         addWordHorizontal(word, allowableStartingPoints(new
> Random().nextInt(allowableStartingPoints.length)))
>     }
>
>     // Can safely assume that the word will fit ... but will the letters of
> this word clash with another?
>     private def checkWordAllowable(word: String, coordinate: Coordinate) :
> Boolean = {
>
>         val gridLetters = for (letter <- coordinate.y until (coordinate.y +
> word.length)) yield grid(coordinate.x)(letter)
>
>         val wordAsLetterList = getWordAsList(word)
>
> //        val wordLettersGridLettersPairs = wordAsLetterList zip gridLetters
> // Would be nice but...
> //              found   : RandomAccessSeq.Projection[String]
> //              required: List[?]
>
>         val wordLettersGridLettersPairs = wordAsLetterList zip
> gridLetters.toList // toList casting :(
>
>         val allowableSpaceList = for (pair <- wordLettersGridLettersPairs)
> yield (pair._2 == null || pair._1 == pair._2)
>
>         wordAsLetterList.length == allowableSpaceList.length
>     }
>
>     private def getWordAsList(word: String) : List[String] = {
> //        for (letter <- 0 until word.length) yield word.substring(letter,
> letter+1)    // Would be nicer methinks but...
> // Compiler complains:          found   :
> RandomAccessSeq.Projection[java.lang.String]
> //                              required: List[String]
>         val wordAsList = for (letter <- 0 until word.length) yield
> word.substring(letter, letter+1)
>         wordAsList.toList
>     }
>
>     // A little clunky, but this works
>     private def addWordHorizontal(word: String, coordinate: Coordinate) = {
>         var gridCoordinate = coordinate
>         for (letter <- getWordAsList(word)) {
>             grid(gridCoordinate.x)(gridCoordinate.y) = letter
>             gridCoordinate = new Coordinate(coordinate.x, gridCoordinate.y +
> 1)
>         }
>     }
> }
>
> // Abstract class ... no complaints here - I will use this as a base for
> horizontal, diagonal and vertical
> abstract class Direction {
>
>     def addWord(word: String)
>
> }
>
> Any help or advice would be greatly appreciated
>
> Ray