Scala Bowling Kata - still in the middle I suppose 79
I had a 3.5 hour flight today. I realized I was missing some of the validation from the Ruby version related to how many rolls a valid game should allow:
I had a mini state machine to track whether the first ball had been thrown yet or not. I replaced that by walking the list of scores:
"One more roll on a game with 20 rolls and an open 10th frame" should {
20 times { roll(1) }
roll(1) must throwA[IllegalArgumentException]
}
"Two more rolls a game with 10 spares" should {
10 times { spare }
roll(1)
roll(1) must throwA[IllegalArgumentException]
}
"Two marks in the 10th frame should" should {
18 times { roll(1) }
strike
spare
roll(1) must throwA[IllegalArgumentException]
}On my flight from DFW to SNA, I got these behaviors implemented. The code was pretty ugly!
However, ugly code in hand, passing examples, a slight understanding of some of the problems with my code and a desire to make the BowlingScorer immutable was all I needed to make progress.
I removed the index instance field by rewriting the score method and injecting a tuple into foldLeft (written here using the short-hand notation /:): def scoreAt(frame:Int) =
((0,0) /: (1 to frame)) { (t, _) =>
(t._1 + scoreAtIndex(t._2), t._2 + incrementAt(t._2))
}._1 def onFirstThrow = {
var index = 0
while(index < rolls.length)
if(isStrike(index)) index += 1 else index += 2
index == rolls.length
}While I am happy I was able to remove the index variable, which was really a parameter being passed around in a field (ugly), I am not happy with this method.
I changed the roll method to return a new instance of a BowlingScorer, making the bowling scorer immutable: def roll(roll:Int) = {
validate(roll)
new BowlingScorer(rolls ++ Array(roll))
}So I think I’m still somewhere in the middle of working through this code. Again, I’m still learning Scala. I have a lot to learn. I really only barely understand functional programming and, frankly, the Eclipse IDE, while functional, is getting in the way quite a bit. So for a toy example it is OK. Given the choice of this environment or vi and the command line, I’d not pick the former. (I might give the other IDE’s a go, but that’s not really what I’m interested in learning right now.)
So here’s the next version. I plan to work through all of the comments I’ve yet to process from the previous blog posting over the next few days. If you can recommend a better implementation of onFirstThrow, I’d appreciate it.
Other general comments also welcome.
BowlingScorerExampleGroup.scala
package com.om.example
import org.specs._
object BowlingScorerExampleGroup extends SpecificationWithJUnit {
var scorer = new BowlingScorer(Nil);
def roll(value:Int) =
scorer = scorer.roll(value)
def haveAScoreOf(expected:Int) =
scorer.score must_== expected
def strike =
roll(10)
def spare {
roll(5)
roll(5)
}
implicit def intToDo(count: Int) = {
new {
def times(f: => Unit) = {
1 to count foreach { _ => f }
}
}
}
"A Newly Created Bowling Scorer" should {
haveAScoreOf(0)
}
"A game with all 0's" should {
20 times { roll(0) }
haveAScoreOf(0)
}
"A game with all 1's" should {
20 times { roll(1) }
haveAScoreOf(20)
}
"A game with a single spare followed by a 5" should {
spare
roll(5)
haveAScoreOf(20)
}
"A game with all 5's" should {
10 times { spare }
roll(5)
haveAScoreOf(150)
}
"A game with a single strike followed by a 4" should {
strike
roll(4)
haveAScoreOf(18)
}
"A game with a strike, spare then an open frame with two 3's" should {
strike
spare
2 times { roll(3) }
haveAScoreOf(39)
}
"A game with strike, spare then an open frame with two 3's" should {
spare
strike
2 times { roll(3) }
haveAScoreOf(42)
}
"A Dutch 200 game, Spare-Strike" should {
5 times {
spare
strike
}
spare
haveAScoreOf(200)
}
"A Dutch 200 game, Strike-Spare" should {
5 times {
strike
spare
}
strike
haveAScoreOf(200)
}
"A Perfect game" should {
12 times { strike }
haveAScoreOf(300)
}
"The score for each frame of a Perfect game, each frame" should {
12 times { strike }
1 to 10 foreach { frame => scorer.scoreAt(frame) must_== 30 * frame }
}
"An individaul roll of > 10" should {
roll(11) must throwA[IllegalArgumentException]
}
"An iniviaul roll of < 0" should {
roll(-1) must throwA[IllegalArgumentException]
}
"A frame trying to contain more than 10 pins" should {
roll(8)
roll(3) must throwA[IllegalArgumentException]
}
"One more roll on a game with 20 rolls and an open 10th frame" should {
20 times { roll(1) }
roll(1) must throwA[IllegalArgumentException]
}
"Two more rolls a game with 10 spares" should {
10 times { spare }
roll(1)
roll(1) must throwA[IllegalArgumentException]
}
"Two marks in the 10th frame should" should {
18 times { roll(1) }
strike
spare
roll(1) must throwA[IllegalArgumentException]
}
}BowlingScorer.scala
package com.om.example
class BowlingScorer(rollsSoFar:List[Int]){
val rolls:List[Int] = rollsSoFar
def roll(roll:Int) = {
validate(roll)
new BowlingScorer(rolls ++ Array(roll))
}
def validate(roll:Int) {
if(invalidRoll(roll))
throw new IllegalArgumentException("Individaul rolls must be from 0 .. 10")
if(frameRollTooHigh(roll))
throw new IllegalArgumentException("Total of rolls for frame must not exceed 10");
if(willBeTooManyRolls)
throw new IllegalArgumentException("Game over, no more rolls allowed")
}
def invalidRoll(roll:Int) =
(0 to 10 contains(roll)) == false
def frameRollTooHigh(roll:Int) =
openScoreAt(indexToValidate) + roll > 10
def willBeTooManyRolls =
tenthRolled(indexOf10thFrame) && nextRollTooMany(indexOf10thFrame)
def tenthRolled(tenthIndex:Int) =
tenthIndex < rolls.length
def nextRollTooMany(tenthIndex: Int) =
allowedTenthFrameRolls(tenthIndex) < rollsInTenthFrame(tenthIndex) + 1
def indexOf10thFrame =
(0 /: (1 until 10)) {(c, _) => c + incrementAt(c)}
def allowedTenthFrameRolls(index:Int) =
if(isMark(index)) 3 else 2
def rollsInTenthFrame(index: Int) =
rolls.length - index
def indexToValidate =
if(onFirstThrow) rolls.length else rolls.length - 1
def onFirstThrow = {
var index = 0
while(index < rolls.length)
if(isStrike(index)) index += 1 else index += 2
index == rolls.length
}
def scoreAt(frame:Int) =
((0,0) /: (1 to frame)) { (t, _) =>
(t._1 + scoreAtIndex(t._2), t._2 + incrementAt(t._2))
}._1
def score = scoreAt(10)
def scoreAtIndex(index:Int) =
if(isMark(index)) markScoreAt(index) else openScoreAt(index)
def incrementAt(index:Int) =
if(isStrike(index)) 1 else 2
def isMark(index:Int) =
isStrike(index) || isSpare(index)
def isStrike(index:Int) =
valueAt(index) == 10
def markScoreAt(index:Int) =
sumNext(index, 3)
def isSpare(index:Int) =
openScoreAt(index) == 10 && valueAt(index) != 10
def openScoreAt(index:Int) =
sumNext(index, 2)
def sumNext(index:Int, count:Int) =
(0 /: (index until index+count))(_ + valueAt(_))
def valueAt(index:Int) =
if(rolls.length > index) rolls(index) else 0
}
While I am happy I was able to remove the index variable, which was really a parameter being passed around in a field (ugly), I am not happy with this method.
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I changed the roll method to return a new instance of a BowlingScorer, making the bowling scorer immutable
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