March 2014 update

Task/Fibonacci-sequence/Scala/fibonacci-sequence-2.scala

@@ -1,9 +1 @@
-//syntactic sugar for Stream.cons, this is unnecessary but makes the definition prettier
-//Stream.cons(head,stream) becomes head::stream
-//I think 2.8 will have #::
-class PrettyStream[A](str: =>Stream[A]) {
-    def ::(hd: A) = Stream.cons(hd, str)
-}
-implicit def streamToPrettyStream[A](str: =>Stream[A]) = new PrettyStream(str)
-
-def fib: Stream[Int] = 0 :: 1 :: fib.zip(fib.tail).map{case (a,b) => a + b}
+lazy val fib: Stream[Int] = 0 #:: 1 #:: fib.zip(fib.tail).map{case (a,b) => a + b}

Task/Fibonacci-sequence/Scala/fibonacci-sequence-3.scala

@@ -1 +1,4 @@
-def fib: Stream[Int] = 0 #:: 1 #:: fib.zip(fib.tail).map{case (a,b) => a + b}
+def fib(i:Int, a:Int=1, b:Int=0):Int = i match{
+    case 1 => b
+    case _ => fib(i-1, b, a+b)
+}

Task/Fibonacci-sequence/Scala/fibonacci-sequence-4.scala

@@ -1,7 +1,13 @@
-def fib(i:Int):Int = {
-    def fib2(i:Int, a:Int, b:Int):Int = i match{
-        case 1 => b
-        case _ => fib2(i-1, b, a+b)
-    }
-    fib2(i,1,0)
+// Fibonacci using BigInt with Stream.foldLeft optimized for GC (Scala v2.9 and above)
+// Does not run out of memory for very large Fibonacci numbers
+def fib(n:Int) = {
+
+  def series(i:BigInt,j:BigInt):Stream[BigInt] = i #:: series(j, i+j)
+
+  series(1,0).take(n).foldLeft(BigInt("0"))(_+_)
 }
+
+// Small test
+(0 to 13) foreach {n => print(fib(n).toString + " ")}
+
+// result: 0 1 1 2 3 5 8 13 21 34 55 89 144 233