Fix reverse and add slice

Author: odersky

tests/run/lst/Lst.scala

@@ -209,7 +209,7 @@ class Lst[+T <: AnyRef](val elems: AnyRef) extends AnyVal {
       val newElems = new Array[AnyRef](elems.length)
       var i = 0
       while (i < elems.length) {
-        newElems(elems.length - i) = elem(i)
+        newElems(elems.length - 1 - i) = elem(i)
         i += 1
       }
       new Lst(newElems)
@@ -229,23 +229,17 @@ class Lst[+T <: AnyRef](val elems: AnyRef) extends AnyVal {
 
   def headOr[U >: T](alt: => U): U = if (length == 0) alt else head
 
-  def drop(n: Int): Lst[T] =
-    if (n <= 0) this
+  def slice(start: Int, end: Int): Lst[T] =
+    if (start < 0) slice(0, end)
     else elems match {
       case null => this
-      case elems: Array[AnyRef] => _fromArray(elems, n, elems.length)
-      case elem: T @ unchecked => Empty
+      case elems: Array[AnyRef] => _fromArray(elems, start, end `min` elems.length)
+      case elem: T @ unchecked => if (end == 0) Empty else this
     }
 
+  def drop(n: Int): Lst[T] = slice(n, length)
   def tail = drop(1)
-
-  def take(n: Int): Lst[T] =
-    if (n <= 0) Empty
-    else elems match {
-      case null => this
-      case elems: Array[AnyRef] => _fromArray(elems, 0, n min elems.length)
-      case elem: T @ unchecked => this
-    }
+  def take(n: Int): Lst[T] = slice(0, n)
 
   def ++ [U >: T <: AnyRef](that: Lst[U]): Lst[U] =
     if (elems == null) that

tests/run/lst/LstTest.scala

@@ -103,7 +103,7 @@ object Test extends App {
     assert(!xs10.contains("f"))
   }
 
-  def foldLeftTest() = {
+  def foldTest() = {
     assert(xs0.foldLeft("x")(_ ++ _) == "x")
     assert(xs1.foldLeft("x")(_ ++ _) == "xa")
     assert(xs2.foldLeft("x")(_ ++ _) == "xab")
@@ -112,6 +112,31 @@ object Test extends App {
     assert(("x" /: xs1)(_ ++ _) == "xa")
     assert(("x" /: xs2)(_ ++ _) == "xab")
     assert(("x" /: xs3)(_ ++ _) == "xabc")
+    assert(xs1.reduceLeft(_ + _) == "a")
+    assert(xs3.reduceLeft(_ + _) == "abc")
+  }
+
+  def reverseTest() = {
+    assert(xs0.reverse === xs0)
+    assert(xs1.reverse === xs1)
+    assert(xs3.reverse.mkString == "c, b, a", xs3.reverse.mkString)
+    assert(xs4.reverse.reverse === xs4, xs4.reverse.reverse)
+  }
+
+  def applyTest() = {
+    assert(xs5.head == "a")
+    assert(xs5.last == "e")
+    assert(xs5(3) == "d")
+    assert(xs1(0) == "a")
+  }
+
+  def sliceTest() = {
+    assert(xs5.slice(2, 4) === Lst("c", "d"))
+    assert(xs5.drop(4) === Lst("e"))
+    assert(xs5.take(4).mkString("") == "abcd")
+    assert(xs5.drop(-1).elems `eq` xs5.elems)
+    assert(xs1.take(1).elems `eq` xs1.elems)
+    assert(xs0.take(10).length == 0)
   }
 
   println("testing")
@@ -125,5 +150,8 @@ object Test extends App {
   existsTest()
   forallTest()
   containsTest()
-  foldLeftTest()
+  foldTest()
+  reverseTest()
+  applyTest()
+  sliceTest()
 }