Scala : week2: implement forall, exists, map

1 files changed, 12 insertions, 10 deletions

diff --git a/Scala/funsets/src/main/scala/funsets/FunSets.scala b/Scala/funsets/src/main/scala/funsets/FunSets.scala
index 15a6bfc..99b0748 100644
--- a/Scala/funsets/src/main/scala/funsets/FunSets.scala
+++ b/Scala/funsets/src/main/scala/funsets/FunSets.scala
@@ -20,25 +20,25 @@ object FunSets {
   /**
    * Returns the set of the one given element.
    */
-  def singletonSet(elem: Int): Set = (x =>  x == elem)
+  def singletonSet(elem: Int): Set = x =>  x == elem
 
   /**
    * Returns the union of the two given sets,
    * the sets of all elements that are in either `s` or `t`.
    */
-  def union(s: Set, t: Set): Set = (x => s(x) | t(x))
+  def union(s: Set, t: Set): Set = x => s(x) | t(x)
 
   /**
    * Returns the intersection of the two given sets,
    * the set of all elements that are both in `s` and `t`.
    */
-  def intersect(s: Set, t: Set): Set = (x => s(x) & t(x))
+  def intersect(s: Set, t: Set): Set = x => s(x) & t(x)
 
   /**
    * Returns the difference of the two given sets,
    * the set of all elements of `s` that are not in `t`.
    */
-  def diff(s: Set, t: Set): Set = (x => s(x) & !t(x))
+  def diff(s: Set, t: Set): Set = x => s(x) & !t(x)
 
   /**
    * Returns the subset of `s` for which `p` holds.
@@ -56,23 +56,25 @@ object FunSets {
    */
   def forall(s: Set, p: Int => Boolean): Boolean = {
     def iter(a: Int): Boolean = {
-      if (???) ???
-      else if (???) ???
-      else iter(???)
+      if (a > bound) true
+      else if (contains(s, a) && !p(a)) false
+      else iter(a + 1)
     }
-    iter(???)
+    iter(-bound)
   }
 
   /**
    * Returns whether there exists a bounded integer within `s`
    * that satisfies `p`.
    */
-  def exists(s: Set, p: Int => Boolean): Boolean = ???
+   // elements of s do NOT all NOT satisfy p
+   def exists(s: Set, p: Int => Boolean): Boolean = !forall(s, x => !p(x))
 
   /**
    * Returns a set transformed by applying `f` to each element of `s`.
    */
-  def map(s: Set, f: Int => Int): Set = ???
+  // x is in S' if exists y in S so that f(y) = x
+  def map(s: Set, f: Int => Int): Set = x => exists(s, y => f(y) == x)
 
   /**
    * Displays the contents of a set