https://www.coursera.org/learn/progfun1/programming/BVa6a/functional-sets

Assignment: Functional Sets REPL playground

scala> type Set = Int => Boolean
defined type alias Set

scala> Set
res0: scala.collection.immutable.Set.type = scala.collection.immutable.Set$@7a7f0991

scala> def contains(s: Set, elem: Int): Boolean = s(elem)
contains: (s: Int => Boolean, elem: Int)Boolean

scala> contains(x => x%2 == 0, 2)
res1: Boolean = true

scala> contains(x => x%2 == 0, 1)
res2: Boolean = false

scala> contains(x => x>100, 1)
res3: Boolean = false

scala> contains(x => x>100, 2)
res4: Boolean = false

scala> contains(x => x>100, 99)
res5: Boolean = false

scala> contains(x => x>100, 100)
res6: Boolean = false

scala> contains(x => x>100, 101)
res7: Boolean = true

scala> val s1 = singletonSet(1)
<console>:40: error: not found: value singletonSet
       val s1 = singletonSet(1)
                ^

scala> val s1 = Set(1)
s1: scala.collection.immutable.Set[Int] = Set(1)

scala> val s2 = Set(2)
s2: scala.collection.immutable.Set[Int] = Set(2)

scala> union(s1, s2)
<console>:43: error: not found: value union
              union(s1, s2)
              ^

scala> def union(a: Set, b:Set) = a+b
<console>:41: error: type mismatch;
 found   : Int => Boolean
 required: String
       def union(a: Set, b:Set) = a+b
                                    ^

scala> def union(a: Set, b:Set) = a.concat(b)
<console>:41: error: value concat is not a member of Int => Boolean
       def union(a: Set, b:Set) = a.concat(b)
                                    ^

scala> s1 || s2
<console>:43: error: value || is not a member of scala.collection.immutable.Set[Int]
              s1 || s2
                 ^

scala> s1 | s2
res10: scala.collection.immutable.Set[Int] = Set(1, 2)

scala> s1 & s2
res11: scala.collection.immutable.Set[Int] = Set()

scala> s1 | s2
res12: scala.collection.immutable.Set[Int] = Set(1, 2)

scala> Set(1) | Set(2)
res13: scala.collection.immutable.Set[Int] = Set(1, 2)

scala> Set(1) | Set(2)(1)
<console>:41: error: type mismatch;
 found   : Boolean
 required: scala.collection.GenSet[Int]
              Set(1) | Set(2)(1)
                             ^

scala> (Set(1) | Set(2))(1)
res15: Boolean = true

scala> (Set(1) | Set(2))(2)
res16: Boolean = true

scala> (Set(1) | Set(2))(3)
res17: Boolean = false