scalaz.example.ExampleFold.scala Maven / Gradle / Ivy

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package scalaz.example

import scalaz._

object ExampleFold {
  def main(args: Array[String]) = run

  import Scalaz._

  def run {
    // Folding left over a List
    (List(1, 2, 3).foldl("0")((a, b) => "f(" + a.toString + ", " + b + ")")) assert_=== "f(f(f(0, 1), 2), 3)"

    // Folding right over a List    
    (List(1, 2, 3).foldr("0")((a, b) => "f(" + a.toString + ", " + b + ")")) assert_=== "f(1, f(2, f(3, 0)))"

    // Folding left over a List
    (List(1, 2, 3).foldl(0)(_ + _)) assert_=== 6

    // Folding left over a List, using the first value as the starting value.
    (List(1, 2, 3) foldl1 (_ + _)) assert_=== some(6)

    // Folding left over an empty List, using the first value as the starting value.
    (List.empty[Int] foldl1 (_ + _)) assert_=== none

    // Summing over a List using Foldable, using the Int Monoid to combine the elements.
    (List(1, 2, 3).asMA.sum) assert_=== 6

    // Summing over a List using Foldable, using the String Monoid to combine the elements.
    (List("a", "b", "c").asMA.sum) assert_=== "abc"

    // Checking for existence of an element that satisfies a predicate.
    ("abC".toList ∃ (c => Character.isUpperCase(c))) assert_=== true

    // Checking for existence of an element that satisfies a predicate, using Stream Foldable,
    // which lazily handles the infinite Stream.
    (Stream.continually(1) ∃ (_ > 0)) assert_=== true

    Set(1, 2, 3) ∃ { _ % 2 == 0 } assert_=== true

    // Checking if all elements satisfy a predicate, using Stream Foldable,
    // which lazily handles the infinite Stream.
    (Stream.continually(1) ∀ (_ == 0)) assert_=== false

    // Counting the elements using Seq Foldable
    ("123".toSeq.asMA.count) assert_=== 3

    // Counting the elements using Option Foldable
    (some(0).asMA.count) assert_=== 1

    (50 ∈: Stream.range(0, 100)) assert_=== true

    Stream.range(0, 100) ∋ 50 assert_=== true

    (1 to 10).toList splitWith {_ % 5 < 2} assert_=== List(List(1), List(2, 3, 4), List(5, 6), List(7, 8, 9), List(10))

    (1 to 10).toList selectSplit {_ % 5 < 2} assert_=== List(List(1), List(5, 6), List(10))
  }
}