Sample run of chapter's interpreter examples
// In file working-with-lists/Misc.scala val fruit = List("apples", "oranges", "pears") val nums = List(1, 2, 3, 4) val diag3 = List( List(1, 0, 0), List(0, 1, 0), List(0, 0, 1) ) val empty = List()
// In file working-with-lists/Misc.scala val fruit: List[String] = List("apples", "oranges", "pears") val nums: List[Int] = List(1, 2, 3, 4) val diag3: List[List[Int]] = List( List(1, 0, 0), List(0, 1, 0), List(0, 0, 1) ) val empty: List[Nothing] = List()
// In file working-with-lists/Misc.scala // List[Nothing] is also of type List[String]! val xs: List[String] = List()
// In file working-with-lists/Misc.scala val fruit = "apples" :: ("oranges" :: ("pears" :: Nil)) val nums = 1 :: (2 :: (3 :: (4 :: Nil))) val diag3 = (1 :: (0 :: (0 :: Nil))) :: (0 :: (1 :: (0 :: Nil))) :: (0 :: (0 :: (1 :: Nil))) :: Nil val empty = Nil
// In file working-with-lists/Misc.scala val nums = 1 :: 2 :: 3 :: 4 :: Nil
scala> Nil.head java.util.NoSuchElementException: head of empty list
// In file working-with-lists/InsertionSort1.scala def isort(xs: List[Int]): List[Int] = if xs.isEmpty then Nil else insert(xs.head, isort(xs.tail)) def insert(x: Int, xs: List[Int]): List[Int] = if xs.isEmpty || x <= xs.head then x :: xs else xs.head :: insert(x, xs.tail)
scala> val List(a, b, c) = fruit val a: String = apples val b: String = oranges val c: String = pears
scala> val a :: b :: rest = fruit val a: String = apples val b: String = oranges val rest: List[String] = List(pears)
// In file working-with-lists/InsertionSort2.scala def isort(xs: List[Int]): List[Int] = xs match case List() => List() case x :: xs1 => insert(x, isort(xs1)) def insert(x: Int, xs: List[Int]): List[Int] = xs match case List() => List(x) case y :: ys => if x <= y then x :: xs else y :: insert(x, ys)
List(1, 2) ::: List(3, 4, 5) // List(1, 2, 3, 4, 5) List() ::: List(1, 2, 3) // List(1, 2, 3) List(1, 2, 3) ::: List(4) // List(1, 2, 3, 4)
// In file working-with-lists/Misc.scala xs ::: ys ::: zs
// In file working-with-lists/Misc.scala xs ::: (ys ::: zs)
def append[T](xs: List[T], ys: List[T]): List[T]
def append[T](xs: List[T], ys: List[T]): List[T] = xs match case List() => ??? case x :: xs1 => ???
case List() => ys
// In file working-with-lists/Misc.scala def append[T](xs: List[T], ys: List[T]): List[T] = xs match case List() => ys case x :: xs1 => x :: append(xs1, ys)
List(1, 2, 3).length // 3
val abcde = List('a', 'b', 'c', 'd', 'e') abcde.last // e abcde.init // List(a, b, c, d)
scala> List().init java.lang.UnsupportedOperationException: init of empty list at ... scala> List().last java.util.NoSuchElementException: last of empty list at ...
abcde.reverse // List(e, d, c, b, a)
abcde // List(a, b, c, d, e)
xs.reverse.reverse equals xs
xs.reverse.init equals xs.tail.reverse xs.reverse.tail equals xs.init.reverse xs.reverse.head equals xs.last xs.reverse.last equals xs.head
// In file working-with-lists/Reverse1.scala def rev[T](xs: List[T]): List[T] = xs match case List() => xs case x :: xs1 => rev(xs1) ::: List(x)
abcde.take(2) // List(a, b) abcde.drop(2) // List(c, d, e) abcde.splitAt(2) // (List(a, b),List(c, d, e))
abcde.apply(2) // c (rare in Scala)
abcde(2) // c (rare in Scala)
abcde.indices // Range 0 until 5
List(List(1, 2), List(3), List(), List(4, 5)).flatten // List(1, 2, 3, 4, 5) fruit.map(_.toList).flatten // List(a, p, p, l, e, s, o, r, a, n, g, e, // s, p, e, a, r, s)
scala> List(1, 2, 3).flatten 1 |List(1, 2, 3).flatten | ^ | No implicit view available from | Int => IterableOnce[B] | where, B is a type variable.
abcde.indices.zip(abcde) // Vector((0,a), (1,b), (2,c), (3,d), (4,e))
val zipped = abcde.zip(List(1, 2, 3)) // List((a,1), (b,2), (c,3))
abcde.zipWithIndex // List((a,0), (b,1), (c,2), (d,3), (e,4))
zipped.unzip // (List(a, b, c),List(1, 2, 3))
abcde.toString // List(a, b, c, d, e)
abcde.mkString("[", ",", "]") // [a,b,c,d,e] abcde.mkString("") // abcde abcde.mkString // abcde abcde.mkString("List(", ", ", ")") // List(a, b, c, d, e)
val buf = new StringBuilder abcde.addString(buf, "(", ";", ")") // (a;b;c;d;e)
val arr = abcde.toArray // Array(a, b, c, d, e) arr.toList // List(a, b, c, d, e)
xs.copyToArray(arr, start)
val arr2 = new Array[Int](10) // Array(0, 0, 0, 0, 0, 0, 0, 0, 0, 0) List(1, 2, 3).copyToArray(arr2, 3) arr2 // Array(0, 0, 0, 1, 2, 3, 0, 0, 0, 0)
val it = abcde.iterator it.next() // a it.next() // b
// In file working-with-lists/Misc.scala def msort[T](less: (T, T) => Boolean) (xs: List[T]): List[T] = def merge(xs: List[T], ys: List[T]): List[T] = (xs, ys) match case (Nil, _) => ys case (_, Nil) => xs case (x :: xs1, y :: ys1) => if less(x, y) then x :: merge(xs1, ys) else y :: merge(xs, ys1) val n = xs.length / 2 if n == 0 then xs else val (ys, zs) = xs.splitAt(n) merge(msort(less)(ys), msort(less)(zs))
msort((x: Int, y: Int) => x < y)(List(5, 7, 1, 3)) // List(1, 3, 5, 7)
val intSort = msort((x: Int, y: Int) => x < y) // intSort has type List[Int] => List[Int]
val reverseIntSort = msort((x: Int, y: Int) => x > y)
val mixedInts = List(4, 1, 9, 0, 5, 8, 3, 6, 2, 7) intSort(mixedInts) // List(0, 1, 2, 3, 4, 5, 6, 7, 8, 9) reverseIntSort(mixedInts) // List(9, 8, 7, 6, 5, 4, 3, 2, 1, 0)
List(1, 2, 3).map(_ + 1) // List(2, 3, 4) val words = List("the", "quick", "brown", "fox") words.map(_.length) // List(3, 5, 5, 3) words.map(_.toList.reverse.mkString) // List(eht, kciuq, nworb, xof)
words.map(_.toList) // List(List(t, h, e), List(q, u, i, c, k), // List(b, r, o, w, n), List(f, o, x)) words.flatMap(_.toList) // List(t, h, e, q, u, i, c, k, b, r, o, w, n, f, o, x)
List.range(1, 5).flatMap( i => List.range(1, i).map(j => (i, j)) ) // List((2,1), (3,1), (3,2), (4,1), // (4,2), (4,3))
// In file working-with-lists/Misc.scala for i <- List.range(1, 5); j <- List.range(1, i) yield (i, j)
scala> var sum = 0 var sum: Int = 0 scala> List(1, 2, 3, 4, 5).foreach(sum += _) scala> sum val res39: Int = 15
List(1, 2, 3, 4, 5).filter(_ % 2 == 0) // List(2, 4) words.filter(_.length == 3) // List(the, fox)
List(1, 2, 3, 4, 5).partition(_ % 2 == 0) // (List(2, 4),List(1, 3, 5))
List(1, 2, 3, 4, 5).find(_ % 2 == 0) // Some(2) List(1, 2, 3, 4, 5).find(_ <= 0) // None
List(1, 2, 3, -4, 5).takeWhile(_ > 0) // List(1, 2, 3) words.dropWhile(_.startsWith("t")) // List(quick, brown, fox)
List(1, 2, 3, -4, 5).span(_ > 0) // (List(1, 2, 3),List(-4, 5))
def hasZeroRow(m: List[List[Int]]) = m.exists(row => row.forall(_ == 0)) hasZeroRow(diag3) // false
def sum(xs: List[Int]): Int = xs.foldLeft(0)(_ + _)
def product(xs: List[Int]): Int = xs.foldLeft(1)(_ * _)
words.foldLeft("")(_ + " " + _) // " the quick brown fox"
words.tail.foldLeft(words.head)(_ + " " + _) // "the quick brown fox"
def flattenLeft[T](xss: List[List[T]]) = xss.foldLeft(List[T]())(_ ::: _) def flattenRight[T](xss: List[List[T]]) = xss.foldRight(List[T]())(_ ::: _)
scala> def flattenRight[T](xss: List[List[T]]) = | xss.foldRight(List())(_ ::: _) 2 | xss.foldRight(List())(_ ::: _) | ^ | Found: (_$1 : List[T]) | Required: List[Nothing]
def reverseLeft[T](xs: List[T]) = xs.foldLeft(\startValue)(\operation)
// In file working-with-lists/Reverse2.scala def reverseLeft[T](xs: List[T]) = xs.foldLeft(List[T]()) { (ys, y) => y :: ys }
List(1, -3, 4, 2, 6).sortWith(_ < _) // List(-3, 1, 2, 4, 6) words.sortWith(_.length > _.length) // List(quick, brown, the, fox)
List.apply(1, 2, 3) // List(1, 2, 3)
List.range(1, 5) // List(1, 2, 3, 4) List.range(1, 9, 2) // List(1, 3, 5, 7) List.range(9, 1, -3) // List(9, 6, 3)
List.fill(5)('a') // List(a, a, a, a, a) List.fill(3)("hello") // List(hello, hello, hello)
List.fill(2, 3)('b') // List(List(b, b, b), List(b, b, b))
val squares = List.tabulate(5)(n => n * n) // List(0, 1, 4, 9, 16) val multiplication = List.tabulate(5,5)(_ * _) // List(List(0, 0, 0, 0, 0), // List(0, 1, 2, 3, 4), List(0, 2, 4, 6, 8), // List(0, 3, 6, 9, 12), List(0, 4, 8, 12, 16))
List.concat(List('a', 'b'), List('c')) // List(a, b, c) List.concat(List(), List('b'), List('c')) // List(b, c) List.concat() // List()
(List(10, 20).zip(List(3, 4, 5))).map { (x, y) => x * y } // List(30, 80)
(List(10, 20).lazyZip(List(3, 4, 5))).map(_ * _) // List(30, 80)
(List("abc", "de").lazyZip(List(3, 2))).forall(_.length == _) // true (List("abc", "de").lazyZip(List(3, 2))).exists(_.length != _) // false
msort((x: Char, y: Char) => x > y)(abcde) // List(e, d, c, b, a)
abcde.sortWith(_ > _) // List(e, d, c, b, a)
scala> msort(_ > _)(abcde) 1 |msort(_ > _)(abcde) | ^^^ |value > is not a member of Any, but could be made | available as an extension method.
msort[Char](_ > _)(abcde) // List(e, d, c, b, a)
def msortSwapped[T](xs: List[T])(less: (T, T) => Boolean): List[T] = ... // same implementation as msort, // but with arguments swapped
msortSwapped(abcde)(_ > _) // List(e, d, c, b, a)
xss.foldRight(List[T]())(_ ::: _)
xs.foldRight(z)(op)
xss.foldRight(List())(_ ::: _) // this won't compile
(List[T], List[Nothing]) => List[Nothing]
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