pep-material: comparison progs/lecture1.scala

equal deleted inserted replaced

-:cd2a9c969ef2
+:b8e3f32d6097
 lst(0)
 lst(2)
 // some alterative syntax for lists
-1::2::3::Nil
+1 :: 2 :: 3 :: Nil
 List(1, 2, 3) ::: List(4, 5, 6)
 // Printing/Strings
 //==================
 /* in Java
 val lyrics = "Sun dips down, the day has gone. \n" +
 "Witches, wolves and giants yawn. \n" +
 "Queen and dragon, troll and gnome: \n" +
-"tired buddies head for home"
+"tired buddies head for home."
 */
 val lyrics = """Sun dips down, the day has gone.
 |Witches, wolves and giants yawn.
 |Queen and dragon, troll and gnome:
-|tired buddies head for home""".stripMargin
+|tired buddies head for home.""".stripMargin
 println(lyrics)
 // Pairs/Tuples
 // If-Conditionals
 //=================
+// Scala does not have a then-keyword
+// both if-else branches need to be presents
 def fact(n: Int) : Int =
 if (n == 0) 1 else n * fact(n - 1)
 !      not
 && ||  and, or
 */
-def fact2(n: BigInt): BigInt =
+def fact2(n: BigInt) : BigInt =
 if (n == 0) 1 else n * fact2(n - 1)
 fact2(150)
-def fib(n: Int): Int =
+def fib(n: Int) : Int =
 if (n == 0) 1 else
 if (n == 1) 1 else fib(n - 1) + fib(n - 2)
 //gcd - Euclid's algorithm
 for (n <- (1 to 10).toList;
 m <- (1 to 10).toList) yield m * n
 mult_table.sliding(10,10).mkString("\n")
+// the list can also be constructed in any other way
+for (n <- List(10,12,4,5,7,8,10)) yield n * n
 // with if-predicates
 for (n <- (1 to 3).toList;
 m <- (1 to 3).toList;
 for ((m, n) <- List((1, 4), (2, 3), (3, 2), (4, 1))) yield m + n
 for (p <- List((1, 4), (2, 3), (3, 2), (4, 1))) yield p._1 + p._2
+// general pattern
+for (x <- ...) yield {
+// potentially complicated
+// calculation of a result
+}
 // with only a side-effect (no list is produced),
 // has no "yield"
 for (n <- (1 to 10)) println(n)
 // concurrency (ONLY WORKS IN SCALA 2.11.8, not in SCALA 2.12)
 //             (would need to have this wrapped into a function, or
 time_needed(10, for (n <- list) yield n + 42)
 time_needed(10, for (n <- list.par) yield n + 42)
 // mutable vs immutable factorial
-def fact_mu(n: Long): Long = {
+def fact_mu(n: Long) : Long = {
 var result : Long = 1
 var i = 1
 while (i <= n) {
 result = result * i
 i = i + 1
 val l2 = for (n <- (List.fill(100000)(20 to 21)).flatten.par) yield fact_im(n)
 l1.sum - l2.sum
 }
 }
-test().sum
+(for (i <- (1 to 10)) yield test().sum).sum
-println(l1.sum - l2.sum)
 // Webpages
 //==========
 import io.Source
 plan.par.map(i(_)).reduce(_ + _)
 santa_state("(((((()))))".toList)
 santa_imutable("(((((()))))".toList)
-def randomString(length: Int) =
+def randomString(length: Int) : String =
 List.fill(length)((40 + scala.util.Random.nextInt(2)).toChar)
 santa_state(randomString(100))

changeset 193	b8e3f32d6097
parent 189	5777744fe354
child 195	4bacbe753e66