pep-material: comparison progs/lecture1.scala

equal deleted inserted replaced

-:b28e976dcd65
+:ef37fb04a343
 // Scala Lecture 1
 //=================
-println("Hello World")
+// Topics
+//--------
 // - List, Sets, Ints, Strings, ...
 // - Value assignments (val vs var)
 // - How to define functions? (What is returned?)
 // - If-Conditions
 // - For-Comprehensions (guards, with/without yield)
 // - String-Interpolations
 //
-//
 // Value assignments
 // (their names should be lower case)
 val s1 = Set(1,2,3,1)
 // picking an element in a list
 val lst = List(1, 2, 3, 1)
-val lst = List(1, 2, 3, 1)
 val lst1 = 0 :: lst
 println(lst)
 println(lst1)
 // ranges
 1 to 10
 (1 to 10).toList
 (1 to 10).toList.toString
-(1 until 10).toList
 // Equality in Scala is structural
 //=================================
 val a = "Dave2"
 if (l == 0) 0
 else s / l
 }
 average(List(1,2,3,4,56))
 def incr(x: Int) : Int = x + 1
 def double(x: Int) : Int = x + x
 def square(x: Int) : Int = x * x
 def str(x: Int) : String = x.toString
 len(List(1,2,3,4,1))
-def len(xs: List[Int]) : Int = xs match {
-case Nil => 0
-case x :: xs => 1 + len(xs)
-}
-len(List(1,2,3,4,1))
 // If-Conditionals
 //=================
-// - Scala used to not have a then-keyword
+// - Scala used to *not* have a then-keyword
 // - !!both if-else branches need to be present!!
 def fact(n: Int) : Int =
 if (n == 0) 1 else n * fact(n - 1)
+fact(5)
 // Scala 3 introduced if-then-else - maybe people
 // desperately needed it
 def fact(n: Int) : Int =
 if n == 0 then 1 else n * fact(n - 1)
-fact(5)
 fact(150)
 /* boolean operators
 ==     equals
 val mult_table =
 for (n <- (1 to 10).toList;
 m <- (1 to 10).toList) yield n * m
 println(mult_table.mkString(","))
-mult_table.sliding(10,10).toList.mkString(",")
+mult_table.sliding(10,10).toList.mkString("\n")
-.mkString("\n")
 // for-comprehensions also work for other
 // collections
 for (n <- Set(10,12,4,5,7,8,10)) yield n * n
 for (n <- (1 to 10)) yield {
 n * n
 }
 // with if-predicates / filters
 // with patterns
 val lst = List((1, 4), (2, 3), (3, 2), (4, 1))
-` yield m + n
 for (p <- lst) yield p._1 + p._2
+for ((m, n) <- lst) yield m + n
 // general pattern of for-yield
 // (yield can be several lines)
 //===================
 // with only a side-effect (no list is produced),
 // has no "yield"
-val xs = for (n <- (1 to 10).toList) yield println(n * n)
+val xs = for (n <- (1 to 10).toList) println(n * n)
-xs.tail
+xs.tail  // error
 val foo = for (n <- (1 to 10).toList) yield n * n
 println(for (n <- (1 to 10).toList)  print(n))
 // Aside: concurrency
-// scala-cli --extra-jars scala-parallel-collections_3-1.0.4.jar
+// scala --extra-jars scala-parallel-collections_3-1.2.0.jar
 for (n <- (1 to 10)) println(n)
 import scala.collection.parallel.CollectionConverters._
 import scala.collection.parallel.CollectionConverters._
 def test() = {
 var cnt = 0
-for(i <- (1 to 100_000)) cnt += 1
+for(i <- (1 to 100_000).par) cnt += 1
-println(s"Should be 100000: $cnt")
+println(s"Should be 100_000: $cnt")
 }
 test()
 // Or

changeset 497	ef37fb04a343
parent 491	2a30c7dfe3ed