pep-material: comparison progs/lecture1.scala

equal deleted inserted replaced

-:244df77507c2
+:253d1ccb65de
 // Scala Lecture 1
 //=================
+println("Hello World")
 // - List, Sets, Ints, Strings, ...
 // - Value assignments (val vs var)
 // - How to define functions? (What is returned?)
 // - If-Conditions
 // - String-Interpolations
 //
 //
 // Value assignments
 // (their names should be lower case)
 //====================================
 val x = 42
 val y = 3 + 4
 val z = x / y
-val x = 0
+val x = 17
 println(z)
 // (you cannot reassign values: z = 9 will give an error)
-var z = 9
-z = 10
 // Collections
 //=============
-List(1,2,3,1)
+val ls = List("1","2","3","1")
-Set(1,2,3,1)
+val ls2 = ls ::: ls
+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)
 lst(0)
 lst(2)
 // head and tail
 1 :: 2 :: 3 :: Nil
 List(1, 2, 3) ::: List(4, 5, 6)
 // also
-List(1, 2, 3) ++ List(3, 6, 5)
+List(1, 2, 3) ::: List(3, 6, 5)
 Set(1, 2, 3) ++ Set(3, 6, 5)
 // ranges
 1 to 10
 (1 to 10).toList
 // you can make the type of a value explicit
 val name = "bob"
-val name : String = "bob"
+val name : Int = "bob"
 // type errors
 math.sqrt("64")
 // produces
 // Function Definitions
 //======================
+// The general scheme for a function: you have to give a
+// type to each argument and a return type of the function
+//
+//  def fname(arg1: ty1, arg2: ty2,..., argn: tyn): rty = {
+//     ....
+//  }
+def average(ls: List[Int]) : Int = {
+println(s"$ls")
+val s = ls.sum
+val l = ls.length
+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
 incr(3)
 double(4)
 square(6)
 str(3)
-// The general scheme for a function: you have to give a
-// type to each argument and a return type of the function
-//
+def len(xs: List[Int]) : Int = {
-//  def fname(arg1: ty1, arg2: ty2,..., argn: tyn): rty = {
+if (xs == Nil) 0
-//     ....
+else 1 + len(xs.tail)
-//  }
+}
-// > LENGTH OF LIST EXAMPLE
-def len(xs: List[Int], acc: Int) : Int = {
-if (xs == Nil) acc
-else foo(xs.tail, acc + 1)
-}
-def len(xs: List[Int]) : Int = foo(xs, 0)
 len(List(1,2,3,4,1))
-def len(xs: List[Int]) : Int = {
-if (xs == Nil) 0
-else (1 + len(xs.tail))
-}
-len(List(1,2,3,4,1))
 def len(xs: List[Int]) : Int = xs match {
 case Nil => 0
 // For-Comprehensions (not For-Loops)
 //====================================
-val lst = (1 to 10).toList
+val lst = (1 to 10).toSet
-for (n <- lst) yield n * n
+val result = for (n <- lst) yield {
+n * n
+}
+println(result)
 for (n <- lst) yield {
 square(n) + double(n)
 }
 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
+mult_table.sliding(10,10).toList.mkString(",")
 .mkString("\n")
 // for-comprehensions also work for other
 // with if-predicates / filters
 val xs = for (n <- (1 to 3).toList;
 m <- (1 to 3).toList) yield (n,m)
-xs.filter{case (m, n) => (n + m) % 2 == 0}
 for (n <- (1 to 3).toList;
 m <- (1 to 3).toList;
 if (n + m) % 2 == 0) yield (n, m)
 xs.tail
 val foo = for (n <- (1 to 10).toList) yield n * n
+println(for (n <- (1 to 10).toList)  print(n))
 // BTW: a roundabout way of printing out a list, say
 val lst = ('a' to 'm').toList
 for (i <- (0 until lst.length)) println(lst(i))
 // .maxBy, sortBy with pairs
 def get_length(s: String) : (String, Int) =
 (s, s.length)
+def len(s: String) : Int = s.length
 val lst = List("zero", "one", "two", "three", "four", "ten")
+lst.sorted
+lst.sortBy(len(_))
 val strs = for (s <- lst) yield get_length(s)
 strs.sortBy(_._2)
 strs.sortBy(_._1)
 // - no mutable data-structures (no Arrays, no ListBuffers)
 // But what the heck....lets try to count to 1 Mio in parallel
 //
 // requires
-// scala-cli --extra-jars scala- parallel-collections_3-1.0.4.jar
+// scala --extra-jars scala- parallel-collections_3-1.0.4.jar
 import scala.collection.parallel.CollectionConverters._
 def test() = {
 var cnt = 0
 l"some_fresh_name"
 // Further Information
 //=====================
-// We are going to use Scala 3 and the scala-cli repl (easier to use)
+// We are going to use Scala 3. The Scala homepage
-//
+// and general information is at
-//  https://scala-cli.virtuslab.org
-//
-//
-// The Scala homepage and general information is at
 //
 //  http://www.scala-lang.org
 //	http://docs.scala-lang.org
 //
 //
-// It should be fairly easy to install the scala-cli binary and
+// It should be fairly easy to install the scala binary and
 // run Scala on the commandline. People also use Scala with
-// Vim and Jedit. I currently settled on Codium
+// Vim and Jedit. I currently settled on Codium / VSCode
 //
+//   https://vscodium.com
 //   https://code.visualstudio.com
 //
 // There are also plugins for Eclipse and IntelliJ - YMMV.
 // Finally there are online editors specifically designed for
 // running Scala applications (but do not blame me if you lose
 // all what you typed in):
 //
-//   https://scalafiddle.io
 //   https://scastie.scala-lang.org
 //
 //
 //
 // Scala Library Docs

changeset 494	253d1ccb65de
parent 481	e03a0100ec46