pep-material: comparison progs/lecture1.scala

equal deleted inserted replaced

-:40424bbe109e
+:f5ed0fef41b3
 List(1,2,3,4).sum
 List(1,2,3,4).take(2).sum
 List(1,2,3,4).drop(2).sum
 List(1,2,3,4,3).indexOf(3)
-"1,2,3,4,5".split(",").toList
+"1,2,3,4,5".split(",").mkString("\n")
+"1,2,3,4,5".split(",3,").mkString("\n")
 // Types
 //=======
 /* Scala is a strongly typed language
 */
 // Smart Strings
 //===============
-println(">\n<")
+println(">\n\n<")
 println(""">\n<""")
+println("""">\n<"""")
 /* in Java
 val lyrics = "Baa, Baa, Black Sheep \n" +
 "Have you any wool? \n" +
 "Yes, sir, yes sir \n" +
 def square(x: Int): Int = x * x
 square(6)
+// 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 = {
+//    body
+//  }
 // If control structure
 //======================
 def fact(n: Int): Int =
 if (n == 0) 1 else n * fact(n - 1)
+fact(5)
+fact(150)
 /* boolean operators
 ==     equals
 !      not
 for (p <- List((1, 4), (2, 3), (3, 2), (4, 1))) yield p._1 + p._2
-// with only a side-effect (no list is produced)
+// with only a side-effect (no list is produced),
 // has no "yield"
 for (n <- (1 to 10)) println(n)
-// concurrency (ONLY WORKS IN 2.11.8)
+// concurrency (ONLY WORKS IN SCALA 2.11.8, not in SCALA 2.12.0)
 for (n <- (1 to 10)) println(n)
 for (n <- (1 to 10).par) println(n)
+// for measuring time
-// for testing time
 def time_needed[T](i: Int, code: => T) = {
 val start = System.nanoTime()
 for (j <- 1 to i) code
 val end = System.nanoTime()
 ((end - start) / i / 1.0e9) + " secs"
 // Webpages
 //==========
 import io.Source
+// obtaining a webpage
 val url = """http://www.inf.kcl.ac.uk/staff/urbanc/"""
 Source.fromURL(url)("ISO-8859-1").mkString
+// function for looking up stockmarket data
 def price_lookup(symbol: String): String = {
 val url = "http://finance.yahoo.com/d/quotes.csv?s=" + symbol + "&f=snl1"
 Source.fromURL(url).mkString.drop(1).dropRight(2)
 }
 for (s <- companies.par) println(price_lookup(s))
 // A Web Crawler
 //===============
+//
+// the idea is to look for dead links
 import io.Source
 import scala.util.matching.Regex
 import scala.util._
 crawl(startURL, 2)
-// Adding your own methods to Strings
-//====================================
-// imagine you want to implement an additional
-// method to strings, like
-//
-//     "HAL".increment
-//
-// you can avoid ugly fudges, like a MyString
-// class by using implicit conversions
-implicit class MyString(s: String) {
-def increment = for (c <- s) yield (c + 1).toChar
-}
-"HAL".increment
 // Further Information
 //=====================
 // Scala download
 //

changeset 36	f5ed0fef41b3
parent 34	40424bbe109e
child 51	0e60e6c24b99