pep-material: comparison progs/lecture1.scala

equal deleted inserted replaced

-:40147ad17bdf
+:006f71e905a1
 // Scala Lecture 1
 //=================
 // Value assignments
-// (variable names should be lower case)
+// (their names should be lower case)
-//======================================
+//===================================
 val x = 42
 val y = 3 + 4
+val z = x / y
+// (you cannot reassign values: z = 9 will give an error)
 // Collections
 //=============
 List(1,2,3,1)
 List(1,2,3,4).max
 List(1,2,3,4).min
 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)
+List(1,2,3,4,3)indexOf(3)
 "1,2,3,4,5".split(",").mkString("\n")
 "1,2,3,4,5".split(",3,").mkString("\n")
 // Types
 // Function Definitions
 //======================
-def square(x: Int): Int = x * x
+def incr(x: Int) : Int = x + 1
+def double(x: Int) : Int = x + x
+def square(x: Int) : Int = x * x
 square(6)
 //    body
 //  }
-// If control structure
+// If-Conditionals
-//======================
+//=================
 def fact(n: Int): Int =
 if (n == 0) 1 else n * fact(n - 1)
 if (n == 1) 1 else fib(n - 1) + fib(n - 2)
 //gcd - Euclid's algorithm
-def gcd(a: Int, b: Int): Int =
+def gcd(a: Int, b: Int) : Int =
 if (b == 0) a else gcd(b, a % b)
 gcd(48, 18)
+def power(x: Int, n: Int) : Int =
+if (n == 0) 1  else x * power(x, n - 1)
+power(5, 5)
 // String Interpolations
 //=======================
 println(s"The square of ${n} is ${square(n)}.")
-def gcd_db(a: Int, b: Int): Int = {
+def gcd_db(a: Int, b: Int) : Int = {
 println(s"Function called with ${a} and ${b}.")
 if (b == 0) a else gcd_db(b, a % b)
 }
 gcd_db(48, 18)
 //==========
 import io.Source
 // obtaining a webpage
-val url = """http://www.inf.kcl.ac.uk/staff/urbanc/"""
+val url = """https://nms.kcl.ac.uk/christian.urban/"""
 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"
+val url = "https://download.finance.yahoo.com/d/quotes.csv?s=" + symbol + "&f=snl1"
 Source.fromURL(url).mkString.drop(1).dropRight(2)
 }
 price_lookup("GOOG")
 price_lookup("AAPL")
 val companies =
 List("GOOG", "AAPL", "MSFT", "IBM", "FB", "YHOO", "AMZN", "BIDU")
-for (s <- companies.par) println(price_lookup(s))
+for (s <- companies) println(price_lookup(s))
 // A Web Crawler
 //===============
 //
-// the idea is to look for dead links
+// the idea is to look for dead links using the
+// regular expression "https?://[^"]*"
 import io.Source
 import scala.util.matching.Regex
 import scala.util._
 for (u <- get_all_URLs(get_page(url))) crawl(u, n - 1)
 }
 }
 // some starting URLs for the crawler
-val startURL = """http://www.inf.kcl.ac.uk/staff/urbanc"""
+val startURL = """https://nms.kcl.ac.uk/christian.urban/"""
 //val startURL = """http://www.inf.kcl.ac.uk/staff/mcburney"""
 crawl(startURL, 2)
 // Further Information
 //=====================
-// Scala download
+// The Scala home page and general information is at
 //
 //  http://www.scala-lang.org
+//	http://docs.scala-lang.org
-// Eclipse for Scala
+//
 //
-//  http://scala-ide.org/download/sdk.html
+// It should be fairly easy to install the Scala binary and
+// run Scala on the commandline. There are also at least
+// four IDEs you can use with Scala:
-// library docs
+//
+//  (0) Some general information for setting up IDEs
+//	    with Scala support can be found at
+//
+//         http://docs.scala-lang.org/getting-started.html
+//
+//  (1) Eclipse for Scala (one big bundle)
+//
+//         http://scala-ide.org/download/sdk.html
+//
+//  (2) IntelliJ (needs additional Plugins)
+//
+//         https://www.jetbrains.com/idea/
+//		   http://docs.scala-lang.org/getting-started-intellij-track/getting-started-with-scala-in-intellij.html
+//
+//  (3) Sublime (not free, but unlimited trial period;
+//	    needs SublimeREPL plugin)
+//
+//         https://www.sublimetext.com
+//
+//  (4) Emacs (old-fashioned, but reliable)
+//
+//         https://www.gnu.org/software/emacs/
+//
+//      I use the old scala-tool support for Emacs distributed at
+//
+//         https://github.com/scala/scala-tool-support/tree/master/tool-support/emacs
+//
+//      but there is also support for the newer Ensime Scala Mode
+//
+//         http://ensime.org/editors/emacs/scala-mode/
+//
+// There is also Scala support in the Atom editor, but my
+// experience is mixed. People also use Scala with Vim and Jedit.
+//
+// All of the IDEs above support a REPL for Scala. Some of them have
+// the very nifty feature of a Scala Worksheet -- you just save your
+// file and it will be automatically evaluated and the result pasted
+// into your file. However, this way of writing Scala code never worked
+// for me. I just use the REPL.
+//
+//
+// Scala Library Docs
 //
 //  http://www.scala-lang.org/api/current/
+//
-// tutorials
+// Scala Tutorials
 //
 //  http://docs.scala-lang.org/tutorials/
+//
+// There are also a massive number of Scala tutorials on youtube
+// and there are tons of books and free material.
+//

changeset 123	006f71e905a1
parent 51	0e60e6c24b99
child 124	880e92e5b604