// useful list methods

List(1,2,3,4).length

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)

"1,2,3,4,5".split(",").toList

// an example of a stand-alone scala file;

// in the coursework students must submit 

// plain scala "work-sheets"

object Hello extends App { 

  println("hello world")

}

// can be called with

//

// $> scalac hello-world.scala

// $> scala Hello

//

// $> java -cp /usr/local/src/scala/lib/scala-library.jar:. Hello

assert(gcd(48, 18) == 6)

assert(gcd(48, 18) == 5, "The gcd test failed")

// with if-predicates

for (n <- (1 to 3).toList; 

     m <- (1 to 3).toList;

     if (n + m) % 2 == 0) yield (n, m)

// 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)

for (n <- (1 to 10)) println(n)

for (n <- (1 to 10).par) println(n)

// 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"

}

val list = (1 to 1000000).toList

time_needed(10, for (n <- list) yield n + 42)

time_needed(10, for (n <- list.par) yield n + 42)

import io.Source

val url = """http://www.inf.kcl.ac.uk/staff/urbanc/""" 

Source.fromURL(url)("ISO-8859-1").mkString

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)

}

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))

// A Web Crawler

//===============

import io.Source

import scala.util.matching.Regex

import scala.util._

// gets the first 10K of a web-page

def get_page(url: String) : String = {

  Try(Source.fromURL(url)("ISO-8859-1").take(10000).mkString).

    getOrElse { println(s"  Problem with: $url"); ""}

}

// regex for URLs

val http_pattern = """"https?://[^"]*"""".r

// drops the first and last character from a string

def unquote(s: String) = s.drop(1).dropRight(1)

def get_all_URLs(page: String): Set[String] = 

  http_pattern.findAllIn(page).map(unquote).toSet

// naive version of crawl - searches until a given depth,

// visits pages potentially more than once

def crawl(url: String, n: Int): Unit = {

  if (n == 0) ()

  else {

    println(s"Visiting: $n $url")

    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 = """http://www.inf.kcl.ac.uk/staff/mcburney"""

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

//

//  http://www.scala-lang.org

// Eclipse for Scala

//

//  http://scala-ide.org/download/sdk.html

// library docs

//

//  http://www.scala-lang.org/api/current/

// tutorials

//

//  http://docs.scala-lang.org/tutorials/