stephenLee

val capitals = Map("France" -> "Paris", "Japan" -> "Tokyo")
capitals get "France"
capitals get "North Pole"

def show(x: Option[String]) = x match {
  case Some(x) => x
  case None => "?"
}

show(capitals get "Japan")

stephenLee

val capitals = Map("France" -> "Paris", "Japan" -> "Tokyo")
capitals get "France"
capitals get "North Pole"

def show(x: Option[String]) = x match {
  case Some(x) => x
  case None => "?"
}

show(capitals get "Japan")

stephenLee

abstract class Expr 
case class Var(name: String) extends Expr
case class Number(num: Double) extends Expr
case class UnOp(operator: String, arg: Expr) extends Expr
case class BinOp(operator: String, left: Expr, right: Expr) extends Expr

val v = Var("x")
val op = BinOp("+", Number(1), v)

v.name

stephenLee

import scala.collection.mutable.ArrayBuffer

//Abstract class IntQueue
abstract class IntQueue {
  def get(): Int 
  def put(x: Int)
}

// A BasicIntQueue implemented with an ArrayBuffer
class BasicIntQueue extends IntQueue {

stephenLee

def curriedSum(x: Int)(y: int) = x + y
curriedSum(1)(2)  // 3


def first(x: Int) = (y: Int) => x + y
val second = first(1)
second(2) // 3

// use placeholder notation to use curriedSum in a partially applied function

stephenLee

def sum(a: Int, b: Int, c: Int): Int = a + b + c

val a = sum _
a(1,2,3）

val b = sum(1, _: Int, 3)
b(2)
b(5)

stephenLee

/**
 * place an asterisk after the type of the parameter
 */
def echo(args: String*) = 
  for (arg <- args) printn(arg)

echo("hello", "world")

val arr = Array("What's", "up", "doc?")
echo(arr: _*)

stephenLee

class Rational(n: Int, d: Int) {
  require(d != 0)

  private val g = gcd(n.abs, d.abs)
  val number = n / g
  val denom = d / g
  
  def this(n: Int) = this(n, 1) // auxiliary constructor
  
  def + (that: Rational): Rational = 

stephenLee

def factorial(n: Int): Int = {
   if (n==0) 1 else n * factorial(n-1)
}

stephenLee

def factorial(n: Int) = {
  def factorial1(n: Int, multi: Int): Int = {
    if (n == 0) multi 
    else factorial1(n-1, multi*n)
  }
  factorial1(n, 1)
}