Introduction to Scala Part3: Option & Pattern Matching

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Option Data Type Methods of Option Create your own Option type

Pattern Matching

Pattern matching is a generalization of switch from C/Java to class hierarchies. It’s expressed in Scala using the keyword match.

Examples:

def eval(e: Expr): Int = e match {
    case Number(n) => n
    case Sum(e1, e2) => eval(e1) + eval(e2)
}

Rules

Match is followed by a sequence of cases
Each case associates an expression to a pattern
An exception MatchError is thrown if no pattern matches the value of the selector

Pattern forms

Patterns are constructed from:

Constructors : Number, Sum, etc.
Variables : n, e1, e2, etc.
Wildcard patterns : _
Constants : 1 , true

Variables always begin with a lowercase letter. The same variable name can only appear once in a pattern (Sum(x, x) is not a legal pattern)

Constructors and the names of constants begin with a capital letter, with the exception of the reserved words: null, true ,false

headOption

sum

multiply

fibonacci

lastOption

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package fp101.tp03.patternmatching
object ExercicePatternMatching {
  /**
   * 
   * Use list match { ...}
   */
  def headOption[T](list: List[T]): Option[T] = ???
  /**
   * 
   * Use l match { ...}
   */
  def sum(list: List[Int]): Int = ???
  /**
   * 
   * Use list match {... }
   */
  def multiply(list: List[Int]): Int = ???
  /**
   * 
   * use n match {...}
   * fibonacci(n) = fibonacci(n -1) + fibonacci(n - 2)
   * base: fibonacci(0) => 0
   * fibonacci(1) => 1
   * fibonacci(< 0) => 0
   * 
   */
  def fibonacci(n: Int): Int =  ???
  /**
   * use l match {...}
   * This is harder.
   * You have to read the documentation of List to find the good operation of composition
   * 
   * http://www.scala-lang.org/api/current/#scala.collection.immutable.List

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