Boston Area Scala Enthusiasts fourth meeting held on Feb 2, 2010. Talk delivered by Nermin Serifovic.

1. Boston Area Scala Enthusiasts Implementing IN operator in Scala Nermin Serifovic February 2, 2010

2. Pascal provides the in operator: if 5 in [1, 2, 3, 4, 5, 6] then write (“5 is in the set”); SQL allows it too: Select * From Employees Where LastName IN (‘Smith’, ‘Garcia’, ‘Johnson’, ‘Lee’)

3. Ideally, would like to write something like this in Scala: if (5 in [1, 2, 3]) foundIt = true Or: if (5 in (1, 2, 3)) foundIt = true Valid in Groovy: def list = [5, 6, 7, 8] However, Scala has no literals for Lists, Sets, etc… All brackets and parenthesis are already reserved: []: type parameterization (): tuples {}: code block <>: relational methods

4. Acceptable syntax: if (5 in List(1, 2, 3)) foundIt = true or: if (“Scala” in Array(“Programming”, “in”, “Scala”) foundIt = true Extra credit: if (5 not in List(1, 2, 3)) foundIt = false instead of: if !(5 in List(1, 2, 3)) foundIt = false

5. Operands.scala: package in.nerm.scala.ltalk1 class InOperand[A](a: A) { def in(seq: Seq[A]): Boolean = seq.contains(a) } object OperandConversions { implicit def toInOperand[A](a: A): InOperand[A] = new InOperand(a) } Note: parameterized, so it’s not possible to say: if (5 in List(“white”, “blue”) foundIt = true

6. InOperandTests.scala: package in.nerm.scala.ltalk1 import in.nerm.scala.ltalk1.OperandConversions._ import org.testng.annotations.Test import org.scalatest.testng.TestNGSuite class InOperandTests extends TestNGSuite { @Test def verifyIn() { assert(5 in List(1, 2, 3, 4, 5, 6)) assert(!(7 in Array(1, 2, 3, 4, 5, 6))) assert("Scala" in List("Programming", "in", "Scala")) } }

7. Given that: 5 not in List(1, 2, 3) gets interpreted as: 5.not(in).List(1, 2, 3) is it really possible to implement it? If not, how close can we get?