Question

trying to run the sample code in the Apress book called “Beginning Scala”. I even downloaded the code from their website to make sure I didn’t goof. Getting the following message:

/root/sum.scala:19: error: missing arguments for method collect in trait Iterator;
follow this method with `_' if you want to treat it as a partially applied function
val lines = input.getLines.collect 
                           ^
one error found

and here is the source code i used (running Scala version 2.8.1.final (Java HotSpot(TM) Server VM, Java 1.6.0_22 on Fedora 13)

import scala.io._

def toInt(in: String): Option[Int] =
  try {
    Some(Integer.parseInt(in.trim))
  } catch {
    case e: NumberFormatException => None
  }

def sum(in: Seq[String]) = {
  val ints = in.flatMap(s => toInt(s))
  ints.foldLeft(0)((a, b) => a + b)
}

println("Enter some numbers and press ctrl-D (Unix/Mac) ctrl-C (Windows)")

val input = Source.fromInputStream(System.in)

val lines = input.getLines.collect

println("Sum "+sum(lines))

looks like this is the relevant change:

The Iterator.collect() method in 2.7.7 returns a Seq. In 2.8, it is used to perform a conditional map using a PartialFunction. You can use input.getLines.toSeq instead.

Answer 1

Ah, I remember this:

EDIT: replaced with more in depth answer

The code was written against Scala
2.7.3 and 2.8 introduces some breaking changes.

Here’s an update to the code that
works under Scala 2.8.0:

import scala.io._

object Sum {
  def main(args: Array[String]): Unit = {
    println("Enter some numbers and press ctrl-D (Unix/Mac) ctrl-Z (Windows)")
    val input = Source.fromInputStream(System.in)
    val lines = input.getLines.toList
    println("Sum " + sum(lines))
  }

  def toInt(s: String): Option[Int] = {
    try {
      Some(Integer.parseInt(s))
    } catch {
        case e: NumberFormatException => None
    }
  }

  def sum(in: Seq[String]): Int = {
    val ints = in.flatMap(toInt(_))
    ints.foldLeft(0)((a, b) => a + b)
  }

}

Source: http://scala-programming-language.1934581.n4.nabble.com/Beginning-Scala-book-problem-td2966867.html