scala/java version. About 11sec

py-vs-haskell.scala

import scala.io._
import java.io._
import scala.collection.mutable.ArrayBuffer

object Main {
	def main(args: Array[String]): Unit = {
		var i = 0
		var v1: ArrayBuffer[String] = new ArrayBuffer(10000)
		var v2: ArrayBuffer[String] = new ArrayBuffer(10000)
		Source.stdin.getLines.foreach{
			x => 
				val arr = x.split(' ')
				v1 += arr(0)
				v2 += arr(1)
				i += 1
		}
				
		val writer = new PrintWriter(System.out)
		for {
			x <- v1
			y <- v2
		} yield writer.write(x + y + "\n")

		writer.flush()
		writer.close()
	}
}