REPL after the Gentle Scala Introduction @ Sytac DevJam

scala-intro-devjam.scala

/**
 * For the first part I had to rely on the repl history as the console buffer was gone after the stack overflow of factorial 
 */ 
val i = 10
:type i
val i: Int = 10
val s = "Ciao"
i = 4
var j = 20
j = 10
val i: Int = 5
i = 6
var j: Int = 6
j = 8
val k = 8
val s = "Piero"
s == "Piero"
1 + 2
1.+(2)
def add(x: Int, y: Int) = x + y

def add(x: Int, y: Int) = {
 x = 0
 x + y
}

val x = 1
x + 5
x.+(5)
class Point(x: Double, y: Double)
class Point(x: Double, y: Double) {
def +(other: Point): Point = new Point(x + other.x, y + other.y)
}
class Point(val x: Double, val y: Double) {
def +(other: Point): Point = new Point(x + other.x, y + other.y)
}
val p1 = new Point(4,5)
val p2 = new Point(3,4)
p1.+(p2)
class Point(val x: Double, val y: Double) {
def +(other: Point): Point = new Point(x + other.x, y + other.y)
override def toString() = "Point(" + x + "," + y + ")"
}
val p1 = new Point(4,5)
val p2 = new Point(3,4)
p1.+(p2)
p1 + p2
val mul = (x: Int, y: Int) => x * y
:type mul
mul(4,5)
def mul2(x: Int, y: Int) = x * 2
def mul2(x: Int, y: Int) = x * y
mul2(4,5)
val add4 = new Function[Int, Int] {
def apply(x: Int): Int = x + 4
}
add4.apply(8)
add4(8)
val environment = "prod"
val dbUrl = if (environment == "prod") "jdbc...prod" else "jbdc...test"
val add2 = (x: Int) => x + 2
val mul5 = (x: Int) => x * 5
val comp = add2.compose(mul5)
comp(2)
val comp = add2 compose mul5
val comp2 = mul5 andThen add2
def fact(n: BigInt): BigInt = {
if (n == 1) n
else n * fact(n - 1)
}
fact(3)
fact(10)
fact(20000) // BOOM!
scala> def fact(n: BigInt): BigInt = {
     | else n * fact(n - 1)
<console>:2: error: illegal start of statement
else n * fact(n - 1)
^

scala> def fact(n: BigInt): BigInt = {
     | if (n == 1) n
     | else n * fact(n - 1)
     | }
fact: (n: BigInt)BigInt

scala> def fact2(n: BigInt): BigInt = {
     | def go(acc: BigInt, k: BigInt) = {
     | if (k == 1) acc else go(k * acc, k - 1)
     | }
     | 
     | 
You typed two blank lines.  Starting a new command.

scala> def fact2(n: BigInt): BigInt = {
     | def go(acc: BigInt, k: BigInt): BigInt = {
     | if (k == 1) acc else go(k * acc, k - 1)
     | }
     | go(1, n)
     | }
fact2: (n: BigInt)BigInt

scala> fact2(3)
res16: BigInt = 6

scala> fact2(5)
res17: BigInt = 120

scala> fact2(20000)
res18: BigInt = 1819206320230345134827641756866458766071609901478752648918062218634569461038557534453836095827758724739177502384189912041671245383926576865723475464524930275709204625357875789525900491823414542718036070392521085047283383729296861580052404638841199526622379791066223341463393474395925629787482113163418647665455586660436184087223951946276615548561632208981651545091872218436294406051877306392783358445931186417148398260080400146928105895643738692767105374763186090336511780868599512519843617384918221869858019078196339128759665295841157777813491489409939230578103105905988720691493952696699343574983659137962578903705716902337854828253406978492916531166704020223408974723378025728021785188391510797310297013143732956206337141728256129448819212285111707757412048942243223685263626707...

scala> val numbers = List(4,2,6,8,9,4)
numbers: List[Int] = List(4, 2, 6, 8, 9, 4)

scala> val strings: List[String] = List("Piero", "Carlo", "Davide")
strings: List[String] = List(Piero, Carlo, Davide)

scala> val strings: List[String] = List(1,2,3)
<console>:10: error: type mismatch;
 found   : Int(1)
 required: String
       val strings: List[String] = List(1,2,3)
                                        ^
<console>:10: error: type mismatch;
 found   : Int(2)
 required: String
       val strings: List[String] = List(1,2,3)
                                          ^
<console>:10: error: type mismatch;
 found   : Int(3)
 required: String
       val strings: List[String] = List(1,2,3)
                                            ^

scala> 

scala> 

scala> def sum(ns: List[Int]): Int = {
     | var res = 0
     | for {
     | i <- ns
     | } res + 1
     | res
     | }
sum: (ns: List[Int])Int

scala> sum(numbers)
res19: Int = 0

scala> def sum(ns: List[Int]): Int = {
     | var res = 0
     | for {
     | i <- ns
     | } res = res + i
     | res
     | }
sum: (ns: List[Int])Int

scala> sum(numbers)
res20: Int = 33

scala> def sumRec(ns: List[Int]): Int = {
     | if (ns.isEmpty()) 0
     | else ns(0) + sumRec(ns.tail)
     | }
<console>:11: error: Boolean does not take parameters
       if (ns.isEmpty()) 0
                     ^

scala> def sumRec(ns: List[Int]): Int = {
     | if (ns.isEmpty) 0
     | else ns(0) + sumRec(ns.tail)
     | }
sumRec: (ns: List[Int])Int

scala> sumRec(numbers)
res21: Int = 33

scala> def sumFold(ns: List[Int]): Int = {
     | ns.foldLeft(0)((x: Int, y: Int) => x + y)
     | }
sumFold: (ns: List[Int])Int

scala> sumFold(numbers)
res22: Int = 33

scala> def sumFoldR(ns: List[Int]): Int = ns.foldRight(0)(_ + _)
sumFoldR: (ns: List[Int])Int

scala> sumFoldR(numbers)
res23: Int = 33

scala> sumFoldR(List())
res24: Int = 0

scala> numbers.foldRight(5)(_ + _)
res25: Int = 38

scala> numbers.foldRight(5)(_ - _)
res26: Int = 10

scala> numbers.foldLeft(5)(_ - _)
res27: Int = -28

scala> numbers
res28: List[Int] = List(4, 2, 6, 8, 9, 4)

scala> numbers.foldLeft("")((x, y) => x + "," + y)
res29: String = ,4,2,6,8,9,4

scala> val empty = Nil
empty: scala.collection.immutable.Nil.type = List()

scala> List()
res30: List[Nothing] = List()

scala> val oneVal = List(1)
oneVal: List[Int] = List(1)

scala> val oneVal = 1 :: Nil
oneVal: List[Int] = List(1)

scala> numbers
res31: List[Int] = List(4, 2, 6, 8, 9, 4)

scala> 4 :: 2 :: 6 :: 8 :: 9 :: 4 :: Nil
res32: List[Int] = List(4, 2, 6, 8, 9, 4)

scala> :type ::
collection.immutable.::.type

scala> :type ::_
() => collection.immutable.::.type

scala> :type ::[Int]_
(Int, List[Int]) => scala.collection.immutable.::[Int]

scala> def sumPM(nrs: List[Int]) = nrs match {
     | case Nil => 0
     | case n :: ns => n + sumPM(ns)
     | }
<console>:12: error: recursive method sumPM needs result type
       case n :: ns => n + sumPM(ns)
                           ^

scala> def sumPM(nrs: List[Int]): Int = nrs match {
     | case Nil => 0
     | case n :: ns => n + sumPM(ns)
     | }
sumPM: (nrs: List[Int])Int

scala> sumPM(numbers)
res33: Int = 33

scala> def addFirst2(nrs: List[Int]): Int = nrs match {
     | case n0 :: n1 :: ns => n0 + n1
     | case _ => 0
     | }
addFirst2: (nrs: List[Int])Int

scala> addFirst2(List(1,2,3,4))
res34: Int = 3

scala> case class Point(x: Double, y: Double)
defined class Point

scala> val p1 = Point(3,4)
p1: Point = Point(3.0,4.0)

scala> val p2 = Point(5,6)
p2: Point = Point(5.0,6.0)

scala> 

scala> p1.x
res35: Double = 3.0

scala> val points = List(Point(3,4), Point(3,6), Point(8,7))
points: List[Point] = List(Point(3.0,4.0), Point(3.0,6.0), Point(8.0,7.0))

scala> point.filter { case Point(3, _) => true
     | case _ => false
     | }
<console>:13: error: not found: value point
       point.filter { case Point(3, _) => true
       ^

scala> points.filter { case Point(3, _) => true
     | case _ => false
     | }
res37: List[Point] = List(Point(3.0,4.0), Point(3.0,6.0))

scala> object Factory {
     | def giveString = "something"
     | }
defined object Factory

scala> Factory.giveString
res38: String = something

scala> val pair = (1, "Scala")
pair: (Int, String) = (1,Scala)

scala> def getIfEven(pair: (Int, String)) = pair match {
     | case (i, s) if i % 2 == 0 => s
     | case _ => "unmatched"
     | }
getIfEven: (pair: (Int, String))String

scala> getIfEven((2, "Java"))
res39: String = Java

scala> getIfEven((1, "Scala"))
res40: String = unmatched

scala> List("Scala", "Java", "Clojure", "C++", "Lisp")
res41: List[String] = List(Scala, Java, Clojure, C++, Lisp)

scala> val languages = List("Scala", "Java", "Clojure", "C++", "Lisp")
languages: List[String] = List(Scala, Java, Clojure, C++, Lisp)

scala> languages.groupBy(_.length)
res42: scala.collection.immutable.Map[Int,List[String]] = Map(5 -> List(Scala), 4 -> List(Java, Lisp), 7 -> List(Clojure), 3 -> List(C++))

scala> languages.filter(_.lenght < 5)
<console>:12: error: value lenght is not a member of String
       languages.filter(_.lenght < 5)
                          ^

scala> languages.filter(_.length < 5)
res44: List[String] = List(Java, C++, Lisp)

scala> languages.filter(_.length >= 5)
res45: List[String] = List(Scala, Clojure)

scala> languages.partition(_.length < 5)
res46: (List[String], List[String]) = (List(Java, C++, Lisp),List(Scala, Clojure))

/**
 * From this moment we turned into intellij Scala console
 */ 
/usr/lib/jvm/java-8-oracle/bin/java -Djline.terminal=NONE -Didea.launcher.port=7533 -Didea.launcher.bin.path=/home/pierangeloc/tools/idea-IU-143.1821.5/bin -Dfile.encoding=UTF-8 -classpath /home/pierangeloc/platforms/activator-dist-1.3.7/repository/org.scala-lang/scala-compiler/2.11.6/jars/scala-compiler.jar:/home/pierangeloc/platforms/activator-dist-1.3.7/repository/org.scala-lang/scala-library/2.11.6/jars/scala-library.jar:/home/pierangeloc/platforms/activator-dist-1.3.7/repository/org.scala-lang/scala-reflect/2.11.6/jars/scala-reflect.jar:/home/pierangeloc/.IntelliJIdea15/config/plugins/Scala/lib/scala-plugin-runners.jar:/usr/lib/jvm/java-8-oracle/jre/lib/charsets.jar:/usr/lib/jvm/java-8-oracle/jre/lib/deploy.jar:/usr/lib/jvm/java-8-oracle/jre/lib/ext/cldrdata.jar:/usr/lib/jvm/java-8-oracle/jre/lib/ext/dnsns.jar:/usr/lib/jvm/java-8-oracle/jre/lib/ext/jaccess.jar:/usr/lib/jvm/java-8-oracle/jre/lib/ext/jfxrt.jar:/usr/lib/jvm/java-8-oracle/jre/lib/ext/localedata.jar:/usr/lib/jvm/java-8-oracle/jre/lib/ext/nashorn.jar:/usr/lib/jvm/java-8-oracle/jre/lib/ext/sunec.jar:/usr/lib/jvm/java-8-oracle/jre/lib/ext/sunjce_provider.jar:/usr/lib/jvm/java-8-oracle/jre/lib/ext/sunpkcs11.jar:/usr/lib/jvm/java-8-oracle/jre/lib/ext/zipfs.jar:/usr/lib/jvm/java-8-oracle/jre/lib/javaws.jar:/usr/lib/jvm/java-8-oracle/jre/lib/jce.jar:/usr/lib/jvm/java-8-oracle/jre/lib/jfr.jar:/usr/lib/jvm/java-8-oracle/jre/lib/jfxswt.jar:/usr/lib/jvm/java-8-oracle/jre/lib/jsse.jar:/usr/lib/jvm/java-8-oracle/jre/lib/management-agent.jar:/usr/lib/jvm/java-8-oracle/jre/lib/plugin.jar:/usr/lib/jvm/java-8-oracle/jre/lib/resources.jar:/usr/lib/jvm/java-8-oracle/jre/lib/rt.jar:/home/pierangeloc/Documents/projects/scala/presentations/scala-gentle-intro/target/scala-2.11/classes:/home/pierangeloc/.ivy2/cache/com.typesafe/config/bundles/config-1.2.1.jar:/home/pierangeloc/platforms/activator-dist-1.3.7/repository/com.typesafe.akka/akka-actor_2.11/2.3.11/jars/akka-actor_2.11.jar:/home/pierangeloc/platforms/activator-dist-1.3.7/repository/com.typesafe.akka/akka-testkit_2.11/2.3.11/jars/akka-testkit_2.11.jar:/home/pierangeloc/.ivy2/cache/org.scala-lang/scala-reflect/jars/scala-reflect-2.11.2.jar:/home/pierangeloc/.ivy2/cache/org.scala-lang.modules/scala-xml_2.11/bundles/scala-xml_2.11-1.0.2.jar:/home/pierangeloc/.ivy2/cache/org.scalatest/scalatest_2.11/bundles/scalatest_2.11-2.2.4.jar:/home/pierangeloc/tools/idea-IU-143.1821.5/lib/idea_rt.jar com.intellij.rt.execution.application.AppMain org.jetbrains.plugins.scala.compiler.rt.ConsoleRunner -usejavacp
Welcome to Scala version 2.11.6 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_66).
Type in expressions to have them evaluated.
Type :help for more information.

scala> 
class Person(val name: String, val surname: String) {
  assert(name.length > 5)
  override def toString = name + " " + surname
  
}
     |      |      |      | defined class Person

scala> new Person("Richard", "Feynman")
res0: Person = Richard Feynman

scala> new Person("Rick", "Feynman")
java.lang.AssertionError: assertion failed
  at scala.Predef$.assert(Predef.scala:151)
  ... 36 elided

scala> 
asdf
<console>:8: error: not found: value asdf
              asdf
              ^

scala> val languages = List("Scala", "Java", "Clojure", "C++", "Lisp")
languages: List[String] = List(Scala, Java, Clojure, C++, Lisp)

scala> languages.partition(_.length > 5)
res3: (List[String], List[String]) = (List(Clojure),List(Scala, Java, C++, Lisp))

scala> val lengthOf = (s: String) => s.length
lengthOf: String => Int = <function1>

scala> lengthOf("Scala")
res4: Int = 5

scala> 
languages.map(lengthOf)
res5: List[Int] = List(5, 4, 7, 3, 4)

scala> case class Point(x: Double, y: Double)
defined class Point

scala> val points = List(Point(3,4), Point(4,5), Point(9,8))
points: List[Point] = List(Point(3.0,4.0), Point(4.0,5.0), Point(9.0,8.0))

scala> points.map(p => p.x)
res6: List[Double] = List(3.0, 4.0, 9.0)

scala> points.map(_.x)
res7: List[Double] = List(3.0, 4.0, 9.0)

scala> val numbers = List(3,4,7,3,1,8,89,4)
numbers: List[Int] = List(3, 4, 7, 3, 1, 8, 89, 4)

scala> numbers.take(3)
res8: List[Int] = List(3, 4, 7)

scala> numbers.drop(3)
res9: List[Int] = List(3, 1, 8, 89, 4)

scala> numbers.takeWhile(_ < 10)
res10: List[Int] = List(3, 4, 7, 3, 1, 8)

scala> numbers.dropWhile(_ < 10)
res11: List[Int] = List(89, 4)

scala> numbers.filter( _ < 5)
res12: List[Int] = List(3, 4, 3, 1, 4)

scala> 
numbers.sum
res13: Int = 119

scala> val names = List("Richard", "Albert", "Alice")
names: List[String] = List(Richard, Albert, Alice)

scala> names.sum
<console>:9: error: could not find implicit value for parameter num: Numeric[String]
              names.sum
                    ^

scala> val interval = 1 to 10
interval: scala.collection.immutable.Range.Inclusive = Range(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)

scala> val interval = 1 until 10
interval: scala.collection.immutable.Range = Range(1, 2, 3, 4, 5, 6, 7, 8, 9)

scala> val interval = 1 until 10 toList
warning: there was one feature warning; re-run with -feature for details
interval: List[Int] = List(1, 2, 3, 4, 5, 6, 7, 8, 9)

scala> interval.map(n => (1 to n).toList)
res15: List[List[Int]] = List(List(1), List(1, 2), List(1, 2, 3), List(1, 2, 3, 4), List(1, 2, 3, 4, 5), List(1, 2, 3, 4, 5, 6), List(1, 2, 3, 4, 5, 6, 7), List(1, 2, 3, 4, 5, 6, 7, 8), List(1, 2, 3, 4, 5, 6, 7, 8, 9))

scala> interval.map(n => (1 to n).toList.map(k => (n, k)))
res16: List[List[(Int, Int)]] = List(List((1,1)), List((2,1), (2,2)), List((3,1), (3,2), (3,3)), List((4,1), (4,2), (4,3), (4,4)), List((5,1), (5,2), (5,3), (5,4), (5,5)), List((6,1), (6,2), (6,3), (6,4), (6,5), (6,6)), List((7,1), (7,2), (7,3), (7,4), (7,5), (7,6), (7,7)), List((8,1), (8,2), (8,3), (8,4), (8,5), (8,6), (8,7), (8,8)), List((9,1), (9,2), (9,3), (9,4), (9,5), (9,6), (9,7), (9,8), (9,9)))

scala> interval.map(n => (1 to n).toList.map(k => (n, k))).flatten
res17: List[(Int, Int)] = List((1,1), (2,1), (2,2), (3,1), (3,2), (3,3), (4,1), (4,2), (4,3), (4,4), (5,1), (5,2), (5,3), (5,4), (5,5), (6,1), (6,2), (6,3), (6,4), (6,5), (6,6), (7,1), (7,2), (7,3), (7,4), (7,5), (7,6), (7,7), (8,1), (8,2), (8,3), (8,4), (8,5), (8,6), (8,7), (8,8), (9,1), (9,2), (9,3), (9,4), (9,5), (9,6), (9,7), (9,8), (9,9))

scala> interval.flaMap(n => (1 to n).toList.map(k => (n, k)))
<console>:9: error: value flaMap is not a member of List[Int]
              interval.flaMap(n => (1 to n).toList.map(k => (n, k)))
                       ^

scala> interval.flatMap(n => (1 to n).toList.map(k => (n, k)))
res19: List[(Int, Int)] = List((1,1), (2,1), (2,2), (3,1), (3,2), (3,3), (4,1), (4,2), (4,3), (4,4), (5,1), (5,2), (5,3), (5,4), (5,5), (6,1), (6,2), (6,3), (6,4), (6,5), (6,6), (7,1), (7,2), (7,3), (7,4), (7,5), (7,6), (7,7), (8,1), (8,2), (8,3), (8,4), (8,5), (8,6), (8,7), (8,8), (9,1), (9,2), (9,3), (9,4), (9,5), (9,6), (9,7), (9,8), (9,9))

scala> interval
res20: List[Int] = List(1, 2, 3, 4, 5, 6, 7, 8, 9)

scala> def around(n: Int) = List(n -1 , n, n + 1)
around: (n: Int)List[Int]

scala> around(3)
res21: List[Int] = List(2, 3, 4)

scala> interval.map(around)
res22: List[List[Int]] = List(List(0, 1, 2), List(1, 2, 3), List(2, 3, 4), List(3, 4, 5), List(4, 5, 6), List(5, 6, 7), List(6, 7, 8), List(7, 8, 9), List(8, 9, 10))

scala> interval.flatMap(around)
res23: List[Int] = List(0, 1, 2, 1, 2, 3, 2, 3, 4, 3, 4, 5, 4, 5, 6, 5, 6, 7, 6, 7, 8, 7, 8, 9, 8, 9, 10)

scala> interval.map(_ * 2)
res24: List[Int] = List(2, 4, 6, 8, 10, 12, 14, 16, 18)

scala> interval.flatMap(x => List(x * 2))
res25: List[Int] = List(2, 4, 6, 8, 10, 12, 14, 16, 18)

scala> interval.first

<console>:9: error: value first is not a member of List[Int]
              interval.first
                       ^

scala> interval.first




<console>:9: error: value first is not a member of List[Int]
              interval.first
                       ^

scala> interval.head
res28: Int = 1

scala> interval = 1 to 10 tolist
<console>:8: error: reassignment to val
       interval = 1 to 10 tolist
                ^

scala> interval = 1 to 10 toList
<console>:8: error: reassignment to val
       interval = 1 to 10 toList
                ^

scala> val interval = 1 to 10 toList
warning: there was one feature warning; re-run with -feature for details
interval: List[Int] = List(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)

scala> interval.headOption
res29: Option[Int] = Some(1)

scala> List().headOption
res30: Option[Nothing] = None

scala> List().head
java.util.NoSuchElementException: head of empty list
  at scala.collection.immutable.Nil$.head(List.scala:420)
  at scala.collection.immutable.Nil$.head(List.scala:417)
  ... 35 elided

scala> 
val capitals = Map("France" -> "Paris", "Italy" -> "Rome", "Spain" -> "Madrid")
capitals: scala.collection.immutable.Map[String,String] = Map(France -> Paris, Italy -> Rome, Spain -> Madrid)

scala> capitals.get("France")
res32: Option[String] = Some(Paris)

scala> capitals.get("UK")
res33: Option[String] = None

scala> capitals.get("France").map(_.toUpperCase())
res34: Option[String] = Some(PARIS)

scala> capitals.get("UK").map(_.toUpperCase())
res35: Option[String] = None

scala> capitals.get("UK").map(_.length)
res36: Option[Int] = None

scala> capitals.get("France").map(_.length)
res37: Option[Int] = Some(5)

scala> val populations = Map("Paris" -> 15000000, "Rome" -> 4000000, "London" -> 10000000)
populations: scala.collection.immutable.Map[String,Int] = Map(Paris -> 15000000, Rome -> 4000000, London -> 10000000)

scala> populations("Paris")
res38: Int = 15000000

scala> populations("Madrid")
java.util.NoSuchElementException: key not found: Madrid
  at scala.collection.MapLike$class.default(MapLike.scala:228)
  at scala.collection.AbstractMap.default(Map.scala:59)
  at scala.collection.MapLike$class.apply(MapLike.scala:141)
  at scala.collection.AbstractMap.apply(Map.scala:59)
  ... 35 elided

scala> populations.get("Madrid")
res40: Option[Int] = None

scala> def getPopulationOfCapital(country: String): Option[Int] = {
  capitals.get(country).flatMap(capital => populations.get(capital))
}
     |      | getPopulationOfCapital: (country: String)Option[Int]

scala> getPopulationOfCapital("France")
res41: Option[Int] = Some(15000000)

scala> getPopulationOfCapital("UK")
res42: Option[Int] = None

scala> getPopulationOfCapital("Spain")
res43: Option[Int] = None

scala> def getPopulationOfCapital2(country: String): Option[Int] = {
  for {
    capital <- capitals.get(country)
    population <- populations.get(capital)
  } yield population
}
     |      |      |      |      | getPopulationOfCapital2: (country: String)Option[Int]

scala> def getPopulationOfCapital3(country: String): Option[String] = {
  for {
    capital <- capitals.get(country)
    population <- populations.get(capital)
  } yield s"The population of the capital of $country is $population"
}
     |      |      |      |      | getPopulationOfCapital3: (country: String)Option[String]

scala> getPopulationOfCapital3("France")
res44: Option[String] = Some(The population of the capital of France is 15000000)

scala> getPopulationOfCapital3("France") match {
  case Some(x) => x
  case None => "Not found"
}
     |      |      | res45: String = The population of the capital of France is 15000000

scala> val numbers = 1 to 4
numbers: scala.collection.immutable.Range.Inclusive = Range(1, 2, 3, 4)

scala> val numbers = 1 to 4.toList
<console>:7: error: value toList is not a member of Int
       val numbers = 1 to 4.toList
                            ^

scala> val numbers = 1 to 4 toList
warning: there was one feature warning; re-run with -feature for details
numbers: List[Int] = List(1, 2, 3, 4)

scala> for {
  i <- numbers
  j <- numbers.map(_ * 2)
} yield (i,j)
     |      |      | res46: List[(Int, Int)] = List((1,2), (1,4), (1,6), (1,8), (2,2), (2,4), (2,6), (2,8), (3,2), (3,4), (3,6), (3,8), (4,2), (4,4), (4,6), (4,8))

scala> :quit