search term:

# Scalaz cheat sheet

 ### Equal[A] ```scala def equal(a1: A, a2: A): Boolean (1 === 2) assert_=== false (2 =/= 1) assert_=== true ``` ### Order[A] ```scala def order(x: A, y: A): Ordering 1.0 ?|? 2.0 assert_=== Ordering.LT 1.0 lt 2.0 assert_=== true 1.0 gt 2.0 assert_=== false 1.0 lte 2.0 assert_=== true 1.0 gte 2.0 assert_=== false 1.0 max 2.0 assert_=== 2.0 1.0 min 2.0 assert_=== 1.0 ``` ### Show[A] ```scala def show(f: A): Cord 1.0.show assert_=== Cord("1.0") 1.0.shows assert_=== "1.0" 1.0.print assert_=== () 1.0.println assert_=== () ``` ### Enum[A] extends Order[A] ```scala def pred(a: A): A def succ(a: A): A 1.0 |-> 2.0 assert_=== List(1.0, 2.0) 1.0 |--> (2, 5) assert_=== List(1.0, 3.0, 5.0) // |=>/|==>/from/fromStep return EphemeralStream[A] (1.0 |=> 2.0).toList assert_=== List(1.0, 2.0) (1.0 |==> (2, 5)).toList assert_=== List(1.0, 3.0, 5.0) (1.0.from take 2).toList assert_=== List(1.0, 2.0) ((1.0 fromStep 2) take 2).toList assert_=== List(1.0, 3.0) 1.0.pred assert_=== 0.0 1.0.predx assert_=== Some(0.0) 1.0.succ assert_=== 2.0 1.0.succx assert_=== Some(2.0) 1.0 -+- 1 assert_=== 2.0 1.0 --- 1 assert_=== 0.0 Enum[Int].min assert_=== Some(-2147483648) Enum[Int].max assert_=== Some(2147483647) ``` ### Semigroup[A] ```scala def append(a1: A, a2: => A): A List(1, 2) |+| List(3) assert_=== List(1, 2, 3) List(1, 2) mappend List(3) assert_=== List(1, 2, 3) 1 |+| 2 assert_=== 3 (Tags.Multiplication(2) |+| Tags.Multiplication(3): Int) assert_=== 6 // Tags.Disjunction (||), Tags.Conjunction (&&) (Tags.Disjunction(true) |+| Tags.Disjunction(false): Boolean) assert_=== true (Tags.Conjunction(true) |+| Tags.Conjunction(false): Boolean) assert_=== false (Ordering.LT: Ordering) |+| (Ordering.GT: Ordering) assert_=== Ordering.LT (none: Option[String]) |+| "andy".some assert_=== "andy".some (Tags.First('a'.some) |+| Tags.First('b'.some): Option[Char]) assert_=== 'a'.some (Tags.Last('a'.some) |+| Tags.Last(none: Option[Char]): Option[Char]) assert_=== 'a'.some ``` ### Monoid[A] extends Semigroup[A] ```scala def zero: A mzero[List[Int]] assert_=== Nil ``` ### Functor[F[_]] ```scala def map[A, B](fa: F[A])(f: A => B): F[B] List(1, 2, 3) map {_ + 1} assert_=== List(2, 3, 4) List(1, 2, 3) ∘ {_ + 1} assert_=== List(2, 3, 4) List(1, 2, 3) >| "x" assert_=== List("x", "x", "x") List(1, 2, 3) as "x" assert_=== List("x", "x", "x") List(1, 2, 3).fpair assert_=== List((1,1), (2,2), (3,3)) List(1, 2, 3).strengthL("x") assert_=== List(("x",1), ("x",2), ("x",3)) List(1, 2, 3).strengthR("x") assert_=== List((1,"x"), (2,"x"), (3,"x")) List(1, 2, 3).void assert_=== List((), (), ()) Functor[List].lift {(_: Int) * 2} (List(1, 2, 3)) assert_=== List(2, 4, 6) ``` ### Pointed[F[_]] extends Functor[F] ```scala def point[A](a: => A): F[A] 1.point[List] assert_=== List(1) 1.η[List] assert_=== List(1) ``` ### Apply[F[_]] extends Functor[F] ```scala def ap[A,B](fa: => F[A])(f: => F[A => B]): F[B] 1.some <*> {(_: Int) + 2}.some assert_=== Some(3) // except in 7.0.0-M3 1.some <*> { 2.some <*> {(_: Int) + (_: Int)}.curried.some } assert_=== 3.some 1.some <* 2.some assert_=== 1.some 1.some *> 2.some assert_=== 2.some Apply[Option].ap(9.some) {{(_: Int) + 3}.some} assert_=== 12.some Apply[List].lift2 {(_: Int) * (_: Int)} (List(1, 2), List(3, 4)) assert_=== List(3, 4, 6, 8) (3.some |@| 5.some) {_ + _} assert_=== 8.some // ^(3.some, 5.some) {_ + _} assert_=== 8.some ``` ### Applicative[F[_]] extends Apply[F] with Pointed[F] ```scala // no contract function ``` ### Product/Composition ```scala (Applicative[Option] product Applicative[List]).point(0) assert_=== (0.some, List(0)) (Applicative[Option] compose Applicative[List]).point(0) assert_=== List(0).some ``` ### Bind[F[_]] extends Apply[F] ```scala def bind[A, B](fa: F[A])(f: A => F[B]): F[B] 3.some flatMap { x => (x + 1).some } assert_=== 4.some (3.some >>= { x => (x + 1).some }) assert_=== 4.some 3.some >> 4.some assert_=== 4.some List(List(1, 2), List(3, 4)).join assert_=== List(1, 2, 3, 4) ``` ### Monad[F[_]] extends Applicative[F] with Bind[F] ```scala // no contract function // failed pattern matching produces None (for {(x :: xs) <- "".toList.some} yield x) assert_=== none (for { n <- List(1, 2); ch <- List('a', 'b') } yield (n, ch)) assert_=== List((1, 'a'), (1, 'b'), (2, 'a'), (2, 'b')) (for { a <- (_: Int) * 2; b <- (_: Int) + 10 } yield a + b)(3) assert_=== 19 List(1, 2) filterM { x => List(true, false) } assert_=== List(List(1, 2), List(1), List(2), List()) ``` ### Plus[F[_]] ```scala def plus[A](a: F[A], b: => F[A]): F[A] List(1, 2) <+> List(3, 4) assert_=== List(1, 2, 3, 4) ``` ### PlusEmpty[F[_]] extends Plus[F] ```scala def empty[A]: F[A] (PlusEmpty[List].empty: List[Int]) assert_=== Nil ``` ### ApplicativePlus[F[_]] extends Applicative[F] with PlusEmpty[F] ```scala // no contract function ``` ### MonadPlus[F[_]] extends Monad[F] with ApplicativePlus[F] ```scala // no contract function List(1, 2, 3) filter {_ > 2} assert_=== List(3) ``` ### Foldable[F[_]] ```scala def foldMap[A,B](fa: F[A])(f: A => B)(implicit F: Monoid[B]): B def foldRight[A, B](fa: F[A], z: => B)(f: (A, => B) => B): B List(1, 2, 3).foldRight (0) {_ + _} assert_=== 6 List(1, 2, 3).foldLeft (0) {_ + _} assert_=== 6 (List(1, 2, 3) foldMap {Tags.Multiplication}: Int) assert_=== 6 List(1, 2, 3).foldLeftM(0) { (acc, x) => (acc + x).some } assert_=== 6.some ``` ### Traverse[F[_]] extends Functor[F] with Foldable[F] ```scala def traverseImpl[G[_]:Applicative,A,B](fa: F[A])(f: A => G[B]): G[F[B]] List(1, 2, 3) traverse { x => (x > 0) option (x + 1) } assert_=== List(2, 3, 4).some List(1, 2, 3) traverseU {_ + 1} assert_=== 9 List(1.some, 2.some).sequence assert_=== List(1, 2).some 1.success[String].leaf.sequenceU map {_.drawTree} assert_=== "1\n".success[String] ``` ### Length[F[_]] ```scala def length[A](fa: F[A]): Int List(1, 2, 3).length assert_=== 3 ``` ### Index[F[_]] ```scala def index[A](fa: F[A], i: Int): Option[A] List(1, 2, 3) index 2 assert_=== 3.some List(1, 2, 3) index 3 assert_=== none ``` ### ArrId[=>:[_, _]] ```scala def id[A]: A =>: A ``` ### Compose[=>:[_, _]] ```scala def compose[A, B, C](f: B =>: C, g: A =>: B): (A =>: C) val f1 = (_:Int) + 1 val f2 = (_:Int) * 100 (f1 >>> f2)(2) assert_=== 300 (f1 <<< f2)(2) assert_=== 201 ``` ### Category[=>:[_, _]] extends ArrId[=>:] with Compose[=>:] ```scala // no contract function ``` ### Arrow[=>:[_, _]] extends Category[=>:] ```scala def arr[A, B](f: A => B): A =>: B def first[A, B, C](f: (A =>: B)): ((A, C) =>: (B, C)) val f1 = (_:Int) + 1 val f2 = (_:Int) * 100 (f1 *** f2)(1, 2) assert_=== (2, 200) (f1 &&& f2)(1) assert_=== (2,100) ``` ### Unapply[TC[`_`[`_`]], MA] ```scala type M[_] type A def TC: TC[M] def apply(ma: MA): M[A] implicitly[Unapply[Applicative, Int => Int]].TC.point(0).asInstanceOf[Int => Int](10) assert_=== Applicative[({type l[x]=Function1[Int, x]})#l].point(0)(10) List(1, 2, 3) traverseU {(x: Int) => {(_:Int) + x}} apply 1 assert_=== List(2, 3, 4) // traverse won't work ``` ### Boolean ```scala false /\ true assert_=== false // && false \/ true assert_=== true // || (1 < 10) option 1 assert_=== 1.some (1 > 10)? 1 | 2 assert_=== 2 (1 > 10)?? {List(1)} assert_=== Nil ``` ### Option ```scala 1.some assert_=== Some(1) none[Int] assert_=== (None: Option[Int]) 1.some? 'x' | 'y' assert_=== 'x' 1.some | 2 assert_=== 1 // getOrElse ``` ### Id[+A] = A ```scala // no contract function 1 + 2 + 3 |> {_ * 6} 1 visit { case x@(2|3) => List(x * 2) } ``` ### Tagged[A] ```scala sealed trait KiloGram def KiloGram[A](a: A): A @@ KiloGram = Tag[A, KiloGram](a) def f[A](mass: A @@ KiloGram): A @@ KiloGram ``` ### Tree[A]/TreeLoc[A] ```scala val tree = 'A'.node('B'.leaf, 'C'.node('D'.leaf), 'E'.leaf) (tree.loc.getChild(2) >>= {_.getChild(1)} >>= {_.getLabel.some}) assert_=== 'D'.some (tree.loc.getChild(2) map {_.modifyLabel({_ => 'Z'})}).get.toTree.drawTree assert_=== 'A'.node('B'.leaf, 'Z'.node('D'.leaf), 'E'.leaf).drawTree ``` ### Stream[A]/Zipper[A] ```scala (Stream(1, 2, 3, 4).toZipper >>= {_.next} >>= {_.focus.some}) assert_=== 2.some (Stream(1, 2, 3, 4).zipperEnd >>= {_.previous} >>= {_.focus.some}) assert_=== 3.some (for { z <- Stream(1, 2, 3, 4).toZipper; n1 <- z.next } yield { n1.modify {_ => 7} }) map { _.toStream.toList } getOrElse Nil assert_=== List(1, 7, 3, 4) unfold(3) { x => (x =/= 0) option (x, x - 1) }.toList assert_=== List(3, 2, 1) ``` ### DList[A] ```scala DList.unfoldr(3, { (x: Int) => (x =/= 0) option (x, x - 1) }).toList assert_=== List(3, 2, 1) ``` ### Lens[A, B] = LensT[Id, A, B] ```scala val t0 = Turtle(Point(0.0, 0.0), 0.0) val t1 = Turtle(Point(1.0, 0.0), 0.0) val turtlePosition = Lens.lensu[Turtle, Point] ( (a, value) => a.copy(position = value), _.position) val pointX = Lens.lensu[Point, Double] ( (a, value) => a.copy(x = value), _.x) val turtleX = turtlePosition >=> pointX turtleX.get(t0) assert_=== 0.0 turtleX.set(t0, 5.0) assert_=== Turtle(Point(5.0, 0.0), 0.0) turtleX.mod(_ + 1.0, t0) assert_=== t1 t0 |> (turtleX =>= {_ + 1.0}) assert_=== t1 (for { x <- turtleX %= {_ + 1.0} } yield x) exec t0 assert_=== t1 (for { x <- turtleX := 5.0 } yield x) exec t0 assert_=== Turtle(Point(5.0, 0.0), 0.0) (for { x <- turtleX += 1.0 } yield x) exec t0 assert_=== t1 ``` ### Validation[+E, +A] ```scala (1.success[String] |@| "boom".failure[Int] |@| "boom".failure[Int]) {_ |+| _ |+| _} assert_=== "boomboom".failure[Int] (1.successNel[String] |@| "boom".failureNel[Int] |@| "boom".failureNel[Int]) {_ |+| _ |+| _} assert_=== NonEmptyList("boom", "boom").failure[Int] "1".parseInt.toOption assert_=== 1.some ``` ### Writer[+W, +A] = WriterT[Id, W, A] ```scala (for { x <- 1.set("log1"); _ <- "log2".tell } yield (x)).run assert_=== ("log1log2", 1) import std.vector._ MonadWriter[Writer, Vector[String]].point(1).run assert_=== (Vector(), 1) ``` ### \/[+A, +B] ```scala 1.right[String].isRight assert_=== true 1.right[String].isLeft assert_=== false 1.right[String] | 0 assert_=== 1 // getOrElse ("boom".left ||| 2.right) assert_=== 2.right // orElse ("boom".left[Int] >>= { x => (x + 1).right }) assert_=== "boom".left[Int] (for { e1 <- 1.right; e2 <- "boom".left[Int] } yield (e1 |+| e2)) assert_=== "boom".left[Int] ``` ### Kleisli[M[+_], -A, +B] ```scala val k1 = Kleisli { (x: Int) => (x + 1).some } val k2 = Kleisli { (x: Int) => (x * 100).some } (4.some >>= k1 compose k2) assert_=== 401.some (4.some >>= k1 <=< k2) assert_=== 401.some (4.some >>= k1 andThen k2) assert_=== 500.some (4.some >>= k1 >=> k2) assert_=== 500.some ``` ### Reader[E, A] = Kleisli[Id, E, A] ```scala Reader { (_: Int) + 1 } ``` ### trait Memo[K, V] ```scala val memoizedFib: Int => Int = Memo.mutableHashMapMemo { case 0 => 0 case 1 => 1 case n => memoizedFib(n - 2) + memoizedFib(n - 1) } ``` ### State[S, +A] = StateT[Id, S, A] ```scala State[List[Int], Int] { case x :: xs => (xs, x) }.run(1 :: Nil) assert_=== (Nil, 1) (for { xs <- get[List[Int]] _ <- put(xs.tail) } yield xs.head).run(1 :: Nil) assert_=== (Nil, 1) ``` ### ST[S, A]/STRef[S, A]/STArray[S, A] ```scala import scalaz._, Scalaz._, effect._, ST._ type ForallST[A] = Forall[({type l[x] = ST[x, A]})#l] def e1[S]: ST[S, Int] = for { x <- newVar[S](0) _ <- x mod {_ + 1} r <- x.read } yield r runST(new ForallST[Int] { def apply[S] = e1[S] }) assert_=== 1 def e2[S]: ST[S, ImmutableArray[Boolean]] = for { arr <- newArr[S, Boolean](3, true) x <- arr.read(0) _ <- arr.write(0, !x) r <- arr.freeze } yield r runST(new ForallST[ImmutableArray[Boolean]] { def apply[S] = e2[S] })(0) assert_=== false ``` ### IO[+A] ```scala import scalaz._, Scalaz._, effect._, IO._ val action1 = for { x <- readLn _ <- putStrLn("Hello, " + x + "!") } yield () action1.unsafePerformIO ``` ### IterateeT[E, F[`_`], A]/EnumeratorT[O, I, F[`_`]] ```scala import scalaz._, Scalaz._, iteratee._, Iteratee._ (length[Int, Id] &= enumerate(Stream(1, 2, 3))).run assert_=== 3 (length[scalaz.effect.IoExceptionOr[Char], IO] &= enumReader[IO](new BufferedReader(new FileReader("./README.md")))).run.unsafePerformIO ``` ### Free[S[+`_`], +A] ```scala import scalaz._, Scalaz._, Free._ type FreeMonoid[A] = Free[({type λ[+α] = (A,α)})#λ, Unit] def cons[A](a: A): FreeMonoid[A] = Suspend[({type λ[+α] = (A,α)})#λ, Unit]((a, Return[({type λ[+α] = (A,α)})#λ, Unit](()))) def toList[A](list: FreeMonoid[A]): List[A] = list.resume.fold( { case (x: A, xs: FreeMonoid[A]) => x :: toList(xs) }, { _ => Nil }) toList(cons(1) >>= {_ => cons(2)}) assert_=== List(1, 2) ``` ### Trampoline[+A] = Free[Function0, A] ```scala import scalaz._, Scalaz._, Free._ def even[A](ns: List[A]): Trampoline[Boolean] = ns match { case Nil => return_(true) case x :: xs => suspend(odd(xs)) } def odd[A](ns: List[A]): Trampoline[Boolean] = ns match { case Nil => return_(false) case x :: xs => suspend(even(xs)) } even(0 |-> 3000).run assert_=== false ``` ### Imports ```scala import scalaz._ // imports type names import scalaz.Id.Id // imports Id type alias import scalaz.std.option._ // imports instances, converters, and functions related to `Option` import scalaz.std.AllInstances._ // imports instances and converters related to standard types import scalaz.std.AllFunctions._ // imports functions related to standard types import scalaz.syntax.monad._ // injects operators to Monad import scalaz.syntax.all._ // injects operators to all typeclasses and Scalaz data types import scalaz.syntax.std.boolean._ // injects operators to Boolean import scalaz.syntax.std.all._ // injects operators to all standard types import scalaz._, Scalaz._ // all the above ``` ### Note ```scala type Function1Int[A] = ({type l[x]=Function1[Int, x]})#l[A] type Function1Int[A] = Function1[Int, A] ```