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➜ ~ scala
Welcome to Scala version 2.11.6 (OpenJDK 64-Bit Server VM, Java 1.7.0_75).
Type in expressions to have them evaluated.
Type :help for more information.
scala> def partial1[A,B,C](a: A, f: (A,B) => C): B => C =
| (b: B) => f(a, b)
partial1: [A, B, C](a: A, f: (A, B) => C)B => C
scala> partial1(3, (x: Int, y: Int => x + y)(3)
| )
<console>:9: error: not found: value x
partial1(3, (x: Int, y: Int => x + y)(3)
^
<console>:9: error: not found: type +
partial1(3, (x: Int, y: Int => x + y)(3)
^
<console>:9: error: not found: value y
partial1(3, (x: Int, y: Int => x + y)(3)
^
scala> partial1(3, (x: Int, y: Int => x + y))(3)
<console>:9: error: not found: value x [847/870]
partial1(3, (x: Int, y: Int => x + y))(3)
^
<console>:9: error: not found: type +
partial1(3, (x: Int, y: Int => x + y))(3)
^
<console>:9: error: not found: value y
partial1(3, (x: Int, y: Int => x + y))(3)
^
scala> partial1(3, (x: Int, y: Int) => x + y)(3)
res2: Int = 6
scala> def curry[A,B,C](f: (A, B) => C): A => (B => C) =
| a => b => f(a, b)
curry: [A, B, C](f: (A, B) => C)A => (B => C)
scala>
scala> curry(3, (x: Int, y: Int) => x + y)(3)
<console>:9: error: too many arguments for method curry: (f: (A, B) => C)A => (B => C)
curry(3, (x: Int, y: Int) => x + y)(3)
^
scala> curry((x: Int, y: Int) => x + y)(2)(3) [823/870]
res4: Int = 5
scala> curry((x: Int, y: Int) => x + y)(2)(3)
scala> curry((x: Int, y: Int) => x + y)(2)(3)
res5: Int = 5
scala> curry((x: Int, y: Int) => x + y)(2)(3)
res6: Int = 5
scala> curry((x: Int, y: Int) => x + y)(4)(19)
res7: Int = 23
scala> def uncurry[A,B,C](f: A => B => C): (A, B) => C =
| (a, b) => f(a)(b)
uncurry: [A, B, C](f: A => (B => C))(A, B) => C
scala>
scala> curry((x: Int, y: Int) => x + y)(4, 19)
<console>:9: error: too many arguments for method apply: (v1: Int)Int => Int in trait Function1
curry((x: Int, y: Int) => x + y)(4, 19)
scala> uncurry((x: Int, y: Int) => x + y)(4, 19) [798/870]
<console>:9: error: type mismatch;
found : (Int, Int) => Int
required: ? => (? => ?)
uncurry((x: Int, y: Int) => x + y)(4, 19)
^
scala> uncurry(x: Int => y: Int => x + y)(2, 3)
<console>:1: error: ')' expected but ':' found.
uncurry(x: Int => y: Int => x + y)(2, 3)
^
scala> uncurry((x: Int) => (y: Int) => x + y)(2, 3)
res10: Int = 5
scala> uncurry((x: Int) => (y: Int) => x + y)(4, 3)
res11: Int = 7
scala> def compose[A,B,C](f: B => C, g: A => B): A => C =
| a => f(g(a))
compose: [A, B, C](f: B => C, g: A => B)A => C
scala>
scala> def compose[A,B,C](f: B => C, g: A => B): A => C = [774/870]
| a => f(g(a))
compose: [A, B, C](f: B => C, g: A => B)A => C
scala> compose((x: Int) => x + 2, (y: Int) => y * 2)(3)
res12: Int = 8
scala> uncurry((x: Int) => (y: Int) => x + y)(4, 3)
res13: Int = 7
scala> curry((x: Int, y: Int) => x + y)(4, 19)
<console>:9: error: too many arguments for method apply: (v1: Int)Int => Int in trait Function1
curry((x: Int, y: Int) => x + y)(4, 19)
^
scala> curry((x: Int, y: Int) => x + y)(4)(19)
res15: Int = 23
scala> val f (x: Double) => math.Pi / 2 -x
<console>:1: error: '=' expected but '=>' found.
val f (x: Double) => math.Pi / 2 -x
^
scala> val f (x: Double) => math.Pi / 2 - x [751/870]
<console>:1: error: '=' expected but '=>' found.
val f (x: Double) => math.Pi / 2 - x
^
scala> val f = (x: Double) => math.Pi / 2 - x
f: Double => Double = <function1>
scala> f andThen math.sin
res16: Double => Double = <function1>
scala> def f(x: Double) => math.Pi / 2 - x
<console>:1: error: '=' expected but '=>' found.
def f(x: Double) => math.Pi / 2 - x
^
scala> def f(x: Double): Double => math.Pi / 2 - x
<console>:1: error: identifier expected but integer literal found.
def f(x: Double): Double => math.Pi / 2 - x
^
scala> def f(x: Double): Double = math.Pi / 2 - x
f: (x: Double)Double
scala> f(2) [727/870]
res17: Double = -0.42920367320510344
scala> f andThen math.sin
<console>:9: error: missing arguments for method f;
follow this method with `_' if you want to treat it as a partially applied function
f andThen math.sin
^
<console>:9: error: missing arguments for method sin in package math;
follow this method with `_' if you want to treat it as a partially applied function
f andThen math.sin
^
scala> f _ andThen math.sin
res19: Double => Double = <function1>
scala> f 2 andThen math.sin
<console>:1: error: ';' expected but integer literal found.
f 2 andThen math.sin
^
scala> f _ andThen math.sin
res20: Double => Double = <function1>
scala> f _ [703/870]
res21: Double => Double = <function1>
scala> f
<console>:9: error: missing arguments for method f;
follow this method with `_' if you want to treat it as a partially applied function
f
^
scala> f 2
<console>:1: error: ';' expected but integer literal found.
f 2
^
scala> f(2)
res23: Double = -0.42920367320510344
scala> f _
res24: Double => Double = <function1>
scala> val g = f _
g: Double => Double = <function1>
scala> g(2) [680/870]
res25: Double = -0.42920367320510344
scala>
scala> f _ andThen math.sin
res26: Double => Double = <function1>
scala> val g = f _ andThen math.sin
g: Double => Double = <function1>
scala> g(2)
res27: Double = -0.41614683654714246
scala> val g = f andThen math.sin
<console>:8: error: missing arguments for method f;
follow this method with `_' if you want to treat it as a partially applied function
val g = f andThen math.sin
^
<console>:8: error: missing arguments for method sin in package math;
follow this method with `_' if you want to treat it as a partially applied function
val g = f andThen math.sin
^
scala> val g = f _ andThen math.sin [656/870]
g: Double => Double = <function1>
scala> def f(x: Double): Double = math.Pi / 2 - x
f: (x: Double)Double
scala> val g = f _ andThen math.sin
g: Double => Double = <function1>
scala> g(2)
res28: Double = -0.41614683654714246
scala>
scala>
scala> object List { // `List` companion object. Contains functions for creating and working with lists.
| def sum(ints: List[Int]): Int = ints match { // A function that uses pattern matching to add up a list of
integers
| case Nil => 0 // The sum of the empty list is 0.
| case Cons(x,xs) => x + sum(xs) // The sum of a list starting with `x` is `x` plus the sum of the rest of
the list.
| }
| [633/870]
| def product(ds: List[Double]): Double = ds match {
| case Nil => 1.0
| case Cons(0.0, _) => 0.0
| case Cons(x,xs) => x * product(xs)
| }
|
| def apply[A](as: A*): List[A] = // Variadic function syntax
| if (as.isEmpty) Nil
| else Cons(as.head, apply(as.tail: _*))
| }
<console>:10: error: not found: value Cons
case Cons(x,xs) => x + sum(xs) // The sum of a list starting with `x` is `x` plus the sum of the rest of
the list.
^
<console>:15: error: not found: value Cons
case Cons(0.0, _) => 0.0
^
<console>:16: error: not found: value Cons
case Cons(x,xs) => x * product(xs)
^
<console>:21: error: not found: value Cons
else Cons(as.head, apply(as.tail: _*))
scala> sealed trait List[+A] // `List` data type, parameterized on a type, `A` [608/870]
defined trait List
scala> case object Nil extends List[Nothing] // A `List` data constructor representing the empty list
defined object Nil
scala> case class Cons[+A](head: A, tail: List[A]) extends List[A] // Another data constructor, representing nonemp
ty lists. Note that `tail` is another `List[A]`, which may be `Nil` or another `Cons`.
defined class Cons
scala> object List { // `List` companion object. Contains functions for creating and working with lists.
| def sum(ints: List[Int]): Int = ints match { // A function that uses pattern matching to add up a list of
integers
| case Nil => 0 // The sum of the empty list is 0.
| case Cons(x,xs) => x + sum(xs) // The sum of a list starting with `x` is `x` plus the sum of the rest of
the list.
| }
|
| def product(ds: List[Double]): Double = ds match {
| case Nil => 1.0
| case Cons(0.0, _) => 0.0
| case Cons(x,xs) => x * product(xs)
| }
| [585/870]
| def apply[A](as: A*): List[A] = // Variadic function syntax
| if (as.isEmpty) Nil
| else Cons(as.head, apply(as.tail: _*))
|
| }
defined object List
warning: previously defined trait List is not a companion to object List.
Companions must be defined together; you may wish to use :paste mode for this.
scala> List.sum((1,2,3,4,5))
<console>:13: error: type mismatch;
found : (Int, Int, Int, Int, Int)
required: List[Int]
List.sum((1,2,3,4,5))
^
scala> List.sum(List(1,2,3,4,5))
res30: Int = 15
scala> List.product(List(1,2,3,4,5))
res31: Double = 120.0
scala> List(List(1,2,3,4,5)) [562/870]
res32: List[List[Int]] = Cons(Cons(1,Cons(2,Cons(3,Cons(4,Cons(5,Nil))))),Nil)
scala> val ex1: List
scala> val ex1: List[Double] = Nil
ex1: List[Double] = Nil
scala> val ex2: List[Int] = Cons(1, Nil)
ex2: List[Int] = Cons(1,Nil)
scala> val ex3: List[String] = Cons("a", Cons("b", Nil))
ex3: List[String] = Cons(a,Cons(b,Nil))
scala> val ex1: List[Double] = Nil
ex1: List[Double] = Nil
scala> :quit
➜ ~ scala
Welcome to Scala version 2.11.6 (OpenJDK 64-Bit Server VM, Java 1.7.0_75).
Type in expressions to have them evaluated.
Type :help for more information.
scala> sealed trait List[A] [539/870]
defined trait List
scala> case object Nil extends List[Nothing]
defined object Nil
scala> case class Cons[+A](head: A, tail: List[A]) extends List[A]
<console>:8: error: covariant type A occurs in invariant position in type [+A]AnyRef
with List[A]
with Product
with Serializable {
val head: A
private[this] val head: A
val tail: List[A]
private[this] val tail: List[A]
def <init>(head: A,tail: List[A]): Cons[A]
def copy[A](head: A,tail: List[A]): Cons[A]
def copy$default$1[A]: A @scala.annotation.unchecked.uncheckedVariance
def copy$default$2[A]: List[A] @scala.annotation.unchecked.uncheckedVariance
override def productPrefix: String
def productArity: Int
def productElement(x$1: Int): Any
override def productIterator: Iterator[Any]
def canEqual(x$1: Any): Boolean [516/870]
override def hashCode(): Int
override def toString(): String
override def equals(x$1: Any): Boolean
} of class Cons
case class Cons[+A](head: A, tail: List[A]) extends List[A]
^
<console>:8: error: covariant type A occurs in invariant position in type => List[A] of value tail
case class Cons[+A](head: A, tail: List[A]) extends List[A]
^
scala> case class Cons[A](head: A, tail: List[A]) extends List[A]
defined class Cons
scala> val ex1: List[Int] = Nil
<console>:9: error: type mismatch;
found : Nil.type
required: List[Int]
Note: Nothing <: Int (and Nil.type <: List[Nothing]), but trait List is invariant in type A.
You may wish to define A as +A instead. (SLS 4.5)
val ex1: List[Int] = Nil
^
scala> case object Nil[A] extends List[A]
<console>:1: error: ';' expected but '[' found.
case object Nil[A] extends List[A]
^
scala> case object Nil(A) extends List[A]
<console>:1: error: traits or objects may not have parameters
case object Nil(A) extends List[A]
^
scala> case object Nil(A) extends List[A]%
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