x1. おまけ

Scala のメソッドは、

・引数が０個の場合は、メソッド名の後ろの ( ) を省略できる。

・オブジェクトとメソッドと引数を演算子の様に中間記法で表記できる。

・演算子をメソッド呼び出しの表記法で利用できる。（実は演算子はただのメソッド）

・メソッドの部分適用から関数オブジェクトを得ることが出来る。

scala> def a() = 123

a: ()Int

scala> a()

res0: Int = 123

scala> a

res1: Int = 123

scala> object o { def a()=234; def b(x:Int) = x}

defined object o

scala> o.a

res2: Int = 234

scala> o.b(345)

res3: Int = 345

scala> o b 345

res4: Int = 345

scala> o.b(_:Int)

res6: Int => Int = <function1>

scala> o.b(_:Int)(456)

<console>:9: error: Int does not take parameters

              o.b(_:Int)(456)

scala> (o.b(_:Int))(456)

res8: Int = 456

scala> object oo { def c(x:Int,y:Int) = x-y}

defined object oo

scala> oo.c(_:Int,_:Int)

res9: (Int, Int) => Int = <function2>

scala> oo.c(_:Int,_:Int).curried

<console>:9: error: value curried is not a member of Int

              oo.c(_:Int,_:Int).curried

scala> (oo.c(_:Int,_:Int)).curried

res11: Int => (Int => Int) = <function1>

scala> (oo.c(_:Int,_:Int)).curried 1 2

<console>:1: error: ';' expected but integer literal found.

       (oo.c(_:Int,_:Int)).curried 1 2

scala> (oo.c(_:Int,_:Int)).curried (1) (2)

res12: Int = -1

scala> object ooo { def c(x:Int)(y:Int) = x-y}

defined object ooo

scala> ooo.c (1)

<console>:9: error: missing arguments for method c in object ooo;

follow this method with `_' if you want to treat it as a partially applied function

              ooo.c (1)

scala> ooo.c (1) (2)

res15: Int = -1

scala> (ooo.c (1)) (2)

res16: Int = -1

scala> ooo.c(1) (_:Int)

res17: Int => Int = <function1>

scala> val aaa = ooo.c(1) (_:Int)

aaa: Int => Int = <function1>

scala> aaa (1)

res18: Int = 0

Stream

// 0 1 2 3 の遅延ストリーム

Stream.from(0)

val ls = List(1,2,3)

val ss = Stream(4,5,6)

scala> ls ::: ls

List[Int] = List(1, 2, 3, 1, 2, 3)

scala> ls.toStream #::: ss

res5: scala.collection.immutable.Stream[Int] = Stream(1, ?)

関数の引数の名前渡しで遅延評価

def f( a:Int , b: => Int)