学生向けScalaハンズオンテキスト - プログラミング言語「Scala」 - Scalaの基本文法 - 平均値を表示するCLIツールを作ってみよう

1. Scala

2. Scala

3. Scala JVM

4. JVM

5. OS

6. VM OS
VM
1

8. Scala

11. Scala

12. Scala

13. // 1
/*
*
*/
println("Hello, world!") //

16. 42 // Int
3.14 // Double
"hogehoge" // String
true // Boolean
() // Unit

17. Array(1, 2, 3) //
List(1, 2, 3) //
Map("a" -> 1, "b" -> 2) //
Set(1, 2, 3) //

18. 1 :: 2 :: 3 :: Nil
// :: Nil
// List(1, 2, 3)

19. (42, "string", 3.14) //
s"$value ${value2}" // $ ${}

21. val i = 42 // val
// i = 99 // val
val j: Int = 100 //
// k: String = 100 //
var x = 42 //
x = 99 //

23. Scala if for match while

25. // if (cond) cond Boolean
if (cond) {
...
} else {
...
}

26. for (i <- seq) {
...
}

28. // Scala if for
val ret = if (false) {
"aaa"
} else if (true) {
"bbb"
} else {
"ccc"
}
ret // => "bbb"

29. val list = 1 :: 2 :: 3 :: Nil
val ret = for (i <- list) { i * 2 }
ret //=> Unit
// for
// list.foreach { i => ... }
val list = for (i <- list) yield { i * 2 }
list //=> List(2, 4, 6)
// yield yield
// list.map { i => ... }

30. val num = 42
// match
num match {
case n if n > 40 => println("over 40.")
case _ => println("less than or equal to 40.") // _
}

32. val tuple = (42, "answer")
val (i, s) = tuple
i // 42
s // tuple
// match
tuple match {
case (40, s) => println(s"40 is $s")
case (i, "universe") => println(s"$i is universe")
case (i, s) => println(s"$i is $s")
}

33. val tuple = (42, "hogefuga", 3.14)
tuple match {
case (40, "foobar", 2.718) => //
case (Num, Str, Point) => //
case (`num`, `str`, `p`) => //
case (n: Int, s: String, p: Int) => //
case tup @ (n, s, p) => //
}

34. val list = 1 :: 2 :: 3 :: Nil
// head tail
val head :: tail = list
head // 1
tail // List(2, 3)
list match {
case 42 :: tail => // 42
case head :: Nil => // Nil 1
case e1 :: e2 :: _ => // 2
case Nil => //
}

35. //
val tuple = (42, "answer", 1 :: 2 :: 3 :: Nil)
tuple match {
case (40, str, head :: Nil) =>
case (i, "answer", x :: xs) =>
case (_, _, list @ (head :: tail)) => // list List
case _ => //
}

37. Scala
def

38. def func(x: Int, y: Int): Int = {
x + y
}
//
// 1
def func2(x: Int, y: Int) = x + y

39. Scala

40. //
val fun = (x: Int, y: Int) => x + y
//
fun(1, 2) //=> 3

41. =>

43. // x y Int
val fun: (Int, Int) => Int = (x, y) => x + y

44. =>

45. match =>
=>

46. // =>
val fun: Int => String = (i: Int) => i match {
case 42 => "correct"
}

48. val fun = (x: Int, y: Int) = x + y
//
def fortytwo(num: Int, f: (Int, Int) => Int) = f(num, 42)
//
fortytwo(99, fun) // 141
//
fortytwo(2, (x, y) => x * y) // 84
// fortytwo x y

49. map

51. map
map

52. Scala List map

53. val list = 1 :: 2 :: 3 :: Nil
// 2
val fun = i: Int => i * 2
// map
list.map(fun) //=> List(2, 4, 6)
// List fun
//
list.map(i => i + 2) // List(3, 4, 5)

54. CLI

56. $ scala cli.scala 74 76 81 89 92 87 79 85
mean: 82

59. object Main {
def main(args: Array[String]): Unit = {
println("Hello, world!")
}
}

60. cli.scala
Hello, world!
$ scala cli.scala

61. Scala

62. sbt

63. Scala sbt

64. sbt
$ sbt

65. compile
run main

66. sbt
sbt target

67. 1-1

70. Scala main

71. object Main {
def main(args: Array[String]): Unit = {
for (arg <- args) {
println(arg)
}
}
}

72. args.scala

73. $ scala args.scala hoge fuga
hoge
fuga
$ scala args.scala 42 99
42
99

75. 2-1

77. Scala 2.11 scala.io.StdIn

78. object Main {
def main(args: Array[String]): Unit = {
val input = scala.io.StdIn.readLine
println(input)
}
}

79. stdin.scala

80. $ scala stdin.scala

82. $ scala stdin.scala
Hello, world!
Hello, world!

84. split

85. object Main {
def main(args: Array[String]): Unit = {
val input = scala.io.StdIn.readLine.split(" ")
for (word <- input) println(word)
}
}

87. $ scala stdin.scala
hoge fuga piyo
hoge
fuga
piyo

88. 2-2

90. Scala
……

91. 42 + "99" // toString "4299"

92. Ruby JavaScript

93. Ruby
irb(main):001:0> 42 + "99"
TypeError: String can't be coerced into Fixnum
from (irb):1:in `+'
from (irb):1

94. JavaScript
> 42 + '99'
'4299'
> '7' * 9
63
> 42 * 'hoge'
NaN

95. Scala
NaN

96. Scala
implicit

97. toInt
toDouble

98. 42 + "99".toInt // 141
3 * 3 * "3.14".toDouble // 28.26

99. 2

100. object Main {
def main(args: Array[String]): Unit = {
for (arg <- args) {
println(arg.toInt * 2)
}
}
}

101. number.scala
$ scala number.scala 42 99 1
84
198
2

103. 3-1
"hoge" toInt
toDouble

104. Array[String] ->
List[Double]

105. Array
Array List
toDouble

106. toList
Array toList List

107. args.toList

108. map
map

109. map
Double

110. args.map(_.toDouble)

112. Array[String] List[Double]
args.map(_.toDouble).toList

113. 4-1
Array[String] List[Double]

114. Array List
val arr = Array("1", "2", "3")
val list = List(1.0, 2.0, 3.0)

116. CLI
/

118. sum

119. sum
Scala sum

121. sum

123. 0

124. Scala Nil
Nil sum(Nil) 0

125. 1 2
3 ……
n
n

126. n n n-1
n = 1 n-1

127. n n
1..n
1..n 1..n-1 n

128. 1 + 2 + ... + n - 2 + n - 1 + n = (1 +
2 + ... n - 2 + n - 1) + n

129. 3 :: 2 :: 7 :: 5 :: Nil
1 4 17 1 3
12 4 5
17

130. n
1

131. n - 1 = 0 0
n - 1 > 0

132. 0
0

133. sum

134. 0
n n 1..n-1

135. Scala

136. sum( 3 :: 2 :: 7 :: 5 :: Nil )
3 + sum( 2 :: 7 :: 5 :: Nil )
3 + 2 + sum( 7 :: 5 :: Nil)
3 + 2 + 7 + sum( 5 :: Nil)
3 + 2 + 7 + 5 + sum( Nil )
3 + 2 + 7 + 5 + 0
3 + 2 + 7 + 5
3 + 2 + 12
3 + 14
17

137. Scala

138. Scala

139. def sum(list: List[Double]): Double = ???

140. List[Double]
Double

142. if
match

143. def sum(list: List[Double]): Double =
list match {
case Nil => ???
case head :: tail => ???
}

144. 0

145. def sum(list: List[Double]): Double =
list match {
case Nil => 0
case head :: tail => ???
}

147. def sum(list: List[Double]): Double =
list match {
case Nil => 0
case head :: tail => head + sum(tail)
}

149. 5-1

150. 1 :: 2 :: 3 :: Nil match {
case a :: b :: rest =>
println(a) // 1
println(b) // 2
println(rest) // List(3)
}

151. 1

152. length

153. sum
length

154. sum 0
length

155. sum
0

156. n
n n-1

157. 1 1
n-1 1 n

158. n
n-1

159. sum 3 :: 2 :: 7
:: 5 :: Nil

160. length( 3 :: 2 :: 7 :: 5 :: Nil )
1 + length( 2 :: 7 :: 5 :: Nil )
1 + 1 + length( 7 :: 5 :: Nil )
1 + 1 + 1 + length( 5 :: Nil )
1 + 1 + 1 + 1 + length( Nil )
1 + 1 + 1 + 1 + 0
1 + 1 + 1 + 1
1 + 1 + 2
1 + 3
4

161. Scala

162. def length(list: List[Double]): Double =
list match {
case Nil => 0
case _ :: tail => 1 + length(tail)
}

163. _ Scala

164. _

165. 6-1
_

166. _

167. mean

168. /

170. def mean(list: List[Double]): Double = sum(list) / length(list)

172. CLI

173. CLI

174. object Main {
def sum(list: List[Double]): Double =
list match {
case Nil => 0
case head :: tail => head + sum(tail)
}
def length(list: List[Double]): Double =
list match {
case Nil => 0
case _ :: tail => 1 + length(tail)
}
def mean(list: List[Double]): Double = sum(list) / length(list)
def main(args: Array[String]): Unit = {

176. $ scala cli.scala
mean: 82.875

179. 2

180. def sum(list: List[Double]): Double =
list match {
case Nil => 0
case head :: tail => head + sum(tail)
}
def length(list: List[Double]): Double =
list match {
case Nil => 0
case _ :: tail => 1 + length(tail)
}

182. def common(list: List[Double]): Double =
list match {
case Nil => 0
case head :: tail => ??? + common(tail)
}

183. ???

186. def common(list: List[Double], f: Double => Double): Double =
list match {
case Nil => 0
case head :: tail => f(head) + common(tail, f)
}

187. 1

188. sum length

189. def sum(list: List[Double]): Double = common(list, head => head)
def length(list: List[Double]): Double = common(list, _ => 1)

191. head => head _ => 1

192. head => head 1

193. _ => 1 1 1

194. 7-1
_ => 1 head => 1
_

195. match _

196. 7-2

197. def test(fun: Double => Double) = fun(3.14)
test(_ => 1) // 1.0

198. 1

199. val fun = _: Double => 1
test(fun) //

201. :

202. 7-3
identity

203. fold

204. fold

205. common

206. fold

207. fold sum length
map filter

208. def foldr[A, B](f: (A, B) => B, ini: B, list: List[A]): B =
list match {
case Nil => ini
case head :: tail => f(head, foldr(f, ini, tail))
}

209. Double
length sum foldr

210. def length(list: List[Double]): Double =
foldr[Double, Double]((_, i) => i + 1, 0, list)
def sum(list: List[Double]): Double =
foldr[Double, Double]((a, i) => a + i, 0, list)

211. 7-4
foldr

212. max
min
reverse
filter
map