monoid1.scala

def check[A: Equal: Show: Monoid](a: A) = {
  a |+| mzero[A] assert_=== a
  mzero[A] |+| a assert_=== a
}

check(1)

check("Scalaz")

check(List(1, 2, 3))

check(Ikamusume())

semigroup1.scala

case class Ikamusume(syokusyu: Int = 10)

implicit def IkamusumeEqual: Equal[Ikamusume] = equalA

implicit def IkamusumeShow: Show[Ikamusume] = shows("ゲソ" * _.syokusyu)

implicit def IkamusumeSemigroup: Semigroup[Ikamusume] = semigroup(_.syokusyu + _.syokusyu |> Ikamusume)

(Ikamusume() |+| Ikamusume()).shows assert_=== "ゲソゲソゲソゲソゲソゲソゲソゲソゲソゲソゲソゲソゲソゲソゲソゲソゲソゲソゲソゲソ"

semigroup2.scala

1 |+| 1 assert_=== 2

List(1) |+| List(1) assert_=== List(1, 1)

"Hello" |+| "World" assert_=== "HelloWorld"

1.some |+| 1.some assert_=== 2.some

false |+| true assert_=== true

show1.scala

case class ScalaChan(name: String = "Scalaちゃん")

implicit def ScalaChanShow: Show[ScalaChan] = show(_.name.toList)

implicit def ScalaChanShow: Show[ScalaChan] = shows(_.name)

ScalaChan().shows assert_=== "Scalaちゃん"

case class Ikamusume() { override def toString = "イカちゃん" }

implicit def IkamusumeShow: Show[Ikamusume] = showA

Ikamusume().shows assert_=== "イカちゃん"

implicit def SomeShow[A: Show]: Show[Some[A]] = showBy(s => (s: Option[A]))

Some(1).shows assert_=== "Some(1)"

show2.scala

"Scalaz".show assert_=== List('S', 'c', 'a', 'l', 'a', 'z')

"Scalaz".shows assert_=== "Scalaz"

346.shows assert_=== "346"

show3.scala

scala> 1.print
1
scala> "Scalaz".println
Scalaz

show4.scala

implicit def ElemShow: Show[xml.Elem] = showA

<scala>{ "Scalaちゃん".text }</scala> assert_=== <scala>Scalaちゃん</scala>

zero1.scala

mzero[Int] assert_=== 0

mzero[String] assert_=== ""

mzero[List[Int]] assert_=== nil[Int]

mzero[Option[Int]] assert_=== none[Int]

zero2.scala

implicit def IkamusumeZero: Zero[Ikamusume] = zero(Ikamusume(0))

mzero[Ikamusume].shows assert_=== ""

zero3.scala

lazy val geso: Option[Int] => String = _.matchOrZero {
  case Some(n) => "ゲソ" * n
}

geso(2.some) assert_=== "ゲソゲソ"

geso(none) assert_=== ""