1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
|
trait Functor[F[_]] {
def map[A,B](fa: F[A], f: A => B): F[B]
}
trait ComposeT[F[_],G[_]] {
type Apply[A] = F[G[A]]
}
case class Compose[F[_],G[_]]() {
def Functor(implicit f: Functor[F], g: Functor[G]): Functor[ComposeT[F,G]#Apply] =
new Functor[ComposeT[F,G]#Apply] {
def map[A,B](c: ComposeT[F,G]#Apply[A], h: A => B) =
f.map(c, (x:G[A]) => g.map(x,h))
}
}
object Cat {
def compose[F[_],G[_]] = Compose[F,G]()
}
object Functors {
implicit val List = new Functor[List] {
def map[A,B](fa: List[A], f: A => B): List[B] = fa map f
}
implicit val Option = new Functor[Option] {
def map[A,B](fa: Option[A], f: A => B): Option[B] = fa map f
}
}
object Main {
import Functors._
val cf = Cat.compose[List,Option].Functor
}
|
