Created
July 6, 2015 10:37
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| import shapeless._ | |
| import syntax._ | |
| import poly._ | |
| object LeftFolderOps { | |
| trait LeftFolder[C <: Coproduct, In, F] extends Serializable { | |
| def apply(c: C, in: In): In | |
| } | |
| object LeftFolder { | |
| def apply[C <: Coproduct, In, F](implicit folder: LeftFolder[C, In, F]) = folder | |
| implicit def hdLeftFolder[H, In, F] | |
| (implicit f: Case2.Aux[F, In, H, In]): LeftFolder[H :+: CNil, In, F] = new LeftFolder[H :+: CNil, In, F] { | |
| def apply(c: H :+: CNil, in: In): In = c match { | |
| case Inl(h) => f(in, h) | |
| case Inr(t) => in | |
| } | |
| } | |
| implicit def tlLeftFolder[H, T <: Coproduct, In, F] | |
| (implicit st: LeftFolder[T, In, F], f: Case2.Aux[F, In, H, In]): LeftFolder[H :+: T, In, F] = new LeftFolder[H :+: T, In, F] { | |
| def apply(c: H :+: T, in: In) = | |
| c match { | |
| case Inl(h) => f(in, h) | |
| case Inr(t) => st(t, in) | |
| } | |
| } | |
| } | |
| } | |
| final class LeftFolderOps[C <: Coproduct](c: C) extends Serializable { | |
| def foldLeft[In](z: In)(op: Poly)(implicit folder: LeftFolderOps.LeftFolder[C, In, op.type]): In = folder(c, z) | |
| } | |
| object CoproductLeftFolderSyntax { | |
| implicit def coproductOps[C <: Coproduct](c: C): LeftFolderOps[C] = new LeftFolderOps(c) | |
| } | |
| import CoproductLeftFolderSyntax._ | |
| type IS = Int :+: String :+: Boolean :+: CNil | |
| val isi = Coproduct[IS](10) | |
| val iss = Coproduct[IS]("foo") | |
| val isb = Coproduct[IS](true) | |
| object size extends Poly1 { | |
| implicit def caseInt = at[Int](_ => 1) | |
| implicit def caseString = at[String](_.length) | |
| implicit def caseBoolean = at[Boolean](_ => 42) | |
| } | |
| object wonkyAddSize extends Poly2 { | |
| implicit def default[T](implicit st: size.Case.Aux[T, Int]) = | |
| at[Int, T] { (acc, t) => if (acc > 42) acc - size(t) else acc + size(t) } | |
| } | |
| isi.foldLeft(0)(wonkyAddSize) // 1 | |
| iss.foldLeft(42)(wonkyAddSize) // 45 | |
| isb.foldLeft(43)(wonkyAddSize) // 1 |
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