1
我想這個Applicative validation syntax例如轉換成Scalaz 7 +無形2.0應用型驗證語法scalaz +無形2.0
//for jupyter-scala kernel
//classpath.add("org.scalaz" %% "scalaz-core" % "7.2.7")
//classpath.add("com.chuusai" %% "shapeless" % "2.3.2")
case class Foo(a: Int, b: Char, c: String)
首先Scalaz語法
import scalaz._
import Scalaz._
type ErrorsOr[A] = ValidationNel[String, A]
type Validator[A] = String => ErrorsOr[A]
val checkA: Validator[Int] = (s: String) =>
try s.toInt.success catch {
case _: NumberFormatException => "Not a number!".failureNel
}
val checkB: Validator[Char] = (s: String) =>
if (s.size != 1 || s.head < 'a' || s.head > 'z') {
"Not a lower case letter!".failureNel
} else s.head.success
val checkC: Validator[String] = (s: String) =>
if (s.size == 4) s.success else "Wrong size!".failureNel
def validateFoo(a: String, b: String, c: String) =
(checkA(a) |@| checkB(b) |@| checkC(c))(Foo.apply _)
println(validateFoo("ab", "cd", "ef"))
//Failure(NonEmpty[Not a number!,Not a lower case letter!,Wrong size!])
println(validateFoo("42", "cd", "ef"))
//Failure(NonEmpty[Not a lower case letter!,Wrong size!])
def validateFoo2(a: String, b: String, c: String):Validation[NonEmptyList[String], Foo] =
checkC(c) <*> (checkB(b) <*> (checkA(a) map (Foo.apply _).curried))
println(validateFoo2("42", "cd", "ef"))
//Failure(NonEmpty[Not a lower case letter!,Wrong size!])
到目前爲止好，現在進入無形2.0
import shapeless._
import shapeless.ops.hlist._
import shapeless.ops.function._
import shapeless.poly._
import shapeless.syntax.std.function._
object applier extends Poly2 {
implicit def ap[F[_]: Applicative, H, T <: HList, R]:
Case2.Aux[applier.type, F[(H :: T) => R], F[H], F[T => R]] =
at[F[(H :: T) => R], F[H]](
(f, fa) => fa <*> f.map(hf => (h: H) => (t: T) => hf(h :: t))
)
}
class Lifter[F[_]: Applicative] {
def lift[G, H, A <: HList, M <: HList, R](g: G)(implicit
hlG: FnToProduct.Aux[G, A => R],
mapped: Mapped.Aux[A, F, M],
unH: FnFromProduct.Aux[M => F[R], H],
folder: LeftFolder.Aux[M, F[A => R], applier.type, F[HNil => R]]
) = unH((m: M) => folder(m, hlG(g).point[F]).map(_(HNil)))
}
def into[F[_]: Applicative] = new Lifter[F]
val liftedFoo = into[ErrorsOr] lift (Foo.apply _)
def validateFooGeneric(a: String, b: String, c: String) =
liftedFoo(checkA(a), checkB(b), checkC(c))
println(validateFooGeneric("42", "cd", "ef"))
//Failure(NonEmpty[Not a lower case letter!,Wrong size!])
現在最後一點
所有的編譯，但是當一個人試圖使用它，例如：
val validateFooShapeless = validate(Foo.apply _)(checkA :: checkB :: checkC :: HNil)
我得到一個錯誤
could not find implicit value for parameter mapped: shapeless.ops.hlist.Mapped.Aux[A,F,M]
validate(Foo.apply _)(checkA :: checkB :: checkC :: HNil)
^
任何想法，三分球，將不勝感激