Checksum at the Type Level using Shapeless

问题

I came up with the following per this problem:

package net

import shapeless.{::, HNil, _}
import ops.hlist.IsHCons
import nat._
import ops.nat.{Mod, Prod, Sum}

trait IsValid[A]
object IsValid {

  def apply[L <: HList](implicit ev: IsValid[L]) = ev

  //  account number:  3  4  5  8  8  2  8  6  5
  //  position names:  d9 d8 d7 d6 d5 d4 d3 d2 d1
  //
  //  checksum calculation:
  //    (d1+2*d2+3*d3 +..+9*d9) mod 11 = 0
  implicit def validNumber[D9 <: Nat, D8 <: Nat, D7 <: Nat, D6 <: Nat, D5 <: Nat, D4 <: Nat, D3 <: Nat, D2 <: Nat, D1 <: Nat,
                           P9 <: Nat, P8 <: Nat, P7 <: Nat, P6 <: Nat, P5 <: Nat, P4 <: Nat, P3 <: Nat, P2 <: Nat, P1 <: Nat,
                           S1 <: Nat, S2 <: Nat, S3 <: Nat, S4 <: Nat, S5 <: Nat, S6 <: Nat, S7 <: Nat, S8 <: Nat](
    implicit p9: Prod.Aux[D9, _9, P9],
    p8 : Prod.Aux[D8, _8, P8],
    p7 : Prod.Aux[D7, _7, P7],
    p6 : Prod.Aux[D6, _6, P6],
    p5 : Prod.Aux[D5, _5, P5],
    p4 : Prod.Aux[D4, _4, P4],
    p3 : Prod.Aux[D3, _3, P3],
    p2 : Prod.Aux[D2, _2, P2],
    p1 : Prod.Aux[D1, _1, P1],
    s1: Sum.Aux[P9, P8, S1],
    s2: Sum.Aux[P7, S1, S2],
    s3: Sum.Aux[P6, S2, S3],
    s4: Sum.Aux[P5, S3, S4],
    s5: Sum.Aux[P4, S4, S5],
    s6: Sum.Aux[P3, S5, S6],
    s7: Sum.Aux[P2, S6, S7],
    s8: Sum.Aux[P1, S7, S8],
    mod: Mod.Aux[S8, _11, _0]
  ): IsValid[D9 :: D8 :: D7 :: D6 :: D5 :: D4 :: D3 :: D2 :: D1 :: HNil] = {
    new IsValid[D9 :: D8 :: D7 :: D6 :: D5 :: D4 :: D3 :: D2 :: D1 :: HNil] {}
  }


}

It appears to work for the 0 case:

scala> import net.IsValid, shapeless._, nat._
import net.IsValid
import shapeless._
import nat._

scala> IsValid[_0 :: _0 :: _0 :: _0 :: _0 :: _0 :: _0 :: _0 :: _0 :: HNil]
res0: net.IsValid[shapeless.::...

But, when I call the following "valid" combination, the console shows no output, i.e. hangs.

scala> IsValid[_3 :: _4 :: _5 :: _8 :: _8 :: _2 :: _8 :: _6 :: _5 :: HNil]

I only waited ~2 minutes before asking this question.

I'm assuming that it's doing the implicit lookups, but I'm not sure.

Why does the above call hang? Perhaps there's an error in my code?

来源：https://stackoverflow.com/questions/42092034/checksum-at-the-type-level-using-shapeless

标签

scala

shapeless