Tupling big HLists

gistfile1.scala

import shapeless._

// if there's only one element, return it
trait ToTuple2 extends Poly1 {
  implicit def h2[T] = at[T :: HNil] { case t :: HNil => t }
}
// if there are at least 2 elements, tuple them
trait ToTuple1 extends ToTuple2 {
  implicit def h1[T1, T2, L <: HList, T <: T1 :: T2 :: L](implicit tupler: Tupler[T1 :: T2 :: L]) = at[T1 :: T2 :: L] { 
    case l @ (t1 :: t2 :: rest)  => l.tupled
  }
}
// if there are more than 21 elements, tuple the first 21s and recursively tuple the rest
trait ToTuple0 extends ToTuple1 {
  implicit def h0[T1,T2,T3,T4,T5,T6,T7,T8,T9,T10,T11,T12,T13,T14,T15,T16,T17,T18,T19,T20,T21,R <: HList](implicit c: Case1[R]) = 
    at[T1::T2::T3::T4::T5::T6::T7::T8::T9::T10::T11::T12::T13::T14::T15::T16::T17::T18::T19::T20::T21::R] {  
    case t1::t2::t3::t4::t5::t6::t7::t8::t9::t10::t11::t12::t13::t14::t15::t16::t17::t18::t19::t20::t21::rest => 
      (t1,t2,t3,t4,t5,t6,t7,t8,t9,t10,t11,t12,t13,t14,t15,t16,t17,t18,t19,t20,t21,c(rest))
  }
}

object toTuple extends ToTuple0

toTuple(1::2::3::4::5::HNil)
// (1,2,3,4,5)

toTuple(1::2::3::4::5::6::7::8::9::10::11::12::13::14::15::16::17::18::19::20::21::22::HNil)
// (1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22)

toTuple(1::2::3::4::5::6::7::8::9::10::11::12::13::14::15::16::17::18::19::20::21::22::23::24::HNil)
//(1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,(22,23,24))