Scala 3 macro to return lambda

gistfile1.txt

type Params[N <: Num] <: Tuple = N match {
  case 0 => EmptyTuple
  case _ => Double *: Params[N - 1]
}

type Num = Singleton & Int
opaque type Multivector[DIM <: Num] = Array[Double]

transparent inline def vector[N <: Num](using v: ValueOf[N], ev: (N > 0) =:= true): Params[N] => Multivector[N] =
  ${ vectorImpl[N]('{valueOf[N]}) }

def vectorImpl[N <: Num: Type](v: Expr[Int])(using q: Quotes): Expr[Params[N] => Multivector[N]] = {
  import q.reflect.*
  val dim = v.valueOrAbort

  val mtpe = MethodType(List("basis"))(
    _ => List(TypeRepr.of[Params[N]]),
    _ => TypeRepr.of[Multivector[N]]
  )

  val constructor = Lambda(
    Symbol.spliceOwner,
    mtpe,
    { case (methSym, List(basis)) =>
      given Quotes = methSym.asQuotes

      '{
        val edim = ${Expr(dim)}
        val m: Params[N] = ${ basis.asExprOf[Params[N]] }
        val arr = Array.fill(edim)(0d)
        var i = 0

        for (v <- m.productIterator) {
          arr(i) = v.asInstanceOf[Double]
          i += 1
        }

        _vector(edim)(arr*).asInstanceOf[Multivector[N]]
      }.asTerm
    }
  )

  constructor.asExprOf[Params[N] => Multivector[N]]
}