Proof of concept translation of some Scalding examples (https://github.com/twitter/scalding/wiki/Fields-based-API-Reference) to shapeless records (https://github.com/milessabin/shapeless/wiki/Feature-overview:-shapeless-2.0.0#extensible-records)

gistfile1.scala

import shapeless._
import record._
import syntax.singleton._

object ScaldingPoC extends App {

  // map, flatMap
  val birds =
    List(
      "name" ->> "Swallow (European, unladen)" :: "speed" ->> 23 :: "weightLb" ->> 0.2 :: "heightFt" ->> 0.65 :: HNil,
      "name" ->> "African (European, unladen)" :: "speed" ->> 24 :: "weightLb" ->> 0.21 :: "heightFt" ->> 0.6 :: HNil
    )

  val fasterBirds = birds.map(b => b + ("doubleSpeed" ->> b("speed")*2))
  fasterBirds foreach println

  val britishBirds = birds.map(b => b + ("weightKg" ->> b("weightLb")*0.454) + ("heightM" ->> b("heightFt")*0.305))
  britishBirds foreach println

  val items =
    List(
      "author" ->> "Benjamin Pierce" :: "title"  ->> "Types and Programming Languages" :: "price"  ->>  49.35 :: HNil,
      "author" ->> "Roger Hindley" :: "title"  ->> "Basic Simple Type Theory" :: "price"  ->> 23.14 :: HNil
    )

  val pricierItems = items.map(i => i + ("price" ->> i("price")*1.1))
  pricierItems foreach println

  val books =
    List(
      "text" ->> "Not everyone knows how I killed old Phillip Mathers" :: HNil,
      "text" ->> "No, no, I can't tell you everything" :: HNil
    )

  val lines = books.flatMap(book => for(word <- book("text").split("\\s+")) yield book + ("word" ->> word))
  lines foreach println
}  

@johnynek The keys don't exist at all at runtime.

Here's an example showing Kryo serialization of record types: https://gist.github.com/bsidhom/9798005

The record type takes no more space than its underlying HList, which isn't too bad when registered. I haven't found a way to register classes more concisely unfortunately, but it may be possible to remove some boilerplate given an example instance (via getClass) or with the help of macros.