My crib sheet from the shapeless workshop @ Scala IO.

gistfile1.scala

package scalaio

import shapeless._, poly._

object list extends (Id ~> List) {
  def apply[T](t : T) = List(t)
}

object headOption extends (List ~> Option) {
  def apply[T](l : List[T]) = l.headOption
}

object plus extends Poly2 {
  implicit val caseInt = at[Int, Int](_ + _)
}

object inc extends ->((i: Int) => i+1)

object hinc extends Poly1 {
  implicit val caseInt = at[Int](_+1)
  implicit val caseString = at[String](_+"*")
  implicit val caseBoolean = at[Boolean](!_)
}

object TupleDemo {

import syntax.std.tuple._

val t = (23, "foo", true)

// Heads and tails
t.head
t.tail

t.last
t.init

// : t t.tail.tail.tail ... Unit

// Come back to indexing/updating/splitting

// Append, prepend, concat
1.0 +: t
t :+ 1.0

val u = (1.0, 'a')
t ++ u

() ++ t == t  // tuples are monoids wrt Unit and ++
t ++ () == t

// map, flatMap
val t1 = t map list
t1 map headOption

val v = ((23, "foo"), (), (1.0, true, 'c'))
v flatMap identity

val w = (1, 2, 3, 4, 5)
w.foldLeft(0)(plus)

// zip, unzip, transpose
val x = ((23, "foo"), (true, 1.0), ('c', 13))
val x1 = x.zip
val x2 = x1.unzip

x.transpose // .transpose.transpose

val v0 = (1.0, 0.0, 0.0)
val v1 = (2.0, 3.0, 0.0)
val v2 = (4.0, 5.0, 6.0)
val m = (v0, v1, v2)
m.transpose

// toList
v0.toList

// productElements
t.productElements
}

object GenericDemo {

case class Address(street: String, number: Int, city: String, country: String)
case class Person(name: String, age: Int, address: Address)

val suesAddress = Address("North Street", 23, "Brighton", "UK")
val sue = Person("Sue", 32, suesAddress)

val pgen = Generic[Person]
val agen = Generic[Address]

// to
agen.to(suesAddress)
pgen.to(sue)

// from
val johnsAddressl = "South Street" :: 13 :: "Bristol" :: "UK" :: HNil
val johnsAddress = agen.from(johnsAddressl)
val johnl = "John" :: 31 :: johnsAddress :: HNil
val john = pgen.from(johnl)

// low level slicing and dicing
val mtownl = agen.to(pgen.to(sue).tail.tail.head).drop(2)
val jstreetl = agen.to(pgen.to(john).tail.tail.head).take(2)
val fixedl = jstreetl ++ mtownl
val fixed = agen.from(fixedl)

// Lenses
val streetLens = Lens[Person] >> 2 >> 0
streetLens.get(john)
streetLens.set(john)("East Street")

// Zipper
import Zipper._

val jz = john.toZipper
jz.right.right.down.put("West Street").root.reify

// Coproducts, Scrap Your Boilerplate, recursion

sealed trait Tree[T]
case class Leaf[T](t: T) extends Tree[T]
case class Node[T](left: Tree[T], right: Tree[T], name: String = "Foo") extends Tree[T]
  
Generic[Leaf[Int]]
Generic[Node[Int]]
Generic[Tree[Int]] // Abstract, recursive

// Compare: product
val isb = 23 :: "foo" :: true :: HNil
isb map hinc
everywhere(hinc)(isb)

// Compare: coproduct/sum
type ISB = Int :+: String :+: Boolean :+: CNil
val i = Coproduct[ISB](23)
val s = Coproduct[ISB]("foo")
val b = Coproduct[ISB](true)

i map hinc
s map hinc
b map hinc

everywhere(hinc)(i)
everywhere(hinc)(s)
everywhere(hinc)(b)

// Sum of products ... with recursion!
val tree: Tree[Int] =
  Node(
    Node(
      Node(
        Leaf(1),
        Node(
          Leaf(2),
          Leaf(3)
        )
      ),
      Leaf(4)
    ),
    Node(
      Leaf(5),
      Leaf(6)
    )
  )

everywhere(inc)(tree)
}

object SingletonDemo {

val foo = "foo"
val foo2 : foo.type = foo // nb. not "foo"

// No 23.type/"foo".type/true.type

import syntax.singleton._

23.narrow
"foo".narrow
true.narrow

val wFoo = Witness("foo")
val wBar = Witness("bar")
val wBaz = Witness("baz")
type Foo = wFoo.T
type Bar = wBar.T
type Baz = wBaz.T

val w0 = Witness(0)
val w1 = Witness(1)
val w2 = Witness(2)
type _0 = w0.T
type _1 = w1.T
type _2 = w2.T

val wT = Witness(true)
val wF = Witness(false)
type True = wT.T
type False = wF.T

// Type classes indexed by values
trait Choose[B <: Boolean, T] {
  def apply() : T
}

object Choose {
  implicit val chooseTrue = new Choose[True, String] {
    def apply() = "Foo"
  }

  implicit val chooseFalse = new Choose[False, Int] {
    def apply() = 23
  }
}

def choose[T](b: Witness.Lt[Boolean])(implicit choose: Choose[b.T, T]): T = choose()

// HLists and tuples indexed by Int literals

object Index {
import syntax.std.tuple._

val t = (23, "foo", true)
t(1)
t.updatedAt(1, 2.0)
t.split(1)

val l = 23 :: "foo" :: true :: HNil
l(1)
l.updatedAt(1, 2.0)
l.split(1)   // ._1, ._2 vs. resX(0), resX(1)
}

// Records with singleton literal keys

import record._, syntax.singleton._

val field = "foo" -> 23
val sfield = "foo" ->> 23

def value[K, V](f: FieldType[K, V]): V = f
def key[K, V](f: FieldType[K, V])(implicit wKey: Witness.Aux[K]): K = wKey.value

val book =
  ("author" ->> "Benjamin Pierce") ::
  ("title"  ->> "Types and Programming Languages") ::
  ("id"     ->>  262162091) ::
  ("price"  ->>  44.99) ::
  HNil

book("author")
book("price")
val book1 = book + ("price" ->> 39.99)
book("price")

book.values // .tupled
book.keys   // .tupled
}

object IllTypedDemo {
import test.illTyped

//illTyped(""" 23 : Int """)
illTyped(""" 23 : String """)

//val liar : Unit = illTyped(""" liar """)

}


// Sized take and drop