travisbrown

/** Constructing "singleton types" from compile-time literals
  *
  * val x = Example.foo(42)
  * val y: x.T = 42 // compiles
  * val z: x.T = 43 // doesn't
  *
  */

import scala.language.experimental.macros
import scala.reflect.macros.Context

travisbrown

/** Instantiating a trait with a type member in a macro.
  *
  * Complete working example by Travis Brown for this Stack Overflow question:
  *     http://stackoverflow.com/q/13795490/334519
  */

import scala.language.existentials
import scala.language.experimental.macros

trait TypeBuilder { type fieldType }

edwinb

  -- Idris type classes actually take any kind of value as a parameter,
  -- we're not restricted to Sets or parameterised Sets.
  
  -- So we actually have 'value classes'. It seems we can use type class
  -- resolution to make rudimentary decision procedures, then:
  
  using (xs : List a)
    data Elem : a -> List a -> Set where
         Here  : Elem x (x :: xs)
         There : Elem x xs -> Elem x (y :: xs)

xeno-by

19:07 ~/Projects/Kepler_typemacros/sandbox (topic/typemacros)$ scalac Macros.scala
19:07 ~/Projects/Kepler_typemacros/sandbox (topic/typemacros)$ scala -cp .
Welcome to Scala version 2.10.1-20121120-175733-b60f5bcf2c (Java HotSpot(TM) 64-Bit Server VM, Java 1.6.0_37).
Type in expressions to have them evaluated.
Type :help for more information.

scala> class C extends AnyRef with Macros.Foo[Int]("2")
defined class C

scala> new C().hello

travisbrown

import shapeless._, Nat._

trait FizzBuzz[N <: Nat] {
  type R3 <: Nat
  type R5 <: Nat
 
  def ti: ToInt[N]
  def prev: List[String]
  def d3: R3 =:= _0
  def d5: R5 =:= _0

travisbrown

// Searching for large ModAux instances can be extremely slow. 
// See this version for a faster solution: https://gist.github.com/4108026

import shapeless._, Nat._

trait FizzBuzz[N <: Nat] {
  def steps: List[String]
  def show = println(steps.reverse.mkString("\n"))
}

travisbrown

/**
 * Digging through arbitrarily nested case classes, tuples, and lists
 * by Travis Brown
 *
 * In response to this question by Channing Walton on the Shapeless dev list:
 *
 *     https://groups.google.com/d/msg/shapeless-dev/hn7_U21tupI/Zm9h3uNb51gJ
 *
 * Tested with Scala 2.9.2 and Shapeless 1.2.3. Should work on 1.2.2 with minor edits.
 */

travisbrown

/**
* Type-level Tower of Hanoi
* by Travis Brown
*
* Note: not optimal, and probably won't work for some valid inputs.
* Tested with Scala 2.9.2 and Shapeless 1.2.3.
*/

import shapeless._, Nat._

travisbrown

/**
 * We can use the Scala type system (with help from Miles Sabin's Shapeless
 * library) to solve the bank account number validation problem in the second
 * user story of the KataBankOCR kata on Coding Dojo:
 * 
 * http://codingdojo.org/cgi-bin/wiki.pl?KataBankOCR
 * 
 * By Travis Brown in response to a question by Paul Snively on the Shapeless
 * Dev mailing list:
 *

robinp

package shapeless

import shapeless._
import HList._

package object autoordering extends App {

  type Iso[T, L <: HList] = HListIso[T, L]

  implicit def ccOrdering[C, L <: HList](implicit iso: Iso[C, L], L: Ordering[L]) = new Ordering[C] {