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

import java.io.{ BufferedReader, File, FileReader }
import scalaz._, Scalaz._, effect.IO, iteratee.{ Iteratee => I, _ }

object IterateeIOExample {
  type ErrorOr[A] = Either[Throwable, A]

  def openFile(f: File) = IO(new BufferedReader(new FileReader(f)))
  def readLine(r: BufferedReader) = IO(Option(r.readLine))
  def closeReader(r: BufferedReader) = IO(r.close())

travisbrown

import java.io.{ BufferedReader, File, FileReader }
import scalaz._, Scalaz._, effect.IO, iteratee.{ Iteratee => I, _ }

object IterateeIOExample {
  type ErrorOr[A] = EitherT[IO, Throwable, A]

  def openFile(f: File) = IO(new BufferedReader(new FileReader(f)))
  def readLine(r: BufferedReader) = IO(Option(r.readLine))
  def closeReader(r: BufferedReader) = IO(r.close())

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

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

import scalaz._
import scalaz.std.option._
import scalaz.syntax.functor._

trait Inc extends (Int => Int) {
  implicit def incToLiftable(i: this.type): {
    def lift(implicit F: Functor[Option]): Option[Int] => Option[Int]
  } = implicitly[this.type => LiftV[Option, Int, Int]].apply(i)
  def apply(x: Int) = x + 1
}

travisbrown

/**
* Related to this question: http://stackoverflow.com/q/13663216/334519
*
* Unhelpful error message:
* scala> MacroExample.foo(List(1, 2, 3): _*)
* <console>:8: error: no `: _*' annotation allowed here
* (such annotations are only allowed in arguments to *-parameters)
*               MacroExample.foo(List(1, 2, 3): _*)
*                                             ^
*

travisbrown

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

object WrapperExample {
  def wrap[A](a: A): A = macro wrap_impl[A]

  def wrap_impl[A: c.WeakTypeTag](c: Context)(a: c.Expr[A]) = {
    import c.universe._

    val wrapped = weakTypeOf[A]

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 }

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