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/**
 * Exercises explaining covariant and contravariant functors.
 * 
 * Additionally exercises explaining variance of types over their type parameters.
 *
 * Implement the `???` functions. Are all implementable?
 */
  
trait Functors {
  /**

alissapajer

import java.util.concurrent.ConcurrentHashMap

object Why {
  val data = new ConcurrentHashMap[Int, String]

  def update(int: Int, str: String): Unit = {
    data.put(int, str)
  }
}

alissapajer

-- https://haskell.fpcomplete.com/user/DanBurton/20-intermediate-exercises
-- Originally from http://blog.tmorris.net/posts/20-intermediate-haskell-exercises/

class Fluffy f where
  furry :: (a -> b) -> f a -> f b

-- Exercise 1
-- Relative Difficulty: 1
instance Fluffy [] where
  furry = fmap

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backpack
pack cover
hiking poles
sleeping bag
sleeping pad
tent

water bottles
camelback
water purification system