Store comonad

# See: https://github.com/fantasyland/fantasy-land#comonad

# data Store b a = Store b (b -> a)
# instance Comonad (Store b)
class Store

  # { value: b, set: (b -> a) } -> Store b a
  constructor: ({@value, @set}) ->
  
  # () -> b
  from: -> @value

  # () -> a
  extract: -> @set @value

  # (a -> c) -> Store b c
  map: (f) -> new Store @value, (b) -> f @set b

  # (Store b a -> b) -> Store b a
  extend: (f) -> new Store (f this), @inject