Map diffs, golfed

map_difference.ex

# Compares two maps and generates a list of actions that can be applied to the
# first map to transform it into the second.
#
#   diff = difference(m1, m2)
#   apply(m1, diff) === m2

defmodule MapDiffGolf do

  def difference(%{} = m1, %{} = m2), do:
    for {k, v} <- m2,
      not match?(%{^k => ^v}, m1),
      into: (for {k, _} <- m1, not Map.has_key?(m2, k), do: {:del, k}),
      do: {:put, k, v}

  def apply(%{} = m, [_|_] = d), do:
    Enum.reduce d, m, fn
      {:put, k, v}, m -> Map.put m, k, v
      {:del, k}, m -> Map.delete m, k
    end
    
end