Saving different working use cases using Elixir metaprogramming

elixir_meta.ex

###################################################
### Solution to `invalid quoted expression`
### short version: use `Macro.escape/1`
###
### https://elixirforum.com/t/cant-seem-to-unquote-a-map/4009
###################################################

    ########################################
    ### (1) do smth with map, tuple etc.
    ###     but only in the body of the
    ###     dynamically defined function
    ########################################

defmodule A do
  defmacro inject_map(arg) do
    quote bind_quoted: [arg: arg] do
      def balabab, do: unquote(arg)
    end
  end
end

defmodule C do
  require A
  A.inject_map(Macro.escape(%{lofa: 7}))
end

C.balabab #> %{lofa: 7}

    ##########################################
    ### (2) if map, tuple etc. needs massaging
    ###     outside the dynamically defined
    ###     function body
    ##########################################
defmodule A do
  defmacro inject_map(arg) do
    quote bind_quoted: [arg: arg] do
      IO.inspect arg
      #########################
      # {:%{}, [], [lofa: 7]}
      # so you can match it the last item of the tuple
      # and restore it to map with `Enum.into/2`
      # see https://github.com/society-for-the-blind/timesheets/blob/master/lib/timesheets/excel_date.ex
      #########################
      def balabab, do: unquote(arg)
    end
  end
end

defmodule C do
  require A
  A.inject_map(Macro.escape(%{lofa: 7}))
end

    ##########################################
    ### (3) to make it a complete circle,
    ###     `IO.inspect/1` is now before `quote`
    ##########################################
defmodule A do
  defmacro inject_map(arg) do
    IO.inspect arg
    #######################
    # good luck with that
    # {{:., [line: 5], [{:__aliases__, [counter: 0, line: 5], [:Macro]}, :escape]},
    #  [line: 5], [{:%{}, [line: 5], [lofa: 7]}]
    # }
    #######################
    quote bind_quoted: [arg: arg] do
      def balabab, do: unquote(arg)
    end
  end
end

defmodule C do
  require A
  A.inject_map(Macro.escape(%{lofa: 7}))
end

##################################################
### Getting to the Elixir macro that dynamically 
### creates multiple functions
##################################################

### try no 1 ###
defmodule SwapMaker do
  defmacro make_fixed_swapper(left, right) do
    quote bind_quoted: [l: left, r: right] do
      def fixed_swapper(unquote(l)), do: unquote(r)
      def fixed_swapper(unquote(r)), do: unquote(l)
    end
  end

  def generate_multiple_fixed_swappers(pairs) do
    for {left, right} <- pairs do
      make_fixed_swapper(left, right)
    end
  end
end

defmodule TestingGrounds do
  require SwapMaker
  SwapMaker.make_fixed_swapper(:a,27)
end
# RESULTS:
# wouldn't even compile because
# "** (ArgumentError) cannot invoke def/2 inside function/macro"

### try no 2 ###
defmodule SwapMaker do
  defmacro make_fixed_swapper(left, right) do
    quote bind_quoted: [l: left, r: right] do
      def fixed_swapper(unquote(l)), do: unquote(r)
      def fixed_swapper(unquote(r)), do: unquote(l)
    end
  end

  def generate_multiple_fixed_swappers(pairs) do
    for {left, right} <- pairs do
      quote do
        make_fixed_swapper(unquote(left), unquote(right))
      end
    end
  end
end

defmodule TestingGrounds do
  require SwapMaker
  SwapMaker.make_fixed_swapper(:a,27)
  SwapMaker.generate_multiple_fixed_swappers([{:b,7}, {:c, 23}])
end
# RESULTS:
# closer but instead of generating a def it returns the quoted def

### try no 3 ###
defmodule Swapper do
  defmodule Helper do
    defmacro make_fixed_swapper(left, right) do
      quote bind_quoted: [l: left, r: right] do
        def fixed_swapper(unquote(l)), do: unquote(r)
        def fixed_swapper(unquote(r)), do: unquote(l)
      end
    end
  end

  defmodule Maker do
    require Helper
    defmacro generate_multiple_fixed_swappers(pairs) do
      for {left, right} <- pairs do
        quote do
          Helper.make_fixed_swapper(unquote(left), unquote(right))
        end
      end
    end
  end
end

defmodule TestingGrounds do
  require Swapper.Maker
  require Swapper.Helper
  Swapper.Helper.make_fixed_swapper(:a,27)
  Swapper.Maker.generate_multiple_fixed_swappers([{:b,7}, {:c, 23}])
end
 # RESULTS:
 # It's a miracle!

### try no 4 ###
defmodule Swapper do
  defmodule Helper do
    defmacro make_fixed_swapper(left, right) do
      quote bind_quoted: [l: left, r: right] do
        def fixed_swapper(unquote(l)), do: unquote(r)
        def fixed_swapper(unquote(r)), do: unquote(l)
      end
    end
  end

  defmodule Maker do
    require Helper
    defmacro generate_multiple_fixed_swappers(pairs) do
      quote do
        for {left, right} <- unquote(pairs) do
          Helper.make_fixed_swapper(left, right)
        end
      end
    end
  end
end

defmodule TestingGrounds do
  require Swapper.Maker
  require Swapper.Helper
  Swapper.Helper.make_fixed_swapper(:a,27)

  list = [{:b,7}, {:c, 23}]
  Swapper.Maker.generate_multiple_fixed_swappers(list)
end
# RESULTS:
# It's a miracle!

### try no 5 (exercise is overcomplication) ###
defmodule Swapper do
  defmodule Helper do
    defmacro make_custom_swapper(name, left, right) do
      quote bind_quoted: [n: name, l: left, r: right] do
        def unquote(:"#{n}_swapper")(unquote(l)), do: unquote(r)
        def unquote(:"#{n}_swapper")(unquote(r)), do: unquote(l)
      end
    end
  end

  defmodule Maker do
    require Helper
    defmacro generate_multiple_custom_swappers(pairs) do
      quote do
        for {n,l,r} <- unquote(pairs) do
          Helper.make_custom_swapper(n,l,r)
        end
      end
    end
  end
end

defmodule TestingGrounds do
  require Swapper.Maker
  require Swapper.Helper
  Swapper.Helper.make_custom_swapper(:lofa,:a,27)

  letters = String.split("abcdefghijklmnopqrstuvwxyz", "", trim: true)

  letter_swapper_list =
    for l <- letters do
      {:letter, l, String.upcase(l)}
    end

  things_to_swap = [{:eclipse, "moon", "sun"}|letter_swapper_list]

  Swapper.Maker.generate_multiple_custom_swappers(things_to_swap)
end
# RESULTS:
# The cake is not a lie after all.

### try no 6 (exercise is overcomplication) ###
defmodule Swapper do
  defmodule Helper do
    defmacro make_custom_swapper(name, left, right) do
      quote bind_quoted: [n: name, l: left, r: right] do
        def unquote(:"#{n}_swapper")(unquote(l)), do: unquote(r)
        def unquote(:"#{n}_swapper")(unquote(r)), do: unquote(l)
      end
    end
  end

  defmodule Maker do
    @after_compile __MODULE__

    def __after_compile__(env, _bc) do
      require __MODULE__
      generate_multiple_custom_swappers(:stuff, 7, 9)
    end

    require Helper
    defmacro generate_multiple_custom_swappers(pairs) do
      quote do
        for {n,l,r} <- unquote(pairs) do
          Helper.make_custom_swapper(n,l,r)
        end
      end
    end
  end
end

defmodule TestingGrounds do
  require Swapper.Maker
  require Swapper.Helper
  Swapper.Helper.make_custom_swapper(:lofa,:a,27)

  letters = String.split("abcdefghijklmnopqrstuvwxyz", "", trim: true)

  letter_swapper_list =
    for l <- letters do
      {:letter, l, String.upcase(l)}
    end

  things_to_swap = [{:eclipse, "moon", "sun"}|letter_swapper_list]

  Swapper.Maker.generate_multiple_custom_swappers(things_to_swap)
end
# RESULTS:
# Won't compile
# ** (CompileError) iex:15: you are trying to use the module Swapper.Maker which is currently being defined.

### try no 7 (exercise is overcomplication) ###
defmodule Swapper do
  defmodule Helper do
    defmacro make_custom_swapper(name, left, right) do
      quote bind_quoted: [n: name, l: left, r: right] do
        def unquote(:"#{n}_swapper")(unquote(l)), do: unquote(r)
        def unquote(:"#{n}_swapper")(unquote(r)), do: unquote(l)
      end
    end
  end

  defmodule Maker do
    require Helper
    defmacro generate_multiple_custom_swappers(pairs) do
      quote do
        for {n,l,r} <- unquote(pairs) do
          Helper.make_custom_swapper(n,l,r)
        end
      end
    end
  end

  require Helper
  Helper.make_custom_swapper(:stuff, 7, 9)
end

defmodule TestingGrounds do
  require Swapper.Maker
  require Swapper.Helper
  Swapper.Helper.make_custom_swapper(:lofa,:a,27)

  letters = String.split("abcdefghijklmnopqrstuvwxyz", "", trim: true)

  letter_swapper_list =
    for l <- letters do
      {:letter, l, String.upcase(l)}
    end

  things_to_swap = [{:eclipse, "moon", "sun"}|letter_swapper_list]

  Swapper.Maker.generate_multiple_custom_swappers(things_to_swap)
end
# RESULTS:
# Won't compile
# ** (CompileError) iex:22: module Swapper.Helper is not loaded but was defined. This happens when you depend on a module in the same context it is defined.

#######################################################
# saving values into variables in macros and using them
#######################################################

   ##################################################
   ### (A) using function from same module than macro
   ##################################################
defmodule A do
  def lofa do
    27
  end

  defmacro vmi do
    v = lofa()
    quote do
      def balabab, do: unquote(v)
    end
  end
end

defmodule C do
  require A
  A.vmi
end

C.balabab #>27

   ##################################################
   ### (B) using function from same module than macro
   ###     but calling it with a parameter 
   ###     (macro and function both)
   ##################################################

defmodule A do
  def lofa(dolog) do
    dolog + 27
  end

  defmacro vmi(arg) do
    quote bind_quoted: [arg: arg] do
      v = A.lofa(arg)
      def balabab, do: unquote(v)
    end
  end
end

defmodule C do
  require A
  A.vmi(2)
end

C.balabab #> 29

###########################
# some extras along the way
###########################
# great reads:
#  (1) https://thepugautomatic.com/2015/10/understanding-elixir-macros/
#  (2) http://stackoverflow.com/questions/34300162/elixir-macro-expansion-problems-but-only-in-a-comprehension

defmodule A do
  defmacro lofa(a) do
    quote bind_quoted: [portekak: a] do
      for x <- portekak do
        IO.puts x
      end
      Enum.each(portekak, fn(x) -> IO.puts(x) end)
    end
  end
end

defmodule C do
  require A
  a = [:a, 27]
  A.lofa a
end
# RESULTS: (this gets printed immediately)
# 27
# a
# 27
# a

defmodule A do
  defmacro lofa(a) do
    quote bind_quoted: [porteka: a] do
      def vmi(porteka) do
        unquote(porteka)
        # IO.puts a
      end
    end
  end
end

defmodule C do
  require A
  a = "11/27/2017"
  A.lofa a
end
# RESULTS:
# iex(4)> C.vmi "11/27/2017"
# "11/27/2017"
# iex(5)> C.vmi "11/27/2019"
# "11/27/2017"


defmodule A do
  defmacro lofa(a) do
    quote bind_quoted: [porteka: a] do
      def vmi(unquote(porteka)) do
        unquote(porteka)
        # IO.puts a
      end
    end
  end
end

defmodule C do
  require A
  a = "11/27/2017"
  A.lofa a
end
# RESULTS
# iex(9)> C.vmi "11/27/2017"
# "11/27/2017"
# iex(10)> C.vmi "11/27/2019"
# ** (FunctionClauseError) no function clause matching in C.vmi/1
#     iex:11: C.vmi("11/27/2019")

defmodule A do
  defmacro lofa(a) do
    quote bind_quoted: [porteka: a] do
      def vmi(unquote(porteka)) do
        porteka
        # IO.puts a
      end
    end
  end
end

defmodule C do
  require A
  a = "11/27/2017"
  A.lofa a
end
# RESULTS
# wouldn't compile ("undefined function porteka/0")

defmodule A do
  defmacro lofa(a) do
    quote bind_quoted: [porteka: a] do
      def vmi(unquote(porteka) = p) do
        p
        # IO.puts a
      end
    end
  end
end

defmodule C do
  require A
  alamizsna = "11/27/2017"
  A.lofa alamizsna
end
# RESULTS
# iex(9)> C.vmi "11/27/2017"
# "11/27/2017"
# iex(10)> C.vmi "11/27/2019"
# ** (FunctionClauseError) no function clause matching in C.vmi/1
#     iex:11: C.vmi("11/27/2019")

defmodule A do
  @after_compile __MODULE__

  def __after_compile__(_env, _bc), do: lofa

  def lofa, do: IO.inspect(27)
end
#> 27 immediately