Enum with lots of sugar

gistfile1.ex

defmodule Enex do
  defmacro map enum, clauses do
    fnc = {:fn, [], [clauses]}
    quote do: Enum.map(unquote(enum), unquote(fnc))
  end

  defmacro reduce enum, acc, clauses do
    fnc = {:fn, [], [clauses]}
    quote do: Enum.reduce(unquote(enum), unquote(acc), unquote(fnc))
  end

  @skip :"__FMAP^SKIP__"

  defmacro fmap enum, clauses do
    {:"->", meta, forms} = clauses[:do]
    skip_clause = {[{:_, [], nil}], @skip}
    clauses     = [do: {:"->", meta, forms ++ [skip_clause]}]
    fnc         = {:fn, [], [clauses]}
    
    fmap_quote(enum, fnc)
  end

  defmacro freduce enum, acc, clauses do
    {:"->", meta, forms} = clauses[:do]
    skip_clause = {[{:_, [], nil}, {:_, [], nil}], @skip} 
    clauses     = [do: {:"->", meta, forms ++ [skip_clause]}]
    fnc         = {:fn, [], [clauses]}
    
    freduce_quote(enum, fnc, acc)
  end

  defmacro select head, opts, block // [] do
    match =
      case head do
        {:when, _, [m|_]} -> m
        _                 -> head
      end
    enum          = opts[:from]
    do_block      = block[:do] || opts[:do] || match
    select_clause = {[head], do_block}
    skip_clause   = {[{:_, [], nil}], @skip}
    clauses       = [do: {:"->", [], [select_clause, skip_clause]}]
    fnc           = {:fn, [], [clauses]}
 
    fmap_quote(enum, fnc)
  end

  defp fmap_quote enum, fnc do
    quote do
      pick =
        fn(x, acc) ->
            case unquote(fnc).(x) do
              unquote(@skip) -> acc
              x              -> [x|acc] 
            end 
        end
      Enum.reduce(unquote(enum), [], pick)
      |> Enum.reverse
    end
  end

  defp freduce_quote enum, fnc, acc do
    quote do
      pick =
        fn(x, acc) ->
            case unquote(fnc).(x, acc) do
              unquote(@skip) -> acc
              new_acc        -> new_acc 
            end 
        end
      Enum.reduce(unquote(enum), unquote(acc), pick)
    end
  end
end