Implement a Basic block/yield with Elixir

Mustafa Turan

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Feb 23, 2017 · 1 min read

With powerful macros, Elixir language allows you to code magic without pain. Sometimes, you might need to run a snippet of code before and after execution of a block of code on several function calls. For instance, you need to measure the time elapsed in code blocks, then Elixir macros will run for help.

defmodule TimeFrame do
  defmacro execute(name, units \\ :micro_seconds, do: yield) do
    quote do
      start = System.monotonic_time(unquote(units))
      result = unquote(yield)
      time_spent = System.monotonic_time(unquote(units)) - start
      IO.puts("Executed #{unquote(name)} in #{time_spent} #{unquote(units)}")
      result
    end
  end
end

Let’s run a piece of code and print automatically how much time was spent.

require TimeFrameresult1 = 
  TimeFrame.execute "ti1" do
    3 + 5 * 912312313123
  end# Executed ti1 in 5 micro_seconds
# 4561561565618result2 = 
  TimeFrame.execute "ti2", :seconds do
    IO.puts("sth")
    3 + 5
  end# sth
# Executed ti2 in 0 seconds
# 8

In case, you need to use the result of executions; ‘result1’ will be assigned to value ‘4561561565618’ and ‘result2’ will be assigned to value ‘8’.

Lastly, if you don’t want to use always ‘unquote’ to access vars inside quote block, you can use ‘bind_quoted’.

Happy coding with ❤!