my_if.ex

iex(13)> defmodule MyUtil do
...(13)>   defmacro my_if(test, do: body) do
...(13)>     quote do
...(13)>       if unquote(test), do: unquote(body)
...(13)>     end
...(13)>   end
...(13)> end
{:module, MyUtil,
 <<70, 79, 82, 49, 0, 0, 4, 160, 66, 69, 65, 77, 65, 116, 85, 56, 0, 0, 0, 138,
   0, 0, 0, 15, 13, 69, 108, 105, 120, 105, 114, 46, 77, 121, 85, 116, 105, 108,
   8, 95, 95, 105, 110, 102, 111, 95, 95, ...>>, {:my_if, 2}}
iex(14)> require MyUtil
require MyUtil
MyUtil
iex(15)> MyUtil.my_if true do
...(15)>   IO.puts "Hello!"
...(15)>   42
...(15)> end
Hello!
42
iex(16)> MyUtil.my_if false do
...(16)>   IO.puts "Hello!"
...(16)>   42
...(16)> end
nil

my_when.clj

user> (ns my-util)
nil
my-util> (defmacro my-when [test & body]
           `(if ~test
              (do ~@body)))
#'my-util/my-when
my-util> (my-when true
           (println "Hello!")
           42)
Hello!
42
my-util> (my-when false
           (println "Hello!")
           42)
nil