====== Macros ======

Let's see simple example, without explaining the syntax of macro definition:

<code lisp>
>(defmacro do3times (a) `(progn ,a ,a ,a nil))   ; special form DEFMACRO defines macro 
DO3TIMES
>(do3times (print "Hello"))     ; function PRINT will be called three times
"Hello"
"Hello"
"Hello"
NIL
</code>

When the first symbol ''DO3TIMES'' is recognized as a name of a macro, the form will be treated as macro-expansion form. In principle it means that two-step evaluation will happen. First the non-evaluated argument ''(print "Hello")'' is submitted to the procedure we defined by ''DEFMACRO'' that will decide what to do with it - macro can evaluate, reorder, restructure the forms - and will return new piece of code. In the second step, the code is evaled.
The first step is called //macro expansion// and can be examined with a function ''MACROEXPAND'' 

<code lisp>
>(macroexpand '(do3times (print "Hello")))   ; we expand the previously called command
(PROGN (PRINT "Hello") (PRINT "Hello") (PRINT "Hello") NIL)    ; this is the returned code
T
</code>