How to define a macro correctly?

[Johan Andersson]

Hey,

I want to create a macro that sets a variable value and then executes body. I know how to solve it, but I want to know which way is the best (more correct). I came up with these solutions:

a)

(defmacro mac (&rest body)

  `(progn

     (setq var t)

     ,@body))

b)

(defmacro mac (&rest body)

  (setq var t)

  `(progn ,@body))

c)

(defmacro mac (&rest body)

  (cons 'progn (cons (list 'setq 'var t) body)))

I noticed that (using macroexpand) macro a and c expands to the same list. b however sets the variable in the macro and then only return the list body. What does that mean exactly, that I set the variable in the macro and do not return it as a list?

What way is the best? Or is there some other way that is better?

Thanks!