Can you execute multiple statements in an "if" statement?

Question

This is my function:

(defun MyFunction(input)   (let ((NEWNUM (find input num)))     (if (find input num)              //if this        (setq num NEWNUM) (FUNCT2)      //then execute both of these     (list 'not found))))              //else output this 

So after the if statement I want to be able to execute (setq num NEWNUM) followed by (FUNCT2) in order to set a new variable and then call a function. Any ideas on how to do this?

Answer 1

To do several things in sequence, you want progn.

(defun MyFunction(input)   (let ((NEWNUM (find input num)))     (if (find input num)              //if this        (progn          (setq num NEWNUM)         (FUNCT2))      //then execute both of these     (list 'not found))))              //else output this 

Answer 2

When your if is 'one-armed', as they call it (that is, it contains no else branch), it's typically easier and more idiomatic to use when and unless: http://www.cs.cmu.edu/Groups/AI/html/hyperspec/HyperSpec/Body/mac_whencm_unless.html

When you call (when pred x y ... z), it will just evaluate x y z sequentially if pred is true. unless behaves similarly when pred is NIL. x y z can represent any number of statements from one upwards. Thus:

(when pred (thunk)) 

is just the same as

(if pred (thunk)) 

Some people say when and unless should always be used for 'one-armed-ifs' because of clarity.

Edit: Your thread gave me an idea. This macro:

(defmacro if/seq (cond then else)   `(if ,cond (progn ,@then) (progn ,@else))) 

should enable this:

(if/seq (find input num)              //if this        ((setq num NEWNUM) (FUNCT2))      //then execute both of these     ((list 'not found)))))  

So the general format is:

(if/seq *condition* (x y ... z) (a b ... c)) 

Depending on the condition, it evaluates all of the subforms in the first or second, but only returns the last.