$re = '/\(\s*define\s*(\(.*?\))/ms';
$str = '#lang sicp
(define (square x) (* x x))
(define (average x y) (/ (+ x y) 2))
; using block scope
(define (sqrt x)
; x is always the same -- "4" or whatever we pass to it, so we don\'t need that
; in every single function that we define, we can just inherit it from above.
(define (improve guess) (average guess (/ x guess)))
(define (good-enough? guess) (< (abs (- (square guess) x)) 0.001 ))
(define (sqrt-iter guess) (if (good-enough? guess) guess (sqrt-iter (improve guess))))
(sqrt-iter 1.0)
)
(sqrt 4)
(define (inc x) (+ x 1))
(define (dec x) (- x 1))
';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php