(assert= 'hello' 'hello')
(assert (not (eq? 'bim' 'bam')))

(assert= false (empty? 'coucou'))
(assert= true (empty? ''))

(assert= 'e' (ref 'hello' 1))
(assert= 5 (len 'hello'))

(assert= 'aaa' (dup 'a' 3))
(assert= 'abcdefg' (cat 'abc' 'def' 'g'))