#;42> (define sixteen (<Just> 16))
#;43> (define div2 (lambda (n) (if (even? n) (<Just> (/ n 2)) <Nothing>)))
#;44> (from-just (>>= sixteen div2 div2 div2))
2
#;45> (from-just (>>= (<Just> 3) div2 div2 div2))

Error: from-just called on <Nothing>