In Racket and other Schemes parens and square brackets are interchangeable. The Racket style guide suggests to use square brackets in let- or cond-like expressi

In Racket and other Schemes parens and square brackets are interchangeable. The Racket style guide suggests to use square brackets in let- or cond-like expression, or generally any expression with a list of lists of fixed length that are not supposed to be evaluated. The expression you posted would become like this: (do ([i 1 (+ i 1)]) ((> i 100)) (display (cond [(= 0 (modulo i 15)) "FizzBuzz"] [(= 0 (modulo i 3)) "Fizz"] [(= 0 (modulo i 5)) "Buzz"] [else i])) (newline)) I personally think this helps a lot with the problem of parsing s-expressions visually.