A student's question

My teacher keeps drilling into our collective heads that using the break command is harmful, and that if we wish to terminate a loop early it would be far better to create a boolean variable, set it to 0, and add a condition to the head of the loop, and set the boolean variable to 1 when a break is needed. Note that this way you actually have to check this every single loop (where it is not needed almost every time) as well as waste a command to reset the boolean in case it was set to true.

Is there a reason to this?

>>93
CLISP has its own non-standard extensions, SBCL has its own non-standard extensions...
...but only Scheme/Racket manages to make a whole new language from extensions!

>>95
Macro in LISP.

(defmacro aif (cond then else)
  `(let ((it ,cond))
     (if it ,then ,else)))

"Macro" in Scheme/Racket.

#lang racket
(require racket/stxparam)
 
(define-syntax-parameter it (lambda (stx) (raise-syntax-error 'anaphora "missed context" stx)))
 
(define-syntax-rule (aif cond then else)
  (let ([temp cond])
    (syntax-parameterize ([it (make-rename-transformer #`temp)])
                         (if temp then else))))