Re: case and quoted keys - a misunderstanding

B. Pym wrote:

  (defun read-to-char (c stream)
    (loop for x = (read-char stream nil)
       while x do (when (char= x c) (return t))))

 
How verbose!!  The function can be expressed much more concisely as:
 
     (defun read-to-char (c stream)
       (loop for x = (read-char stream nil)
          while x when (char= x c) return t))
 
or if one doesn't mind the possibility of an extra return value, as:
 
     (defun read-to-char (c stream)
       (ignore-errors (loop when (eql (read-char stream) c) return it))

 
Why is LOOP needed?
 
Scheme:
 
(define (read-to-char c port)
  (let ((r (read-char port)))
    (unless (or (eof-object? r) (eq? c r))
      (read-to-char c port))))

Gauche Scheme

(use srfi-121) ; generators

(define (read-to-char c port)
  (generator-find (is c) (cut  read-char port)))


Given:

(define is
  (case-lambda
    [(x) (lambda(y) (equal? y x))]
    [(pred x) (lambda(y) (pred y x))]
    [(pred key x) (lambda(y) (pred (key y) x))]))