Modified run-length encoding

	;; P11 (*) Modified run-length encoding.
	;; Modify the result of problem P10 in such a way that if an element has no duplicates it is simply copied into the result list. Only elements with duplicates are transferred as (N E) lists.
	;; Example:
	;; * (encode-modified '(a a a a b c c a a d e e e e))
	;; ((4 A) B (2 C) (2 A) D (4 E))
	(require srfi/1)
	(define (encode lst)
	(let loop ((lst lst) (acc '()))
	(if (null? lst)
	(reverse acc)
	(loop (strip lst)
	(cons
	(let ((head (car lst))
	(len (length (picks lst))))
	(if (= len 1)
	head
	`(,len ,head)))
	acc)))))
	(define-syntax define-encode-aux
	(syntax-rules ()
	((_ name proc)
	(define (name lst)
	(let ((head (car lst)))
	(proc (lambda (x)
	(eq? head x)) lst))))))
	;; Using a procedure, take-while, defined in SRFI-1
	(define-encode-aux picks take-while)
	;; Using a procedure, drop-while, defined in SRFI-1
	(define-encode-aux strip drop-while)

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