TAKE in Scheme, CL and Miranda

take.lisp

; page 13, Ralf Hinze, Einführung in die funktionale Programmierung mit Miranda

#|

take' 0 x = []
take' (n+1) [] = []
take' (n+1) (a:x) = a : take' n x

; The ugly Scheme version in the book
(define take
   (lambda (n x)
      (cond
         ((zero? n) '())
         (else (cond
                  ((null? x) '())
                  (else (cons (car x)
                              (take (-1+ n) (cdr x))))
       ))
)))

; easily better written as
(define (take n x)
  (cond
     ((zero? n) '())
     ((null? x) '())
     (else (cons (car x)
                 (take (-1+ n) (cdr x))))))

|#


(defun take (n x)
  (if (or (zerop n) (null x))
      '()
    (cons (first x)
          (take (1- n) (rest x)))))

(defun take (n x)
  (loop repeat n
        while x
        collect (pop x)))

(defun take (n x)
  (loop for e in x
        repeat n
        collect e))