;;
;; Pretext
;;

(define-module (pretext))
;  #:replace (list-head))

;;
;; Runtime Environment Options
;;
(debug-set! stack (* 2 (expt 10 7)))
(debug-set! depth 200)
(debug-set! maxdepth (expt 10 6))


(define (natural-number? n)
  (and (exact? n)
       (integer? n)  ; 'integer?' does not check for exactness ...
       (> n 0)))

(define-public (repeat n closure)
  "Execute closure n times."
  (if (not (or (natural-number? n) (= n 0)))
      (error "repeat: the parameter n must be an exact natural number or zero.")
      (let loop ((i 0))
        (if (< i n)
          (begin
            (closure)
            (loop (1+ i)))) )))

(define-public from-module @)

(define-public (my-debug . args)
  (for-each (lambda (arg) (display arg))
            args)
  (newline))
;(define-public debug my-debug)

(define-public (my-list-head list n)
  (if (or (null? list) (<= n 0))
      '()
      (cons (car list) (my-list-head (cdr list) (- n 1)))))

(define (my-take list n)
  (if (< n 0)
      (error "take: the parameter n has to be an exact natural number or zero"))
  (cond ((and (not (null? list)) (= n 0)) '())
        ((and (null? list) (not (= n 0)))
         (error "take: argument out of range: n was greater than the length of the list."))
        ((and (not (null? list)) (> n 0))
         (cons (car list)
               (take (cdr list) (- n 1)) ))
        (else
         (error "take: Oh dear, we failed!"))) )