;; The first three lines of this file were inserted by DrRacket. They record metadata
;; about the language level of this file in a form that our tools can easily process.
#reader(lib "htdp-intermediate-lambda-reader.ss" "lang")((modname svolgimento_lez_06) (read-case-sensitive #t) (teachpacks ()) (htdp-settings #(#t constructor repeating-decimal #f #t none #f ())))
;(define (mypow n m)
;  (if (eq? m 0) 1
;      (* n (mypow n (- m 1)))
;  )
;)

(define (amypow n m a)
  (if (eq? m 0) a
      (amypow n (- m 1) (* a n))
  )
)

(define (mypow n m)
  (amypow n m 1)
)

(define (mfirst l) (car l))
(define (msecond l) (cadr l))

; prima versione even_odd_split: gestione completamente esplicita
(define (even_odd_split l)
  (cond
    ( (null? l) (list '() '()) )
    ( (even? (car l)) 
         (list
          (cons (car l) (mfirst (even_odd_split (cdr l))))
          (msecond (even_odd_split (cdr l)))
         )
    )
    ( else
         (list
          (mfirst (even_odd_split (cdr l)))
          (cons (car l) (msecond (even_odd_split (cdr l))))
         )
    )
  )
)
      
; seconda versione: utilizzo di let per semplificare codice e calcolo
(define (even_odd_split2 l)
  (if (null? l) (list '() '())
    (let
        (
         [res (even_odd_split2 (cdr l))]
         [h (car l)]
         )
        ( if (even? h) 
             (list (cons h (mfirst res) ) (msecond res))
             (list (mfirst res) (cons h (msecond res)))           
         )
    )
  )
)

; terza versione: utilizzo di filter (NB filter è già definita in scheme)
(define (mfilter fn l)
  (cond
    ((null? l) '())
    ((fn (car l)) (cons (car l) (mfilter fn (cdr l))) )
    ( else (mfilter fn (cdr l)))
  )
)

(define (even_odd_split3 l)
  (list (mfilter even? l) (mfilter odd? l))
)