;;; Alef Lazily Evaluates Functions
;;; (C) 2008-2009 Dr. Gergo ERDI <http://gergo.erdi.hu/>

(in-package :alef)

(defparameter *library-decls*
  '(; Arithmetics
    (declare/virtual (+ a) () (a a a))
    (declare/virtual (- a) () (a a a))
    (declare/virtual (* a) () (a a a))
    (declare/virtual (/ a) () (a a a))

    (declare/virtual (= a) () (a a bool))
    
    (declare/virtual (< a) () (a a bool))
    
    ; Conversion to string
    (declare/virtual (show a) () (a string))))

(defparameter *library-native*
  '((define/override (+ int) (x y) (+/int x y))
    (define/override (- int) (x y) (-/int x y))
    (define/override (* int) (x y) (*/int x y))
    (define/override (/ int) (x y) (//int x y))
    (define/override (= int) (x y) (=/int x y))
    (define/override (< int) (x y) (</int x y))

    (define/override (show int) (x) (show/int x))
    (define/override (show string) (x) x)))

(defparameter *library*
  `(,@*library-decls*
    ,@*library-native*

    (deftype bool () true false)
    
    (define and (false _) false)
    (define and (true  x) x)
   
    (define or (true  _) true)
    (define or (false x) x)
    
    (define not (true)  false)
    (define not (false) true)   
    
    (define if (true then else)  then)
    (define if (false then else) else)
    
    (define <= (x y) (or (= x y) (< x y)))
    (define > (x y) (< y x))
    (define >= (x y) (<= y x))
    
    (deftype list (t)
      nil
      (cons t (list t)))
    
    (define length (nil)         0)
    (define length ((cons _ xs)) (+ 1 (length xs)))
    
    (define take (0 _)           nil)
    (define take (_ nil)         nil)
    (define take (k (cons x xs)) (cons x (take (- k 1) xs)))
    
    (define drop (0 xs) xs)
    (define drop (k nil) nil)
    (define drop (k (cons x xs)) (drop (- k 1) xs))
    
    (define map (f nil)         nil)
    (define map (f (cons x xs)) (cons (f x) (map f xs)))
    
    (define filter (p nil) nil)
    (define filter (p (cons x xs)) (if (p x) (cons x (filter p xs)) (filter p xs)))
    
    (define append (xs          nil) xs)
    (define append (nil         ys)  ys)
    (define append ((cons x xs) ys)  (cons x (append xs ys)))
    
    (define concat (nil) nil)
    (define concat ((cons x xs)) (append x (concat xs)))
    
    (define show/list* (nil _) ("]"))
    (define show/list* (l false) (+/string "," (show/list* l true)))   
    (define show/list* ((cons x xs) true) (+/string (show x) (show/list* xs false)))
    
    (define show/list (l) (+/string "[" (show/list* l true)))

    (define/override (show list) (l) (show/list l))))