#lang racket

;; CSE 413 Au12 lecture 8 sample code

;; return a function that will add n to all of the elements of a list
(define addn-to-list
  (lambda (n)
    (lambda (lst) (map (lambda (x) (+ n x)) lst))))

; ((addn-to-list n) '(1 2 3 4))
; (define add3-to-list (addn-to-list 3))
; (add3-to-list '(1 2 3 4))


;; filter
(define filter413
  (lambda (f lst)
    (cond ((null? lst) '())
          ((f (car lst)) (cons (car lst) (filter413 f (cdr lst))))
          (else (filter413 f (cdr lst))))))

;; return a list with all elements x such that lo<=x<=hi
(define filterinrange
  (lambda (lo hi lst)
    (filter413 (lambda (n) (and (>= n lo) (<= n hi))) lst)))
; (filterinrange 3 5 '(1 2 3 4 5 6))

;; Curried functions revisited

;; curried addition function
(define plus
  (lambda (x)
    (lambda (y) (+ x y))))

;; curried higher-order functions

;; curried map
(define cmap
  (lambda (f)
    (lambda (lst) (map f lst))))

;; curried filter - return a function that uses function f to filter a list
(define cfilter
  (lambda (f) (lambda (lst) (filter f lst))))

;; return elements of a list in the range lo to hi
(define rangefilter
  (lambda (lo hi)
    (cfilter (lambda (n) (and (>= n lo) (<= n hi))))))

; ((rangefilter 3 5) '(1 2 3 4 5 6 7)
; (define range35filter (rangefilter 3 5))
; (range35filter '(1 2 3 4 5 6 7))

;; test functions
(define (sqr n) (* n n))
(define (incr n) (+ 1 n))
(define (dbl n) (+ n n))

;; function composition - return f o g
(define compose
  (lambda (f g)
    (lambda (x) (f (g x)))))

;; ((compose sqr incr) 4)
;; ((compose incr sqr) 4)
;; (define sqrincr (compose sqr incr))