;; 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 lect04c-v2) (read-case-sensitive #t) (teachpacks ((lib "universe.ss" "teachpack" "2htdp") (lib "image.ss" "teachpack" "2htdp"))) (htdp-settings #(#t constructor repeating-decimal #f #t none #f ((lib "universe.ss" "teachpack" "2htdp") (lib "image.ss" "teachpack" "2htdp")))))
#|
hw04 discuss:

  draw-astrs by template;
  then, as tail-recursive
  
  design recipe:
    http://htdp.org/2003-09-26/Book/curriculum-Z-H-13.html#node_sec_9.4
  tail-recursion; using an accumulator.
  Exercise: write 'min' using an accumulator; first in Java, then in tail-recursive racket


review/remember:
  lambda


;;;;;;;;;; for next week:
  First-order functions: 
     Hey, check out 'sort':  
       sort strings alphabetically;
         (sort string<=? (list "hi", "bye", "Zoomba!"))
       sort by alphbetical-case-independent
         (sort (lambda (s1 s2) (string<=? (to-upcase s1) (to-upcase s2))) 
               (list "hi", "bye", "Zoomba!"))
         (list "hi", "bye", "Zoomba!"))
       alphabetical-igorning "A ", "The ":
       
     write filter-evens (think about: filter-odds, filter-primes, filter-long-strings, ...)

     write my-map (by design recipe)

     What about fold ?

     
     ... grammars and parsing ...

|#

(require mzlib/pregexp)
(define (has-prefix? pre str)
  (cons? (pregexp-match (string-append "^" pre) str)))
(define (drop-prefix pre str)
  (substring str (string-length pre)))
(check-expect (drop-prefix "abc" "abcdef") "def")









(define (help-min_v2 data min-so-far)
  (cond [(empty? data) min-so-far]
        [(cons? data) (min_v2 (rest data) 
                              (min-of-two (first data) min-so-far))]))

; min_v2 :  cons? -> number
(define (min_v2 nums)
  (help-min_v2 (rest nums) (first nums)))
  
  
(define (min-of-two x y)
  (if (< x y)
      x
      y))