;; The first three lines of this file were inserted by DrScheme. They record metadata
;; about the language level of this file in a form that our tools can easily process.
#reader(lib "htdp-advanced-reader.ss" "lang")((modname lect03c) (read-case-sensitive #t) (teachpacks ((lib "world.ss" "teachpack" "htdp"))) (htdp-settings #(#t constructor repeating-decimal #t #t none #f ((lib "world.ss" "teachpack" "htdp")))))
#|
The steps of design recipe (taken from How to Design Programs).
1. Data Def'n
2. Examples of Data
3. Template for functions handling the data
4a Write function header
 b Write function comments
 c Write test cases
 d Write function body
   i.   a cond line for each variant of union data
   ii.  pull out fields for each line handling a struct
   iii. add natural-recursion call, if present.
5. run tests

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;;Compare to the data defn for natnums:
; Data def'n:
; A natnum is:
;   - 0, or
;   - (add1 [natnum])

;What would a template look like for natnums?
;Did our code for ! follow the template?  Yes!






;;;; The robo-rally game:

;  A simple robot game has robots follow instructions like "walk 2,
;  turn left, walk 4, walk 6, turn right ...".  We want a data
;  definition to capture this.;

  A list-of-num-and-sym is
    - empty, or
    - (cons number list-of-num-and-sym)
    - (cons symbol list-of-num-and-sym)


(cons 1 (cons 'left (cons 5 (cons 'right empty))))
;Alternate syntax:
(list 1 'left 5 'right)

;  Make sure to develop a cond with three clauses in cond, not 2 --

  ;; total-steps : list-of-num-and-sym -> number
  ;; produces the sum of all the numbers in the list





#|
Trees.

abe   mona     jackie 
homer          marge
bart

(define abe (make-person "Abe" 1920 'blue 'unknown 'unknown))
(define mona (make-person "Mona" 1929 'brown 'unknown 'unkown))
(define jackie (make-person "Jackie" 1926 'brown 'unknown 'unknown))
(define marge (make-person "Marge" 1956 'blue jackie 'unknown))
(define homer (make-person "Homer" 1955 'brown mona abe))
(define bart (make-person "Bart" 1979 'brown homer marge))


contains-name?
count-oldies
find-blue-eyes
find-blue-eyed-orphans
find-oldies
.... generalized find!
find-long-names
find-named-for-ancestor
find-time-travelers: somebody whose has an ancestor whose birth-year
   is later than their own!
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#|
Quote.
Sexpr.
  (see GlobalPreferences.plist.orig

build-list
write filter (passing in a list)
  map, filter, fold(reduce); 
writing loop;

Accumulator versions:
; sum-accum
; reverse : (-> (list-of any) (list-of any))

This follows from the template, although we need a helper:


; add-at-end : (-> (list-of animal) animal (list-of animal))
; Given a list of animals and another animal,
; Return a list containing all the listed 
; 
(define (add-at-end zoo newguy)
  ...)


What is running time?  Memory usage?


Accumulators; tail-recursion.
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