On Jul 1, 2012, at 4:17 PM, Sean Kemplay wrote:
> Looking back, I am wondering if my solution is a bit of a cheat -
> specifically :
>
> (define (insert-everwhere/in-one-word s word)
> (make-words s word word))
It's not a cheat, it's wrong. I did you a favor and worked out a failing test
case. See below.
On Jul 1, 2012, at 6:46 PM, Dave Yrueta wrote:
> Try working through this exercise by systematically applying the design
> recipe. That is, take the time to make your data definitions explicit, and
> begin the definition of each helper function with a contract, purpose
> statement, and template. In my opinion, more than any other exercise in
> HtDP, the solution to this exercise relies on paying very close attention to
> how the data definitions, function contracts and function templates interact.
> If you allow the data definitions to shape the function templates, and are
> rigorous about ensuring the function designs conform to their contracts, the
> solution should fall into place.
The above is the best advice the list can give you. -- Matthias
;; World = [Listof Letter] ;; see chapter IV
;; Letter = Symbol
;; Letter Word -> [Listof Word]
;; the function says: insert _s_ in all positions in _word_
(check-expect (insert-everwhere/in-one-word 'a '(w o))
'((a w o) (w a o) (w o a)))
(check-expect (insert-everwhere/in-one-word 'a '(w w o))
'((a w w o) (w a w o) (w w a o) (w w o a)))
(define (insert-everwhere/in-one-word s word)
(make-words s word word))
;; Letter Word Word -> [Listof Word]
;; insert _s_ in all positions in _word2_ using _word1_ as a list of insertion
points
;; intended usage: (make-words letter word word) i.e. word1 = word2 initially
(check-expect (make-words 'a '(w o) '(w o)) '((a w o) (w a o) (w o a)))
(check-expect (make-words 'a '(w w o) '(w w o)) '((a w w o) (w a w o) (w w a o)
(w w o a)))
(define (make-words s word1 word2)
(cond
[(empty? word1) (cons (append word2 (cons s empty)) empty)]
[else (cons (insert-symbol s (first word1) word2) (make-words s (cdr word1)
word2))]))
;; Letter Letter Word -> Word
;; add _new_ in front of each occurrence of _old_ in _word_
(check-expect (insert-symbol 'a 'b '(c d e)) '(c d e)) ;; running in BSL with ..
(check-expect (insert-symbol 'a 'b '(b o b)) '(a b o a b))
(define (insert-symbol new old word)
(cond
[(empty? word) empty]
[(symbol=? (first word) old) (cons new (cons old (insert-symbol new old
(rest word))))]
[else (cons (first word) (insert-symbol new old (rest word)))]))
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