[plt-scheme] HTDP 12.4.2

You have changed the specs on us :-)

On Jun 22, 2006, at 2:06 PM, wooks wooks wrote:

>
> At 4:43 AM +0100 6/22/06, wooks wooks wrote:
>> LOL. Ok I've been rumbled.
>
> Gee, I hope not :-)
>
>> I'll start all over again the way I've been told and await the light 
>> bulb moment.
>
> "Awaiting the light bulb moment" is what you've BEEN doing; we suggest 
> instead following a systematic procedure that doesn't rely on 
> unpredictable light bulbs.
> --
>
> I meant the light bulb moment as in true understanding why one should 
> stick to the systematic procedure (something more than thats how they 
> told me to do it).
>
> Anyway I'd appreciate some input on this revised effort (most 
> particularly my template) before going to the next stage.
>
> ;CONTRACT
> ;insertEverywhere : symbol ('a - 'z) list-of-words - list of words
> ;returns a list of words constructed by interpersing symbol before, 
> after and between each letter, of
> ;each word in the list-of-words
> ;
> ;EXAMPLES
> ;(insertEverywhere 'd
> ;  (cons (cons 'e (cons 'r empty))
> ;    (cons (cons 'r (cons 'e empty))
> ;      empty))) gives
> ; (list (list 'd 'e 'r)
> ;       (list 'e 'd 'r)
> ;       (list 'e 'r 'd)
> ;       (list 'd 'r 'e)
> ;       (list 'r 'd 'e)
> ;       (list 'r 'e 'd))
>
> ;TEMPLATE
> ;(define (insertEverywhere sym alow)
> ;  (cond
> ;    [(empty? alow) ...sym....]
> ;    [else ...sym...(first (first alow)) .....
> ;          ..sym....(rest (first alow)) .....
> ;          .....(insertEverywhere sym (rest alow)).....]
> ;   )
> ;)

Good. The rest (no pun intended) is obvious for this one:

(define (iE letter alow)
   (cond [(empty? alow) empty]
         [else (??????? (iE/word letter alow) (iE letter (rest alow))]))

iE/word is an entry on your wish list:

;; iE/word : letter word -> list-of-words
;; insert a letter at beginning, end, and between the letters of a word

????? is up to you. --- Matthias





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