[racket] on contract violation after adding 1471 strings to a BST

Warning: you switched from a teaching language to full Racket. 
The former would have caught this mistake, which is why we 
designed them for HtDP. Racket is for grown-up parenthesis 
eaters -- who want the behavior of cond that you just experienced, 
or so I am told. -- Matthias






On Aug 5, 2014, at 4:25 PM, Daniel Bastos <dbastos at toledo.com> wrote:

> On Tue, Aug 5, 2014 at 5:06 PM, Jens Axel Søgaard <jensaxel at soegaard.net> wrote:
> What happens in create-bst-word, when the word to inserted is the same
> as (node-word bst) ?
> 
> Aha! I see. It returns void because there is no case for when the string is equal. 
> 
> > (void? (create-bst-word (create-bst-word false "dan") "dan"))
> #t
> 
> I patched it with an else-case now.
> 
> (define (create-bst-word bst str)
>   (cond
>    ((false? bst)
>     (make-node str false false))
>    ((string<? str (node-word bst)) ;; insert at the left
>     (make-node (node-word bst)
>                (create-bst-word (node-left bst) str)
>                (node-right bst)))
>    ((string>? str (node-word bst)) ;; insert at the right
>     (make-node (node-word bst)
>                (node-left bst)
>                (create-bst-word (node-right bst) str)))
>    (else (make-node (node-word bst)
>                     (node-left bst)
>                     (node-right bst)))))
> 
> > (void? (create-bst-word (create-bst-word false "dan") "dan"))
> #f
> 
> Thank you.
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