Re: Contracts question on structs

I believe it should be since bst/c is supposed to be a contract. Also I
noticed the docs at
https://docs.racket-lang.org/reference/data-structure-contracts.html show a
similar example:

; bst-between : number number -> contract
; builds a contract for binary search trees
; whose values are between low and high
(define (bst-between/c low high)
  (or/c null?
        (struct/dc node [val (between/c low high)]
                        [left (val) #:lazy (bst-between/c low val)]
                        [right (val) #:lazy (bst-between/c val high)])))


On Fri, Feb 15, 2019 at 1:31 AM David Storrs <[email protected]> wrote:

> On Fri, Feb 15, 2019 at 12:18 AM David Storrs <[email protected]>
> wrote:
> >
> > On Thu, Feb 14, 2019 at 9:08 PM Robby Findler
> > <[email protected]> wrote:
> > >
> > > This is what struct/dc is for. Let me know if the docs let you down!
> > >
> > > Robby
> >
> > This is good to hear about, because I'm actually in the middle of
> > writing something that it will help with.  Thanks, Robby.
> >
> > One question:  Is there a typo in the example code or am I missing
> something?
> >
> > (struct bt (val left right))
> > (define (bst/c lo hi)
> > (or/c #f
> > (struct/dc bt
> > [val (between/c lo hi)]
> > [left (val) #:lazy (bst lo val)]                   ; should that be (bt
> lo val)?
> > [right (val) #:lazy (bst val hi)])))             ; and this be (bt val
> hi) ?
>
> Ugh.  I hate it when I make significant typos in code questions.  I
> should have asked if it was supposed to (bst/c lo val) and (bst/c val
> hi). (i.e., is there a missing /c in the code?)  If not, where is bst
> defined?
>
> >
> > Also, am I correct that the contract is not actually attached to the
> > bt structure at this point?  That's a thing that would be done
> > elsewhere, probably in the provide statement.  Yes?
> >
> > >
> > > On Thu, Feb 14, 2019 at 7:57 PM Chris GauthierDickey <
> [email protected]> wrote:
> > >>
> > >> I'm wondering if it's possible to have a contract for a struct that
> only allows certain kinds of initializations. For example, I have this:
> > >>
> > >> (provide (contract-out
> > >>           [struct Result ((name (or/c Temp? Label?)) (global?
> boolean?) (value (or/c VarValue? #f)))]))
> > >>
> > >> But it's too general. What I'd really like to have is a contract that
> combines them like an or/c (I can see what this would cause problems, just
> wondering if there's a clever way around it):
> > >> (provide (contract-out
> > >>           [or/c (struct Result ((name Temp?) (global? #f) (value
> (or/c VarValue? #f))))
> > >>                 (struct Result ((name Label?) (global? boolean?)
> (value (or/c (VarValue #f)))))]))
> > >>
> > >> In this case, if name is Temp? then global? has to be #f. If name is
> Label? then global? can be #t or #f. I'd like to use struct cause it
> provides all the contracts for accessors and such. Note, I can use a
> #:guard on the struct, but wondered if it was possible to do something
> along these lines with a contract.
> > >>
> > >> Thanks!
> > >> Chris
> > >>
> > >>
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