On Fri, Feb 15, 2019 at 12:18 AM David Storrs <david.sto...@gmail.com> wrote: > > On Thu, Feb 14, 2019 at 9:08 PM Robby Findler > <ro...@eecs.northwestern.edu> 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 <chris...@gmail.com> > > 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 > >> > >> > >> -- > >> You received this message because you are subscribed to the Google Groups > >> "Racket Users" group. > >> To unsubscribe from this group and stop receiving emails from it, send an > >> email to racket-users+unsubscr...@googlegroups.com. > >> For more options, visit https://groups.google.com/d/optout. > > > > -- > > You received this message because you are subscribed to the Google Groups > > "Racket Users" group. > > To unsubscribe from this group and stop receiving emails from it, send an > > email to racket-users+unsubscr...@googlegroups.com. > > For more options, visit https://groups.google.com/d/optout. -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
