Ah. Yes, that makes more sense. Thanks. On Sat, Dec 9, 2017 at 3:32 PM, Robby Findler <ro...@eecs.northwestern.edu> wrote: > One hopefully helpful piece of information is that _all_ values in Racket > are structs. So this predicate is telling you that this kind of value is > revealing its inherent "structness" to you or not. > > In this case, the struct isn't transparent so it isn't revealing it. (Just > like cons pairs don't reveal their structs, neither do rational numbers or > procedures, etc.) > > Hopefully this helps the docs make more sense. > > Robby > > On Sat, Dec 9, 2017 at 2:27 PM David Storrs <david.sto...@gmail.com> wrote: >> >> (struct fruit (name color)) >> >> -> (struct? (fruit 'apple 'red)) >> #f >> >> This surprised me. I'm trying to wrap my head around the docs for >> struct? and struct-info? and not having a lot of success. Is there a >> way to simply say "is this a struct of some sort?" >> >> Context: >> >> I'm playing around with structs that contain information about structs >> and I'd like to be able to validate the information that's going in: >> >> (struct field-info (field-name predicate getter setter required? >> default on-update) >> #:guard (lambda (field-name predicate getter setter required? >> default on-update type) >> (define/contract (init-field-info field-name predicate >> getter setter required? default on-update) >> (-> symbol? ; field name >> (-> any/c boolean?) ; predicate >> (-> struct? any/c) ; getter >> (-> struct? struct?) ; setter >> boolean? ; required >> (or/c (not/c procedure?) ; default >> (-> struct? any/c)) >> (-> struct? any/c any) ; on-update >> any ; unchecked return value >> ) >> (when (and required? (not-equal? default >> 'no-default-specified-by-field-info)) >> (raise-arguments-error 'init-field-info >> "Cannot specify a default for a >> required field" >> "default" default)) >> (values field-name predicate getter setter required? >> default on-update)) >> ; >> (init-field-info field-name predicate getter setter >> required? default on-update))) >> >> -- >> 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.
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