skipped? = #t can only arise if some struct type in the hierarchy is opaque, which would mean struct? returns #f. If you only care about types that satisfy struct?, you should be able to safely ignore skipped?, if I understand it correctly.
Carl Eastlund On Sat, Jan 25, 2014 at 6:07 PM, Greg Hendershott <greghendersh...@gmail.com > wrote: > > flaw: If an immutable struct is derived from a mutable one, my > > predicate will (as written) incorrectly report it as immutable. > > Instead I need to walk the chain of super-types, and check that all > > are immutable. I'll work on this more... > > Here's where I ended up for now. > > Although I don't understand how/when/why skipped? = #t would arise, > I'm pretty sure that if it does arise, I can't make any assertion > about immutability and should err on the side of saying "no". > > Will sleep on this. Would welcome feedback if anyone has any. > > ;; As documented, `immutable?` does not work with `struct`s. Define a > ;; predicate that does: > (define (immutable-struct? v) > (define-values (st skipped?) (struct-info v)) > (and (not skipped?) ;unless most-specific type, can't assert immutability > (immutable-struct-type? st))) > > (define (immutable-struct-type? st) > (define-values (name init-field-cnt auto-field-cnt > accessor-proc mutator-proc > immutable-k-list > super-type skipped?) (struct-type-info st)) > ;; A struct-type is immutable if all its fields are immutable, AND > ;; all its super struct-types are immutable. > (and (not skipped?) ;unless most-specific type, can't assert immutability > (= (+ init-field-cnt auto-field-cnt) > (length immutable-k-list)) > (or (not super-type) > (immutable-struct-type? super-type)))) > > (module+ test > (struct mutable (fld) #:mutable #:transparent) > (define m (mutable 0)) > (check-false (immutable-struct? m)) > > (struct mutable:immutable mutable (fld2) #:transparent) > (define m:i (mutable:immutable 0 1)) > (check-false (immutable-struct? m:i)) > > (struct immutable (fld) #:transparent) > (define i (immutable 0)) > (check-true (immutable-struct? i)) > > (struct immutable:immutable immutable (fld2) #:transparent) > (define i:i (immutable:immutable 0 1)) > (check-true (immutable-struct? i:i))) >
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