Hi Nick! Interesting observation. I tried the same thing with immutable hash tables in place of sets (just mapping each element to #t), and got the same results. So I don't think the set implementation is the culprit here. I suspect the built-in equality and/or hash functions for either immutable hash tables, or transparent structs, or both, doesn't properly handle circular values.
Carl Eastlund On Fri, Jul 26, 2013 at 5:25 PM, Nicholas Labich <[email protected]> wrote: > I'm running into what I find to be surprising behavior with circular > structures (vertices of a simple graph). > > Graphically (see code below to reproduce): > 0 --> 1 ;; no problem > 2-+ ;; also no problem > ^-+ > > But when I try to add an edge between 0 and 2, I hit an infinite loop at > line 88 of racket/set.rkt (in 5.3.3) or line 447 of > racket/private/set-types.rkt (in the latest 5.90.0.2), both of which are > the hash-proc for set's gen:equal+hash. > > Is this the expected behavior (after all, OCaml makes no guarantee of > termination for (=) on circular data)? I'm surprised that the self-edge on > 2 doesn't result in the same. I've also tried to reproduce the same using > `shared', but I'm assuming I still misunderstand its functionality because > the result is not quite what I expect it to be. > > Any insight would be much appreciated. > > Nick > > Welcome to Racket v5.90.0.2. > > (struct vertex (value preds succs) #:mutable #:transparent) > > (define v0 (vertex 0 (set) (set))) > > (define v1 (vertex 1 (set) (set))) > > (set-vertex-succs! v0 (set v1)) > > (set-vertex-preds! v1 (set v0)) ;; 0 --> 1 > > (equal? v0 (set-first (vertex-preds v1))) > #t > > (define v2 (vertex 2 (set) (set))) > > (set-vertex-preds! v2 (set v2)) ;; 2--+ > > (set-vertex-succs! v2 (set v2)) ;; ^--+ > > v2 > #0=(vertex 2 (set #0#) (set #0#)) > ;; try to add the already existing set > > (set-vertex-succs! v0 (set-add (vertex-succs v0) v2)) ;; loops and loops > C-c C-c^Cuser break > context...: > .../racket/collects/racket/private/set-types.rkt:447:3: hash-proc > .../racket/collects/racket/private/set-types.rkt:447:3: hash-proc > .../racket/collects/racket/private/set-types.rkt:447:3: hash-proc > .../racket/collects/racket/private/set-types.rkt:447:3: hash-proc... > ;; try to make a new set instead > > (set-vertex-succs! v0 (set v1 v2)) > C-c C-c^Cuser break > context...: > .../racket/collects/racket/private/set-types.rkt:447:3: hash-proc > .../racket/collects/racket/private/set-types.rkt:447:3: hash-proc > .../racket/collects/racket/private/set-types.rkt:447:3: hash-proc > .../racket/collects/racket/private/set-types.rkt:447:3: hash-proc... > > > (shared ([v0 (vertex 0 (set) succs0)] > [v1 (vertex 1 preds1 (set))] > [v2 (vertex 2 preds2 succs2)] > [succs0 (set v1 v2)] > [preds1 (set v0)] > [preds2 (set v0 v2)] > [succs2 (set v2)]) > (values v0 v1 v2)) > (vertex 0 (set) (set #0=(vertex 2 (set #0#) (set #0#)))) > (vertex 1 (set (vertex 0 (set) (set #0=(vertex 2 (set #0#) (set #0#))))) > (set)) > #0=(vertex 2 (set #0#) (set #0#)) > ;; I must be using `shared' incorrectly... > > ____________________ > Racket Users list: > http://lists.racket-lang.org/users > >
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