<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div><br></div><div>It looks to me like you can't specify rational sets with shared: </div><div><br></div><div><blockquote type="cite"><div><font class="Apple-style-span" color="#000000">% racket</font></div><div><font class="Apple-style-span" color="#000000">Welcome to Racket v5.90.0.3.</font></div><div><font class="Apple-style-span" color="#000000">> (struct vertex (v s p) #:transparent #:mutable)</font></div><div><font class="Apple-style-span" color="#000000">> (define-values (x y z)</font></div><div><font class="Apple-style-span" color="#000000">    (shared ([v0 (vertex 0 (list) succs0)]</font></div><div><font class="Apple-style-span" color="#000000"><span class="Apple-tab-span" style="white-space:pre"> </span>     [v1 (vertex 1 preds1 (list))]</font></div><div><font class="Apple-style-span" color="#000000"><span class="Apple-tab-span" style="white-space:pre"> </span>     [v2 (vertex 2 preds2 succs2)]</font></div><div><font class="Apple-style-span" color="#000000"><span class="Apple-tab-span" style="white-space:pre"> </span>     [succs0 (list v1 v2)]</font></div><div><font class="Apple-style-span" color="#000000"><span class="Apple-tab-span" style="white-space:pre"> </span>     [preds1 (list v0)]</font></div><div><font class="Apple-style-span" color="#000000"><span class="Apple-tab-span" style="white-space:pre"> </span>     [preds2 (list v0 v2)]</font></div><div><font class="Apple-style-span" color="#000000"><span class="Apple-tab-span" style="white-space:pre"> </span>     [succs2 (list v2)])</font></div><div><font class="Apple-style-span" color="#000000">      (values v0 v1 v2)))</font></div><div><font class="Apple-style-span" color="#000000">> x</font></div><div><font class="Apple-style-span" color="#000000">#0=(vertex 0 '() (list (vertex 1 '(#0#) '()) #1=(vertex 2 '(#0# #1#) '(#1#))))</font></div><div><font class="Apple-style-span" color="#000000">> y</font></div><div><font class="Apple-style-span" color="#000000">#0=(vertex</font></div><div><font class="Apple-style-span" color="#000000">    1</font></div><div><font class="Apple-style-span" color="#000000">    (list #1=(vertex 0 '() (list #0# #2=(vertex 2 '(#1# #2#) '(#2#)))))</font></div><div><font class="Apple-style-span" color="#000000">    '())</font></div><div><font class="Apple-style-span" color="#000000">> (set-vertex-s! x (vertex-s y))</font></div><div><font class="Apple-style-span" color="#000000">> x</font></div><div><font class="Apple-style-span" color="#000000">#0=(vertex</font></div><div><font class="Apple-style-span" color="#000000">    0</font></div><div><font class="Apple-style-span" color="#000000">    #1='(#0#)</font></div><div><font class="Apple-style-span" color="#000000">    (list (vertex 1 #1# '()) #2=(vertex 2 '(#0# #2#) '(#2#))))</font></div></blockquote><br></div><div><br></div><div>Does OCAML allow rational sets? -- Matthias</div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div><br><div><div>On Jul 26, 2013, at 5:25 PM, Nicholas Labich wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><div dir="ltr">I'm running into what I find to be surprising behavior with circular structures (vertices of a simple graph).<div><br></div><div>Graphically (see code below to reproduce):</div><div>0 --> 1 ;; no problem</div> <div>2-+      ;; also no problem<br><div> ^-+</div><div><br></div><div>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.</div> </div><div><br></div><div>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.</div> <div><br></div><div>Any insight would be much appreciated.</div><div><br></div><div>Nick</div><div><br></div><div><div>Welcome to Racket v5.90.0.2.</div><div>> (struct vertex (value preds succs) #:mutable #:transparent)</div> <div>> (define v0 (vertex 0 (set) (set)))</div><div>> (define v1 (vertex 1 (set) (set)))</div><div>> (set-vertex-succs! v0 (set v1))</div><div>> (set-vertex-preds! v1 (set v0)) ;; 0 --> 1</div><div>> (equal? v0 (set-first (vertex-preds v1)))</div> <div>#t</div><div>> (define v2 (vertex 2 (set) (set)))</div><div>> (set-vertex-preds! v2 (set v2)) ;; 2--+</div><div>> (set-vertex-succs! v2 (set v2)) ;; ^--+</div><div>> v2</div><div>#0=(vertex 2 (set #0#) (set #0#))</div> <div>;; try to add the already existing set</div> <div>> (set-vertex-succs! v0 (set-add (vertex-succs v0) v2)) ;; loops and loops</div><div>  C-c C-c^Cuser break</div><div>  context...:</div><div> .../racket/collects/racket/private/set-types.rkt:447:3: hash-proc</div> <div> .../racket/collects/racket/private/set-types.rkt:447:3: hash-proc</div><div> .../racket/collects/racket/private/set-types.rkt:447:3: hash-proc</div><div> .../racket/collects/racket/private/set-types.rkt:447:3: hash-proc...</div> <div>;; try to make a new set instead</div><div>> (set-vertex-succs! v0 (set v1 v2))</div><div>  C-c C-c^Cuser break</div><div>  context...:</div><div>  .../racket/collects/racket/private/set-types.rkt:447:3: hash-proc</div> <div>  .../racket/collects/racket/private/set-types.rkt:447:3: hash-proc</div> <div>  .../racket/collects/racket/private/set-types.rkt:447:3: hash-proc</div><div>  .../racket/collects/racket/private/set-types.rkt:447:3: hash-proc...</div><div>  </div><div>> (shared ([v0 (vertex 0 (set) succs0)]</div> <div>           [v1 (vertex 1 preds1 (set))]</div><div>           [v2 (vertex 2 preds2 succs2)]</div>           [succs0 (set v1 v2)]<div>           [preds1 (set v0)]</div><div>           [preds2 (set v0 v2)]</div><div>           [succs2 (set v2)])</div> <div>    (values v0 v1 v2))</div><div>(vertex 0 (set) (set #0=(vertex 2 (set #0#) (set #0#))))</div><div>(vertex 1 (set (vertex 0 (set) (set #0=(vertex 2 (set #0#) (set #0#))))) (set))</div><div>#0=(vertex 2 (set #0#) (set #0#))</div> <div>;; I must be using `shared' incorrectly...</div></div></div> ____________________<br>  Racket Users list:<br>  <a href="http://lists.racket-lang.org/users">http://lists.racket-lang.org/users</a><br></blockquote></div><br></body></html>