Michael Bayer wrote: > On Nov 8, 2007, at 11:32 AM, svilen wrote: > > >> mmmh. u can think of splitting the Visitor into 3: Guide (who >> traverses _everything_ given), Visitor (who does things), and >> intermediate Decisor, who decides where to go / what to do. But this >> can get complicated (slow) although it would be quite clear who does >> what. >> Also, do have both onEntry and onExit for each node; i am sure some >> operations will require both; first to gather info, second to make a >> decision about what to do with it while still at that level. >> >> i've done quite a lot of tree/expression traversers, and while >> readonly walking doesnot care much if on entry or on exit (except if >> u want depth or breadth first), replacements-in-place and >> copy+replace sometimes needed both entry and exit hooks, + they where >> conditional like in leafs. >> > > i think you should come up with your own ACP and lets take a look at > it. while i can get various ACP ideas to work further and further, > im still able to come up with plenty of cases where none of them work > and its because the structure of a clauseelement really isnt a tree. > the same node can be represented many times largely because columns > reference their parent table. > u mean a graph? mmm no. IMO an expression is a tree of nodes, each node points to some element of another space (metadata things+bindparams+...), and many nodes can point to same element, and eventualy many elements can hold same value (but be different elements - e.g. literal(1) and another literal(1) - not sure about whether this is usable). So traversing the (original) tree is one thing; what to do with the elements pointed by the nodes is another decision; e.g.. whether to process multiple-referred elements multiple times or just one, etc.
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