Subject: Re: tranformations and node visiting
From: Jonathan Aldrich (jonal@cs.washington.edu)
Date: Fri Mar 02 2001 - 15:20:07 PST
> We could have a graph_visit_allowing_updates method (basically, compute the
> successors of a node and cache them before calling the user's closure), but I'm
> not sure if this handles all the cases we're talking about (I think it doesn't,
> actually). Alternatively, we could have that _allowing_updates method cache all
> the nodes in the graph into a vector, and then iterate out of that. This is
> essentially what you're doing in the solution, except in the client code rather
> than in the data structure itself. The drawback of my proposal is that a bunch
> of _allowing_updates wrapper methods have to be added to all the various
> traversal/do/visit methods over graphs.
I think this is a classic example of why we need first-class multimethods.
Imagine a method caching_visit, that takes a visit method and a thing to
do during the visit. It first builds a cached vector in the correct visit
order by invoking the visit method on an internal closure, then iterates
over the vector, calling the user's closure.
We could do this in Cecil with closures, but the interfaces and usage
scenario would be really ugly. Can't wait for Diesel!
Jonathan :-)
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