Re: [Haskell-cafe] Wrong Answer Computing Graph Dominators

Your reasoning differs from the usual understanding of a null product (1 or True), as compared to a null sum (0 or False):

the list of nodes for which *any path* from source to x must touch, i.e., the list of dominators of x.

Here, "any path" means all paths, a logical conjunction: and [True, True] = True and [True ] = True and [ ] = True The empty case of all sources touching is True, so 12 is a valid dominator for 20 if there is no path from 12 to 20. Dan Denis Bueno wrote:

On Thu, Apr 17, 2008 at 11:32 AM, Denis Bueno wrote:

...

On Wed, Apr 16, 2008 at 2:33 PM, Bertram Felgenhauer wrote:

...

No. Data.Graph.Inductive.Query.Dominators is just buggy.

I have one more problem. For the attached graph, the dominators of the -20 node are computed correctly (namely, [-20,-1,11,12]). But the list of dominators for 20 is present, when in fact 20 isn't reachable from 12. I think 20 should be absent from the return value of `dom graph 12'. (And hence a call to `lookup 20 (dom graph 12)' should return Nothing.) Instead it returns [-20,-1,-3,11,12,-14,17].

Is my reasoning correct? I'd try to fix the code, but, I don't understand how it works.

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