[LOGIC-112] Incorrect results with tabled resolution Created: 05/Feb/13 Updated: 28/Jul/13 Resolved: 13/Mar/13
|Reporter:||Reinout Stevens||Assignee:||David Nolen|
We (authors of damp.qwal and damp.ekeko) are trying to track the cause of some indeterminism with respect to the solutions to a path query over a control flow graph. To this end, we wrote a small test case that mimics the qwal part of the query. This test case works under core.logic 0.7.5, but exhibits incorrect behavior in the latest release.
The test case illustrates two problems:
Both queries skip an arbitrary number of nodes (using patho), capture a node to obtain a solution (through unification), and skip an arbitrary number of nodes.
Second, we encountered a minor issue concerning the number of results returned by the faulty query. This sometimes changes when the file is recompiled.
More comments can be found in the code for the test case that is attached.
|Comment by David Nolen [ 13/Feb/13 3:10 PM ]|
Ok, I've confirmed the issue. Will look into it.
|Comment by David Nolen [ 11/Mar/13 8:37 AM ]|
I believe I have found the issue as well as the source of the nondeterminism. When we switched to sets away from lists for the cache I didn't fully think through the implications. The nondeterminism arises from the use of sets. We actually want a hybrid cache datatype that works like a list but can efficiently check for the existence of a cached answer w/o scanning the list.
|Comment by David Nolen [ 13/Mar/13 8:51 AM ]|