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TODO.md

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clingo 5

  • address _ in negated literals
    • use _ or maybe *
  • add sort-constraint
    • order(B,A) :- (A, B) = #sort{ X : p(X) }.
    • order(A,B) :- ((_,A), (_,B)) = #sort{ K,X : p(X), key(X,K) }.
  • profiling
  • sorting via conditional literals became less efficient with the latest implementation in some cases
  • projection is disabled in non-monotone constructs for now it could be enabled again if equivalences are used for affected atoms
  • remove CSP support
  • shifting of disjunctions

constraints

  • integrate constraint variables tighter into the gringo language
    • any term can contain csp variables
    • use HT_LC as basis
  • csp terms could be supported in aggregates too
  • when the value of a csp term is required rewriting has to happen
    • p(f($X+3)) becomes p(f(Aux)), Aux = $X+3
  • supporting csp terms in functions symbols in build-ins is more tricky
    • f($X+3) < g($Y+1)
    • a translation as above is unsafe
    • the literal is a tautology

memory management

  • I think that the proper way to handle symbols is to use reference counting
    • the c api would have to put the burden of reference counting on the user
    • the APIs can provide reference counted symbols
  • symbols should only be owned in key locations where the reference count is increased
    • for example a domain owns a symbol and can also take care of flyweighting it
  • touching the counters should be avoided as much as possible during grounding
    • during the backtraking based instantiation a very limited set of intermediate symbols is created
    • these intermediate symbols can be freed upon backtracking (if they have not been added to a domain)
    • the temporary symbols may refer to owned symbols without increasing their reference count
    • this has the advantage that insertion into hash tables and touching of reference counts only happens when a symbol is commited into a domain
  • implementing this should not be terribly difficult but affects a lot of code

misc

  • enlarge test suites
  • incremental programs
    • atm indexes have to be cleared and recreated afterwards
      • it might be a good idea to optimize this and reuse indices later on
      • for now just clear them to not have them dangling around
  • missing features in view of the ASP standard
    • queries
  • assignment rewriting
    • enqueue: expr(X,Z,Val):-expr(X,Y,Val_1)?,sing_term(Y,Z,Val_2)?,Val=(Val_1+Val_2),#X0=(Val_1+Val_2),#X0=Val.
    • handle assignments in a more clever way...
  • it would be nice to block grounding of rules if one index is empty (maybe even delaying the filling of indices if one index is empty)
  • indices could be specialized to handle zero-ary predicates more efficiently
    • there could be one domain for all zero-ary predicates
  • detect ground rules and implement more clever groundig
  • domains
    • using a value as representation is wasteful
    • uses one unordered_map to much
  • predicate indices
    • using a valvec as key is wasteful
    • uses one unordered_map too much
  • on large instances both optimizations should safe a lot of memory