StreamsSolverFactory

The SolverFactory for :solve-streams, an experimental, Sequence-based resolution engine.

This is the factory that ultimately backs the deprecated Solver.streams accessor declared in :solve: that accessor locates this object at runtime -- by fully-qualified class name on the JVM, by module lookup on JS -- rather than depending on :solve-streams directly, which is why this object must remain a top-level, no-argument-constructible object named exactly StreamsSolverFactory in this package.

Every Solver produced here resolves goals by unfolding a tree of immutable states, lazily, as a Kotlin Sequence: each state's behave() yields its successor state(s) -- several of them at a choice point -- and an internal StateMachineExecutor flattens that tree depth-first into the Sequence<Solution> returned by Solver.solve. This differs from :solve-classic's explicit, iterator-driven finite-state machine (see the "state-machine" explanation page in the project documentation): there, backtracking is implemented via a mutable choice-point stack that the solver replays on demand; here, each state carries its own immutable copy of the execution context and backtracking simply falls out of how the lazy sequence is walked.

This engine is not production-ready. mutableSolverOf is unimplemented here -- it always throws NotImplementedError -- and a large share of the standard predicates exercised by 2P-Kt's shared conformance test suite are skipped for this engine in this module's tests (e.g. most of assert/retract, findall, arithmetic and type-checking predicates), meaning their behaviour under this resolution strategy is currently untested and not guaranteed to be ISO-conformant. This is why Solver.streams is marked @Deprecated as "experimental and not mature enough for general purpose usage". Prefer Solver.prolog (it.unibo.tuprolog.solve.classic.ClassicSolverFactory) for anything beyond experimenting with this alternative, more side-effect-free resolution style.

See also