solve/it.unibo.tuprolog.solve/Solution

Solution

sealed interface Solution : Taggable<Solution> , Castable<Solution>

A type representing a solution to a goal, as produced by it.unibo.tuprolog.solve.Solver.solve.

Every Solution is one of three sealed subtypes, distinguished by isYes/isNo/isHalt (and matched exhaustively via whenIs):

Yes -- the goal succeeded, with solvedQuery and a Substitution.Unifier as substitution;
No -- the goal failed, substitution is Substitution.Fail and solvedQuery is null;
Halt -- resolution was aborted by a ResolutionException, carried in exception.

Construct instances via the companion's yes, no, halt factories.

Inheritors

Types

object Companion

sealed interface Halt : Solution

A type representing a failed (halted) solution because of an exception

sealed interface No : Solution

A type representing a failed solution

sealed interface Yes : Solution

A type representing the successful solution

Properties

abstract val exception: ResolutionException?

The exception that made resolution halt, if this is a Halt solution, or null otherwise

abstract val isHalt: Boolean

Whether this is a Halt (aborted by an exception) solution

abstract val isNo: Boolean

Whether this is a No (failed) solution

abstract val isYes: Boolean

Whether this is a Yes (successful) solution

abstract val query: Struct

The original goal to which this solution refers

abstract val solvedQuery: Struct?

The Struct representing the solution, or null in case of a non-successful solution

abstract val substitution: Substitution

The substitution that has been applied to find the solution, or a failed substitution

abstract val tags: Map<String, Any>

Functions

open fun <U : Solution> as(): U?

open fun asHalt(): Solution.Halt?

Casts the current Solution to Halt, if possible, or returns null otherwise

open fun asNo(): Solution.No?

Casts the current Solution to No, if possible, or returns null otherwise

open fun asYes(): Solution.Yes?

Casts the current Solution to Yes, if possible, or returns null otherwise

open fun <U : Solution> castTo(): U

open fun castToHalt(): Solution.Halt

Casts the current Solution to Halt, if possible

open fun castToNo(): Solution.No

Casts the current Solution to No, if possible

open fun castToYes(): Solution.Yes

Casts the current Solution to Yes, if possible

abstract fun cleanUp(): Solution

Returns a Solution equivalent to this one, but with every variable not occurring in query (nor bound, in substitution, to a variable occurring in query) removed from substitution. Useful to drop resolution-internal variables before presenting a solution to a user.

open fun containsTag(name: String): Boolean

open fun <T : Any> getTag(name: String): T?

abstract fun replaceTags(tags: Map<String, Any>): Solution

abstract fun valueOf(variable: Var): Term?

Returns the Term bound to variable in substitution, or null if variable is unbound (or this is not a Yes solution).

abstract fun valueOf(variable: String): Term?

Same as valueOf, but looking variable up by name rather than by Var instance.

open fun <T> whenIs(yes: (Solution.Yes) -> T? = null, no: (Solution.No) -> T? = null, halt: (Solution.Halt) -> T? = null, otherwise: (Solution) -> T = { throw IllegalStateException("Cannot handle solution $it") }): T

Exhaustively (or partially) pattern-matches this Solution against its three possible subtypes, invoking whichever of yes/no/halt corresponds to this solution's actual kind, or otherwise if that branch was left null (by default, throwing IllegalStateException).