//tabstop=4
//*****************************************************************************/
// Project: jpl
//
// File: $Id: Query.java,v 1.2 2007-09-27 15:25:32 vsc Exp $
// Date: $Date: 2007-09-27 15:25:32 $
// Author: Fred Dushin <fadushin@syr.edu>
//
//
// Description:
//
//
// -------------------------------------------------------------------------
// Copyright (c) 2004 Paul Singleton
// Copyright (c) 1998 Fred Dushin
// All rights reserved.
//
// This library is free software; you can redistribute it and/or
// modify it under the terms of the GNU Library Public License
// as published by the Free Software Foundation; either version 2
// of the License, or (at your option) any later version.
//
// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Library Public License for more details.
//*****************************************************************************/
package jpl;
import java.util.Enumeration;
import java.util.Hashtable;
import java.util.Map;
import java.util.Vector;
import jpl.fli.*;
//----------------------------------------------------------------------/
// Query
/**
* A Query instance is created by an application in order to query the Prolog database
* (or to invoke a built-in predicate).
* It is initialised with a
* Compound (or Atom) denoting the goal which is to be called, and also contains assorted private state
* relating to solutions. In some future version, it may contain details of the module
* in which the goal is to be called.<p>
* A Query is either open or closed: when closed, it has no connection to the Prolog system;
* when open, it is linked to an active goal within a Prolog engine.<p>
* The Query class implements the Enumeration interface,
* through which one can obtain successive solutions. The Enumeration
* hasMoreElements() method returns true if the call or redo succeeded (otherwise
* false), and if the call or redo did succeed, the nextElement() method returns
* a Hashtable representing variable bindings; the elements in the
* Hashtable are Terms, indexed by the (String) names of the Variables with which they are associated.
* For example, if <i>p(a)</i> and <i>p(b)</i> are facts in the Prolog
* database, then the following is equivalent to printing all
* the solutions to the Prolog query <i>p(X)</i>:
* <pre>
* Variable X = new Variable("X");
* Term arg[] = { X };
* Query q = new Query("p", arg);
*
* while (q.hasMoreElements()){
* Term bound_to_x = ((Hashtable) q.nextElement()).get("X");
* System.out.println(bound_to_x);
* }
* </pre>
* Make sure to close the Query (using the close() method) if you do not need
* any further solutions which it may have.
* It is safe (although redundant) to close a Query whose solutions are already exhausted,
* or which is already closed.
*
* To obtain just one solution from a Query, use the oneSolution() method.
*
* To obtain all solutions, use the allSolutions() method.
*
* To obtain at most N solutions, use the nSolutions() method.
*
* To determine merely whether the Query is provable,
* use the hasSolution() method
* (i.e. has at least one solution).
* <hr>
* <i>
* Copyright (C) 2007 Paul Singleton<p>
* Copyright (C) 1998 Fred Dushin
* <p>
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Library Public License
* as published by the Free Software Foundation; either version 2
* of the License, or (at your option) any later version.
* <p>
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Library Public License for more details.<p>
* </i>
* <hr>
* @author Fred Dushin <fadushin@syr.edu>
* @version $Revision: 1.2 $
*/
// Implementation notes:
//
//----------------------------------------------------------------------/
public class Query implements Enumeration {
//==================================================================/
// Attributes
//==================================================================/
private static Map m = new Hashtable(); // maps (engine_t) engine handle to (Query) topmost query
/**
* the Compound (hence perhaps an Atom, but not Integer, Float or Variable) corresponding to the goal of this Query
*/
protected final Compound goal_; // set by all initialisers
protected final String hostModule = "user"; // until revised constructors allow this to be specified
protected final String contextModule = "user"; // until revised constructors allow this to be specified
/**
* @deprecated Use .goal().name() instead.
* @return the name of this Query's goal (redundant, deprecated)
*/
public final String name() {
return goal_.name(); // it can only be a Compound or Atom
}
/**
* @deprecated Use .goal().args() instead.
* @return the arguments of this Query's goal (redundant, deprecated)
*/
public final Term[] args() {
return goal_.args();
}
/**
* Returns the Compound (hence perhaps an Atom) which is the goal of this Query
* @return a Term representing the goal of this Query
*/
public final Compound goal() {
return goal_;
}
//==================================================================/
// Constructors and Initialization
//==================================================================/
//------------------------------------------------------------------/
// Query
/**
* This constructor creates a Query whose goal is the specified Term.
* The Query is initially closed.
* <b>NB</b> Creating an instance of the Query class does not
* result in a call to a Prolog engine.
* <b>NB</b> The goal can be a Compound or an Atom (Atom extends Compound), but cannot be an instance
* of jpl.Float, jpl.Integer or jpl.Variable.
* @param t the goal of this Query
*/
public Query(Term t) { // formerly insisted (confusingly) on a Compound (or Atom)
this.goal_ = Query1(t);
}
private Compound Query1(Term t) {
if (t instanceof Compound) {
return (Compound) t;
} else if (t instanceof Integer) {
throw new JPLException("a Query's goal must be an Atom or Compound (not an Integer)");
} else if (t instanceof Float) {
throw new JPLException("a Query's goal must be an Atom or Compound (not a Float)");
} else if (t instanceof Variable) {
throw new JPLException("a Query's goal must be an Atom or Compound (not a Variable)");
} else {
throw new JPLException("a Query's goal must be an Atom or Compound");
}
}
// Query
/**
* If text denotes an atom, this constructor is shorthand for
* <font face="monospace">new Query(new Compound(name,args))</font>,
* but if text denotes a term containing N query (?) symbols
* and there are N args, each query is replaced by its corresponding arg
* to provide the new Query's goal.
*
* @param text the name of the principal functor of this Query's goal
* @param args the arguments of this Query's goal
*/
public Query(String text, Term[] args) {
this(Query1(text, args));
}
// convenience case for a single arg
public Query(String text, Term arg) {
this(Query1(text, new Term[] { arg }));
}
private static Term Query1(String text, Term[] args) {
Term t = Util.textToTerm(text);
if (t instanceof Atom) {
return new Compound(text, args);
} else {
return t.putParams(args);
}
}
// Query
/**
* This constructor builds a Query from the given Prolog source text.
* Throws PrologException containing error(syntax_error(_),_) if text is invalid.
*
* @param text the Prolog source text of this Query
*/
public Query(String text) {
this(Util.textToTerm(text));
}
//==================================================================/
// Making Prolog Queries
//==================================================================/
/**
* These variables are used and set across the hasMoreElements
* and nextElement Enumeration interface implementation
*/
private boolean open = false;
// the following state variables are used and defined only if this query is open:
// private boolean called = false; // open/get/close vs. hasMoreSolutions/nextSolution
private engine_t engine = null; // handle of attached Prolog engine iff open, else null
private Query subQuery = null; // the open Query (if any) on top of which this open Query is stacked, else null
private predicate_t predicate = null; // handle of this Query's predicate iff open, else undefined
// private fid_t fid = null; // id of current Prolog foreign frame iff open, else null
// private fid_t fid2 = null; // id of experimental inner frame
private term_t term0 = null; // term refs of this Query's args iff open, else undefined
private qid_t qid = null; // id of current Prolog query iff open, else null
//------------------------------------------------------------------/
// hasMoreSolutions
/**
* This method returns true if JPL was able to initiate a "call" of this
* Query within a Prolog engine. It is designed to be used
* with the nextSolution() method to retrieve one or
* more substitutions in the form of Hashtables. To iterate through
* all the solutions to a Query, for example, one might write
* <pre>
* Query q = // obtain Query reference
* while (q.hasMoreSolutions()) {
* Hashtable solution = q.nextSolution();
* // process solution...
* }
* </pre>
* To ensure thread-safety, you should wrap sequential calls to
* this method in a synchronized block, using the static
* lock method to obtain the monitor.
* <pre>
* Query q = // obtain Query reference
* synchronized ( jpl.Query.lock() ){
* while ( q.hasMoreElements() ){
* Hashtable solution = q.nextSolution();
* // process solution...
* }
* }
* </pre>
*
* @return true if the Prolog query succeeds; otherwise false.
*/
public synchronized final boolean hasMoreSolutions() {
if (!open) {
open();
}
return get1();
}
//------------------------------------------------------------------/
// open
/**
* This method returns true if JPL was able to initiate a "call" of this
* Query within the Prolog engine. It is designed to be used
* with the getSolution() and close() methods to retrieve one or
* more substitutions in the form of Hashtables.
* To ensure thread-safety, you should wrap sequential calls to
* this method in a synchronized block, using the static
* lock method to obtain the monitor.
* <pre>
* Query q = // obtain Query reference
* synchronized ( jpl.Query.lock() ){
* while ( q.hasMoreElements() ){
* Hashtable solution = q.nextSolution();
* // process solution...
* }
* }
* </pre>
* <p>
* If this method is called on an already-open Query,
* or if the query cannot be set up for whatever reason,
* then a JPLException will be thrown.
*/
public synchronized final void open() {
if (open) {
throw new JPLException("Query is already open");
}
// int self = Prolog.thread_self();
// System.out.println("JPL thread_self()=" + self);
if (Prolog.thread_self() == -1) { // this Java thread has no attached Prolog engine?
engine = Prolog.attach_pool_engine(); // may block for a while, or fail
// System.out.println("JPL attaching engine[" + engine.value + "] for " + this.hashCode() + ":" + this.toString());
} else { // this Java thread has an attached engine
engine = Prolog.current_engine();
// System.out.println("JPL reusing engine[" + engine.value + "] for " + this.hashCode() + ":" + this.toString());
}
if (m.containsKey(new Long(engine.value))) {
subQuery = (Query) m.get(new Long(engine.value)); // get this engine's previous topmost query
// System.out.println("JPL reusing engine[" + engine.value + "] pushing " + subQuery.hashCode() + ":" + subQuery.toString());
} else {
subQuery = null;
}
m.put(new Long(engine.value), this); // update this engine's topmost query
//
// here, we must check for a module prefis, e.g. jpl:jpl_modifier_bit(volatile,T)
String module;
Term goal;
if (goal_.hasFunctor(":", 2)) {
if (goal_.arg(1).isAtom()) {
module = goal_.arg(1).name();
} else if (goal_.arg(1).isVariable()) {
throw new PrologException(Util.textParamsToTerm("error(instantiation_error,?)", new Term[] { goal_ }));
} else {
throw new PrologException(Util.textParamsToTerm("error(type_error(atom,?),?)", new Term[] { goal_.arg(1), goal_ }));
}
goal = goal_.arg(2);
} else {
module = contextModule;
goal = goal_;
}
predicate = Prolog.predicate(goal.name(), goal.arity(), module); // was hostModule
// fid = Prolog.open_foreign_frame(); // always succeeds?
Map varnames_to_vars = new Hashtable();
term0 = Term.putTerms(varnames_to_vars, goal.args());
// THINKS: invert varnames_to_Vars and use it when getting substitutions?
qid = Prolog.open_query(Prolog.new_module(Prolog.new_atom(contextModule)), Prolog.Q_CATCH_EXCEPTION, predicate, term0);
open = true;
// called = false;
}
private final boolean get1() { // try to get the next solution; if none, close the query;
// if (fid2 != null) { // PS 23/Mar/2007 ensure inner frame is closed
// Prolog.close_foreign_frame(fid2);
// fid2 = null;
// }
if (Prolog.next_solution(qid)) {
// fid2 = Prolog.open_foreign_frame(); // PS 23/Mar/2007 open an inner frame
// called = true; // OK to call get2()
return true;
} else {
// if failure was due to throw/1, build exception term and throw it
term_t exception_term_t = Prolog.exception(qid);
if (exception_term_t.value != 0L) {
Term exception_term = Term.getTerm(new Hashtable(), exception_term_t);
close();
throw new PrologException(exception_term);
} else {
close();
return false;
}
}
}
//------------------------------------------------------------------/
// getSolution
/**
* This method returns a java.util.Hashtable, which represents
* a set of bindings from the names of query variables to terms within the solution.
* <p>
* For example, if a Query has an occurrence of a jpl.Variable,
* say, named "X", one can obtain the Term bound to "X" in the solution
* by looking up "X" in the Hashtable.
* <pre>
* Variable x = new Variable("X");
* Query q = // obtain Query reference (with x in the Term array)
* while (q.hasMoreSolutions()) {
* Hashtable solution = q.nextSolution();
* // make t the Term bound to "X" in the solution
* Term t = (Term) solution.get("X");
* // ...
* }
* </pre>
* Programmers should obey the following rules when using this method.
* <menu>
* <li> The nextSolution() method should only be called after the
* hasMoreSolutions() method returns true; otherwise a JPLException
* will be raised, indicating that the Query is no longer open.
* <li> The nextSolution() and hasMoreSolutions() should be called
* in the same thread of execution, for a given Query
* instance.
* </menu>
*
* This method will throw a JPLException if Query is not open.
*
* @return A Hashtable representing a substitution, or null
*/
public synchronized final Hashtable getSolution() {
// oughta check: Query is open and thread has its engine
if (get1()) {
return get2();
} else {
return null;
}
}
public synchronized final Hashtable getSubstWithNameVars() {
// oughta check: Query is open and thread has its engine
if (get1()) {
return get2WithNameVars();
} else {
return null;
}
}
//------------------------------------------------------------------/
// nextSolution
/**
* This method returns a java.util.Hashtable, which represents
* a binding from the names of query variables to terms within the solution.
* <p>
* For example, if a Query has an occurrence of a jpl.Variable,
* say, named "X", one can obtain the Term bound to "X" in the solution
* by looking up "X" in the Hashtable.
* <pre>
* Variable x = new Variable("X");
* Query q = // obtain Query reference (with x in the Term array)
* while (q.hasMoreSolutions()) {
* Hashtable solution = q.nextSolution();
* // make t the Term bound to "X" in the solution
* Term t = (Term) solution.get("X");
* // ...
* }
* </pre>
* Programmers should obey the following rules when using this method.
* <menu>
* <li> The nextSolution() method should only be called after the
* hasMoreSolutions() method returns true; otherwise a JPLException
* will be raised, indicating that the Query is no longer open.
* <li> The nextSolution() and hasMoreSolutions() should be called
* in the same thread of execution, for a given Query
* instance.
* </menu>
*
* This method will throw a JPLException if Query is not open.
*
* @return A Hashtable representing a substitution.
*/
public synchronized final Hashtable nextSolution() {
return get2();
}
private final Hashtable get2() {
if (!open) {
throw new JPLException("Query is not open");
} else {
Hashtable substitution = new Hashtable();
// NB I reckon computeSubstitutions needn't be in Term (but where else?)
Term.getSubsts(substitution, new Hashtable(), goal_.args);
return substitution;
}
}
// assumes that Query's last arg is a Variable which will be bound to a [Name=Var,..] dict
private final Hashtable get2WithNameVars() {
if (!open) {
throw new JPLException("Query is not open");
} else {
Term[] args = goal_.args; // for slight convenience below
Term argNV = args[args.length - 1]; // the Query's last arg
String nameNV = ((Variable) argNV).name; // its name
// get the [Name=Var,..] dict from the last arg
Map varnames_to_Terms1 = new Hashtable();
Map vars_to_Vars1 = new Hashtable();
args[args.length - 1].getSubst(varnames_to_Terms1, vars_to_Vars1);
Hashtable varnames_to_Terms2 = new Hashtable();
Term nvs = (Term) varnames_to_Terms1.get(nameNV);
Map vars_to_Vars2 = Util.namevarsToMap(nvs);
for (int i = 0; i < args.length - 1; ++i) {
args[i].getSubst(varnames_to_Terms2, vars_to_Vars2);
}
return varnames_to_Terms2;
}
}
//------------------------------------------------------------------/
// hasMoreElements
/**
* This method implements part of the java.util.Enumeration
* interface. It is a wrapper for hasMoreSolutions.
*
* @return true if the Prolog query yields a (or another) solution, else false.
*/
public synchronized final boolean hasMoreElements() {
return hasMoreSolutions();
}
//------------------------------------------------------------------/
// nextElement
/**
* This method implements part of the java.util.Enumeration
* interface. It is a wrapper for nextSolution.
* <p>
*
* @return A Hashtable representing a substitution.
*/
public synchronized final Object nextElement() {
return nextSolution();
}
public synchronized final void rewind() {
close();
}
/**
* This method can be used to close an open query before its solutions are exhausted.
* It is called automatically when solutions are exhausted, i.e. when hasMoreSolutions() fails.
* Calling close() on an already closed Query is harmless (has no effect).<p>
*
* Here is one way to get the first three solutions to a Query:
* <pre>
* Query q = new Query(predicate, args);
* Hashtable sub1 = (Hashtable) q.nextSolution();
* Hashtable sub2 = (Hashtable) q.nextSolution();
* Hashtable sub3 = (Hashtable) q.nextSolution();
* q.close();
* </pre><p>
*/
public synchronized final void close() {
if (!open) {
return; // it is not an error to attempt to close a closed Query
}
if (Prolog.thread_self() == -1) {
throw new JPLException("no engine is attached to this thread");
}
if (Prolog.current_engine().value != engine.value) {
throw new JPLException("this Query's engine is not that which is attached to this thread");
}
Query topmost = (Query) m.get(new Long(engine.value));
if (topmost != this) {
throw new JPLException("this Query (" + this.hashCode() + ":" + this.toString() + ") is not topmost (" + topmost.hashCode() + ":" + topmost.toString() + ") within its engine["
+ engine.value + "]");
}
Prolog.close_query(qid);
qid = null; // for tidiness
m.remove(new Long(engine.value));
if (subQuery == null) { // only Query open in this engine?
if (Prolog.current_engine_is_pool()) { // this (Query's) engine is from the pool?
Prolog.release_pool_engine();
// System.out.println("JPL releasing engine[" + engine.value + "]");
} else {
// System.out.println("JPL leaving engine[" + engine.value + "]");
}
} else {
m.put(new Long(engine.value), subQuery);
// System.out.println("JPL retaining engine[" + engine.value + "] popping subQuery(" + subQuery.hashCode() + ":" + subQuery.toString() + ")");
}
open = false; // this Query is now closed
engine = null; // this Query, being closed, is no longer associated with any Prolog engine
subQuery = null; // this Query, being closed, is not stacked upon any other Query
}
/**
* calls the Query's goal to exhaustion
* and returns an array of zero or more Hashtables of zero or more variablename-to-term bindings (each Hashtable represents a solution, in the order in which they were found).
* @return an array of zero or more Hashtables of zero or more variablename-to-term bindings (each Hashtable represents a solution, in the order in which they were found)
* <b>NB</b> in JPL 1.0.1, this method (inconsistently) returned null when a Query had no solutions;
* in JPL 2.x onwards it returns an empty array (thus the length of the array is, in every case,
* the quantity of solutions).<p>
* <b>NB</b> in JPL 1.0.1, bindings were keyed (awkwardly) by Variable instances;
* in JPL 2.x onwards they are keyed by the (String) names of variables,
* which is consistent with the Term type being just a concrete syntax for terms (and hence queries).<p>
*/
public synchronized final Hashtable[] allSolutions() {
if (open) {
throw new JPLException("Query is already open");
} else {
// get a vector of solutions:
Vector v = new Vector();
while (hasMoreSolutions()) {
v.addElement(nextSolution());
}
// turn the vector into an array:
Hashtable solutions[] = new Hashtable[v.size()]; // 0 solutions -> Hashtable[0]
v.copyInto(solutions);
return solutions;
}
}
/**
* This static method creates a Query whose goal is the given Term,
* calls it to exhaustion,
* and returns an array of zero or more Hashtables of zero or more variablename-to-term bindings (each Hashtable represents a solution, in the order in which they were found).
* Throws JPLException if goal is neither a jpl.Atom nor a jpl.Compound.
*
* @return an array of zero or more Hashtables of zero or more variablename-to-term bindings (each Hashtable represents a solution, in the order in which they were found)
*
* @param goal the goal of this Query
*/
public static final Hashtable[] allSolutions(Term goal) {
return (new Query(goal)).allSolutions();
}
/**
* This static method creates a Query from the given Prolog source text fragment,
* calls it to exhaustion,
* and returns an array of zero or more Hashtables of zero or more variablename-to-term bindings (each Hashtable represents a solution, in the order in which they were found).
* Throws PrologException containing error(syntax_error(_),_) if text is invalid.
*
* @return an array of zero or more Hashtables of zero or more variablename-to-term bindings (each Hashtable represents a solution, in the order in which they were found)
*
* @param text a Prolog source text fragment denoting a goal
*/
public static final Hashtable[] allSolutions(String text) {
return (new Query(text)).allSolutions();
}
/**
* If text denotes (in traditional Prolog source syntax) a term containing N questionmark (?) symbols and there are N accompanying Term params,
* this static method replaces each questionmark symbol by its respective param,
* calls the resulting goal to exhaustion,
* and returns an array of zero or more Hashtables of zero or more variablename-to-term bindings (each Hashtable represents a solution, in the order in which they were found).
*
* Otherwise, if text denotes an atom, this static method creates a Query
* where text is the name of the goal and params are the args;
* the resulting goal is then called as above.
* This letter mode is redundant, deprecated (informally), and retained only for backward compatibility.
*
* @return an array of zero or more Hashtables of zero or more variablename-to-term bindings (each Hashtable represents a solution, in the order in which they were found)
*
* @param text the Prolog source text of a goal, in which questionmarks are regarded as substitutible parameters
* @param params terms to be substituted for the respective questionmarks in the query text
*/
public static final Hashtable[] allSolutions(String text, Term[] params) {
return (new Query(text, params)).allSolutions();
}
/**
* calls the Query's goal to exhaustion or until N solutions are found, whichever is sooner,
* and returns an array containing (as possibly empty Hashtables of variablename-to-term bindings) every found solution (in the order in which they were found).
* @return an array of Hashtables (possibly none), each of which is a solution
* (in the order in which they were found) of the Query; at most 'n' solutions will be found and returned.
* <b>NB</b> in JPL 1.0.1, this method (inconsistently) returned null when a Query had no solutions;
* in JPL 2.x onwards it returns an empty array (thus the length of the array is, in every case,
* the quantity of solutions).<p>
* <b>NB</b> in JPL 1.0.1, bindings were keyed (awkwardly) by Variable instances;
* in JPL 2.x onwards they are keyed by the (String) names of variables,
* which is consistent with the Term type being just a concrete syntax for terms (and hence queries).<p>
*/
public synchronized final Hashtable[] nSolutions(long n) {
if (open) {
throw new JPLException("Query is already open");
} else {
// get a vector of solutions:
Vector v = new Vector();
for (long i = 0; i++ < n && hasMoreSolutions();) {
v.addElement(nextSolution());
}
// turn the vector into an array:
Hashtable solutions[] = new Hashtable[v.size()]; // 0 solutions -> Hashtable[0]
v.copyInto(solutions);
return solutions;
}
}
/**
* This static method creates a Query whose goal is the given Term,
* calls it to exhaustion or until N solutions are found, whichever is sooner,
* and returns an array containing (as possibly empty Hashtables of variablename-to-term bindings) every found solution (in the order in which they were found).
* Throws JPLException if goal is neither a jpl.Atom nor a jpl.Compound.
*
* @param goal the goal of this Query
*/
public static final Hashtable[] nSolutions(Term goal, long n) {
return (new Query(goal)).nSolutions(n);
}
/**
* This static method creates a Query from the given Prolog source text fragment,
* calls it to exhaustion or until N solutions are found, whichever is sooner,
* and returns an array containing (as possibly empty Hashtables of variablename-to-term bindings) every found solution (in the order in which they were found).
* Throws PrologException containing error(syntax_error(_),_) if text is invalid.
*
* @param text a Prolog source text fragment denoting a goal
*/
public static final Hashtable[] nSolutions(String text, long n) {
return (new Query(text)).nSolutions(n);
}
/**
* If text denotes (in traditional Prolog source syntax) a term containing N questionmark (?) symbols and there are N accompanying params,
* this static method replaces each questionmark symbol by its respective param,
* calls the resulting goal to exhaustion or until N solutions are found, whichever is sooner,
* and returns an array containing (as possibly empty Hashtables of variablename-to-term bindings) every found solution (in the order in which they were found).
*
* Otherwise, if text denotes an atom, this static method creates a Query
* where text is the name of the goal and params are the args;
* the resulting goal is then called as above.
* This latter mode is redundant, deprecated (informally), and retained only for backward compatibility.
*
* @param text the Prolog source text of a goal, in which questionmarks are regarded as substitutible parameters
* @param params terms to be substituted for the respective questionmarks in the query text
*/
public static final Hashtable[] nSolutions(String text, Term[] params, long n) {
return (new Query(text, params)).nSolutions(n);
}
/**
* Returns the first solution, if any, as a (possibly empty) Hashtable of variablename-to-term bindings, else null.
*
* This method will throw a JPLException if this Query is already open (and the Query will remain open as before).
* Otherwise, upon return, the Query will be closed.
* @return the first solution, if the query has one, as a (possibly empty) Hashtable.
* If the return value is null, this means that the Query has no solutions.<p>
*/
public synchronized final Hashtable oneSolution() {
if (open) {
throw new JPLException("Query is already open");
} else {
Hashtable solution;
if (hasMoreSolutions()) {
solution = nextSolution();
close(); // safe, whether or not this is the only solution
} else {
solution = null;
}
return solution;
}
}
/**
* This static method creates a Query (whose goal is the specified Term)
* and calls it at most once, returning the first solution, if there is one, as a (possibly empty) Hashtable, else null.
* The goal can be a jpl.Atom or a jpl.Compound, but cannot be an instance
* of jpl.Float, jpl.Integer or jpl.Variable.
*
* @param goal the goal of this Query
*/
public static final Hashtable oneSolution(Term goal) {
return (new Query(goal)).oneSolution();
}
/**
* This static method creates a Query from the given Prolog source text fragment,
* and calls it at most once, returning the first solution, if there is one, as a (possibly empty) Hashtable, else null.
* Throws PrologException containing error(syntax_error(_),_) if text is invalid.
*
* @param text a Prolog source text fragment denoting a goal
*/
public static final Hashtable oneSolution(String text) {
return (new Query(text)).oneSolution();
}
/**
* If text denotes (in traditional Prolog source syntax) a term containing N questionmark (?) symbols
* and there are N params, each questionmark symbol is replaced by its respective param
* to provide the goal of this query:
* the resulting goal is then called (at most once) and the first solution, if there is one, is returned as a (possibly empty) Hashtable, else null.
*
* Otherwise, if text denotes an atom, this static method creates a Query
* where text is the name of the goal and params are the args;
* the resulting goal is then called as above.
* This latter mode is redundant, deprecated (informally), and retained only for backward compatibility.
*
* @param text the Prolog source text of a goal, in which questionmarks are regarded as substitutible parameters
* @param params terms to be substituted for the respective questionmarks in the query text
*/
public static final Hashtable oneSolution(String text, Term[] params) {
return (new Query(text, params)).oneSolution();
}
/**
* This method will attempt to call this Query's goal within an available Prolog engine.
* @return the provability of the Query, i.e. 'true' if it has at least
* one solution, 'false' if the call fails without finding a solution.<p>
*
* Only the first solution (if there is one) will be found;
* any bindings will be discarded, and the Query will be closed.<p>
* This method will throw a JPLException if this Query is already open.
*
* @deprecated Use .hasSolution() instead.
*/
public synchronized final boolean query() {
return oneSolution() != null;
}
/**
* This method will attempt to call this Query's goal within an available Prolog engine.
* @return the provability of the Query, i.e. 'true' if it has at least
* one solution, 'false' if the call fails without finding a solution.<p>
*
* Only the first solution (if there is one) will be found;
* any bindings will be discarded, and the Query will be closed.<p>
* This method will throw a JPLException if this Query is already open.
*/
public synchronized final boolean hasSolution() {
return oneSolution() != null;
}
/**
* This static method creates a Query (whose goal is the specified Term)
* and calls it at most once, returning true if a solution was found, else false.
* The goal can be a jpl.Atom or a jpl.Compound, but cannot be an instance
* of jpl.Float, jpl.Integer or jpl.Variable.
*
* @param goal the goal of this Query
*/
public static final boolean hasSolution(Term goal) {
return (new Query(goal)).hasSolution();
}
/**
* This static method creates a Query from the given Prolog source text
* and calls it at most once, returning true if a solution was found, else false.
* Throws PrologException containing error(syntax_error(_),_) if text is invalid.
*
* @param text the goal of this Query, as Prolog source text
*/
public static final boolean hasSolution(String text) {
return (new Query(text)).hasSolution();
}
/**
* If text denotes (in traditional Prolog source syntax) a term containing N questionmark (?) symbols
* and there are N params, each questionmark symbol is replaced by its corresponding arg
* to provide the new Query's goal: the resulting Query is called as described above.
*
* Otherwise, if text denotes an atom, this static method creates a Query
* where text is the name of its goal and args are its args;
* it then calls this goal (at most once) and returns true if a solution was found, else false.
* This latter mode is redundant, deprecated (informally), and retained only for backward compatibility.
*
* @param text the Prolog source text of a goal, in which questionmarks are regarded as substitutible parameters
* @param params terms to be substituted for the respective questionmarks in the query text
*/
public static final boolean hasSolution(String text, Term[] params) {
return (new Query(text, params)).hasSolution();
}
//
// this method doesn't work, but is intended to be called from another thread,
// to abort a Query which is open and possibly currently executing nextSolution() or similar
public final int abort() {
if (open) {
(new Thread(new Runnable() {
public void run() {
try {
int rc1 = Prolog.attach_engine(engine);
System.out.println("q.abort(): attach_engine() returns " + rc1);
int rc2 = Prolog.action_abort();
System.out.println("q.abort(): action_abort() returns " + rc2);
// int rc3 = Prolog.release_pool_engine();
// System.out.println("q.abort(): release_pool_engine() returns " + rc3);
} catch (Exception e) {
}
}
})).start(); // call the query in a separate thread
/*
int rc0a = Prolog.pool_engine_id(this.engine);
System.out.println("q.abort(): this.engine has id=" + rc0a);
engine_t e = Prolog.current_engine();
System.out.println("q.abort(): " + (e == null ? "no current engine" : "current engine id=" + Prolog.pool_engine_id(e)));
int rc0b = Prolog.release_pool_engine();
System.err.println("q.abort(): release_pool_engine() returns " + rc0b);
engine_t e2 = Prolog.current_engine();
System.out.println("q.abort(): " + (e == null ? "no current engine" : "current engine id=" + Prolog.pool_engine_id(e2)));
int rc1 = Prolog.attach_engine(this.engine);
System.out.println("q.abort(): attach_engine() returns " + rc1);
engine_t e3 = Prolog.current_engine();
System.out.println("q.abort(): " + (e == null ? "no current engine" : "current engine id=" + Prolog.pool_engine_id(e3)));
int rc2 = Prolog.action_abort();
System.out.println("q.abort(): action_abort() returns " + rc2);
int rc3 = Prolog.release_pool_engine();
System.out.println("q.abort(): release_pool_engine() returns " + rc3);
int rc4 = Prolog.attach_engine(e);
System.out.println("q.abort(): attach_engine() returns " + rc4);
*/
return 0;
} else {
System.out.println("q.abort(): query is not open");
return -1;
}
}
//==================================================================/
// misc
//==================================================================/
/**
* Returns a crude String representation of a Query.
*
* @return a crude String representation of a Query
*/
public String toString() {
return goal_.name + "( " + Term.toString(goal_.args) + " )";
}
//==================================================================/
// Methods (deprecated)
//==================================================================/
/**
* Returns a debug-friendly representation of a Query
*
* @return a debug-friendly representation of a Query
* @deprecated
*/
public String debugString() {
return "(Query " + goal_.name + " " + Term.debugString(goal_.args) + ")";
}
}