class Prolog (old, current in #1002855) [1002826]

!752

static class Prolog {
  boolean upperCaseVariables = false; // true for SNL, false for NL
  long varCount;
  boolean showStuff;
  new L<Entry> stack;
  Trail sofar = null;
  new L<Clause> program;
  long steps;
  new L<Native> natives;
  
  // stats
  int maxLevelSeen; // maximum stack level reached during computation
  long topUnifications;

  static interface Native {
    public boolean yo(Prolog p, Lisp term);
  }
  
  static class Var extends Lisp {
    long id;
    Lisp instance;
    
    *(S name) {
      super(name);
      instance = this;
    }
    
    *(long id) {
      super("___");
      this.id = id;
      instance = this;
    }
    
    void reset() { instance = this; }
    
    public String toString() {
      if (instance != this)
        ret instance.toString();
      ret isUserVar() ? getName() : "_" + id;
    }
    
    boolean isUserVar() {
      ret id == 0;
    }
    
    S getName() {
      ret head;
    }
    
    Lisp getValue() {
      Lisp l = instance;
      while (l instanceof Var) {
        Var v = cast l;
        if (v.instance == v)
          ret v;
        l = v.instance;
      }
      ret l;
    }
  }
  
  class Clause {
    Lisp head;
    Goal body;
    
    *(Lisp *head, Goal *body) {}
    *(Lisp *head) {}
    
    Clause copy() {
      return new Clause(copy2(head), body == null ? null : body.copy());
    }
    
    public String toString() {
      //ret head + " :- " + (body == null ? "true" : body);
      ret body == null ? head.toString() : head + " :- " + body;
    }
  }

  class Trail {
    Var tcar;
    Trail tcdr;
    
    *(Var *tcar, Trail *tcdr) {}
  }
  
  Trail Trail_Note() { return sofar; }
  void Trail_Push(Var x) { sofar = new Trail(x, sofar); }
  void Trail_Undo(Trail whereto) {
    for (; sofar != whereto; sofar = sofar.tcdr)
      sofar.tcar.reset();
  }
  
  static class TermVarMapping {
    new L<Var> vars;
    
    *(L<Var> *vars) {}
    *(Var... vars) { this.vars.addAll(asList(vars)); }
    
    void showanswer() {
      print("TRUE.");
      for (Var v : vars)
        print("  " + v.getName() + " = " + v);
    }
  }
      
  class Goal {
    Lisp car;
    Goal cdr;
    
    *(Lisp *car, Goal *cdr) {}
    *(Lisp *car) {}
    
    public String toString() {
      ret cdr == null ? car.toString() : car + "; " + cdr;
    }
    
    Goal copy() {
      return new Goal(/* XXX copy2(car) XXX */ Prolog.this.copy(car),
        cdr == null ? null : cdr.copy());
    }
    
    Goal append(Goal l) {
      return new Goal(car, cdr == null ? null : cdr.append(l));
    }
    
  } // class Goal
  
  boolean unify(Lisp thiz, Lisp t) {
    if (thiz == null) fail("thiz=null");
    if (t == null) fail("t=null");
    
    if (thiz instanceof Var) { // TermVar::unify
      Var v = cast thiz;
      if (v.instance != v)
        return unify(v.instance, t);
      Trail_Push(v);
      v.instance = t;
      return true;
    }
    
    // TermCons::unify
    return unify2(t, thiz);
  }
  
  boolean unify2(Lisp thiz, Lisp t) { 
    if (thiz instanceof Var)
      return unify(thiz, t);
   
    int arity = thiz.size();
    if (neq(thiz.head, t.head) || arity != t.size())
      return false;
    for (int i = 0; i < arity; i++)
      if (!unify(thiz.get(i), t.get(i)))
        return false;
    return true;
  }
  
  Lisp copy(Lisp thiz) {
    if (thiz instanceof Var) {
      Var v = cast thiz;
      if (v.instance == v) {
        Trail_Push(v);
        v.instance = newVar();
      }
      return v.instance;
    }
    
    ret copy2(thiz);
  }
  
  Lisp newTermCons(Lisp t) {
    Lisp l = new Lisp(t.head);
    for (Lisp arg : t)
      l.add(copy(arg));
    ret l;
  }
  
  Lisp copy2(Lisp thiz) {
    return newTermCons(thiz);
  }
  
  Var newVar() {
    ret new Var(++varCount);
  }
  
  Var newVar(S name) {
    ret new Var(name);
  }
  
  Clause clause(Lisp head, Goal body) {
    ret prologify(new Clause(head, body));
  }
  
  Clause clause(Lisp rule) {
    L<Lisp> ops = snlSplitOps(rule);
    if (showStuff)
      print("clause(Lisp): " + rule + " => " + structure(ops)); 
      
    if (!empty(ops) && last(ops).is("then *")) {
      Lisp head = last(ops).get(0);
      Goal goal = null;
      
      // TODO: check the actual words (if/and/...)
      for (int i = l(ops)-2; i >= 0; i--)
        goal = new Goal(ops.get(i).get(0), goal);
        
      ret clause(head, goal);
    } else
      ret clause(rule, (Lisp) null);
  }
  
  Clause clause(Lisp head, Lisp body) {
    ret clause(head, body == null ? null : new Goal(body));
  }
  
  Lisp prologify(Lisp term) {
    ret prologify(term, new HashMap);
  }
  
  Clause prologify(Clause c) {
    new HashMap vars;
    c = new Clause(
      prologify(c.head, vars),
      prologify(c.body, vars));
    if (showStuff)
      print("Clause made: " + structure_seen(c));
    ret c;
  }
  
  Goal prologify(Goal goal, Map<S, Var> vars) {
    if (goal == null) ret null;
    ret new Goal(
      prologify(goal.car, vars),
      prologify(goal.cdr, vars));
  }
  
  boolean isVar(Lisp term) {
    ret upperCaseVariables ? snlIsVar(term) : nlIsVar(term);
  }
  
  Lisp prologify(Lisp term, Map<S, Var> vars) {
    if (term == null) ret null;
    if (isVar(term)) {
      Var v = vars.get(term.head);
      if (v == null)
        vars.put(term.head, v = newVar(term.head));
      ret v;
    } else {
      Lisp l = new Lisp(term.head);
      for (Lisp arg : term)
        l.add(prologify(arg, vars));
      ret l;
    }
  }
  
  L<Var> findVars(Goal g) {
    new IdentityHashMap<Var, Boolean> map;
    while (g != null) {
      findVars(g.car, map);
      g = g.cdr;
    }
    ret asList(map.keySet());
  }
  
  L<Var> findVars(Lisp term) {
    new IdentityHashMap<Var, Boolean> map;
    findVars(term, map);
    ret asList(map.keySet());
  }
  
  void findVars(Lisp term, IdentityHashMap<Var, Boolean> map) {
    if (term instanceof Var)
      map.put((Var) term, Boolean.TRUE);
    else
      for (Lisp arg : term)
        findVars(arg, map);
  }
  
  static Map<S, Var> makeVarMap(L<Var> vars) {
    new HashMap<S, Var> map;
    for (Var v : vars)
      map.put(v.getName(), v);
    ret map;
  }
  
  // Executor stack entry
  static class Entry {
    Goal goal;
    int programIdx = -1; // -1 is natives
    Trail trail;
    boolean trailSet;
    boolean cutPoint;
    
    *(Goal *goal) {}
  }
  
  void start(Lisp goal) {
    start(new Goal(prologify(goal)));
  }
  
  // warning: doesn't prologify the goal
  void start(Goal goal) {
    if (showStuff)
      print("start: " + structure_seen(goal));
    steps = 0;
    stack = new L;
    Trail_Undo(null);
    stackAdd(new Entry(goal));
  }
    
  int level() {
    ret l(stack)-1;
  }
  
  boolean done() {
    ret empty(stack);
  }

  boolean gnext(Goal g) {  
    Goal gdash = g.cdr;
    if (gdash == null)
      ret true;
    else {
      stackAdd(new Entry(gdash));
      ret false;
    }
  }
  
  void stackPop() {
    Entry e = popLast(stack);
    if (e.trailSet)
      Trail_Undo(e.trail);
  }
  
  void backToCutPoint() {
    if (showStuff)
      print("back to cut point.");
    while (!empty(stack) && !last(stack).cutPoint) {
      if (showStuff)
        print("cut: dropping " + structure(last(stack)));
      stackPop();
    }
    for (int i = 0; i < 2; i++) {
      if (!empty(stack)) {
        if (showStuff)
          print("cut: dropping " + i + " " + structure(last(stack)));
        stackPop();
      }
    }
  }

  boolean step() {
    if (done()) fail("done!"); // safety
    
    ++steps;
    Entry e = last(stack);
    
    if (e.trailSet) {
      Trail_Undo(e.trail);
      e.trailSet = false;
    }
    
    e.trail = Trail_Note();
    e.trailSet = true;
    
    // cut operator - suceeds first time
    if (e.goal.car.is("!", 0)) {
      if (showStuff)
        print("cut " + e.programIdx + ". " + structure(e.goal));
      if (e.programIdx == -1) {
        ++e.programIdx;
        ret gnext(e.goal);
      } else if (e.programIdx == 0) {
        ++e.programIdx;
        // fails 2nd time and cuts
        //e.goal.car.head = "false"; // super-hack :D
        backToCutPoint();
        ret false;
      } else {
        stackPop();
        ret false;
      }
    }

    if (e.programIdx >= l(program)) { // program loop ends
      removeLast(stack);
      ret false;
    }
      
    if (e.programIdx == -1) {
      if (showStuff)
        print(indent(level()) + "solve@" + level() + ": " + e.goal);
      ++e.programIdx;
        
      // try native functions
      if (goNative(e.goal.car)) {
        if (showStuff)
          print(indent(level()) + "native!");
          
        ret gnext(e.goal);
      }
      
      ret false;
    }
      
    // now in program loop
    
    Clause c = program.get(e.programIdx).copy();
    ++e.programIdx;
    Trail_Undo(e.trail);
    if (showStuff)
      print(indent(level()) + "  try:" + c);
    ++topUnifications;
    if (unify(e.goal.car, c.head)) {
      Goal gdash = c.body == null ? e.goal.cdr : c.body.append(e.goal.cdr);
      if (gdash == null)
        ret true;
      else {
        Entry e2 = new Entry(gdash);
        if (c.body != null)
          e2.cutPoint = true;
        stackAdd(e2);
        ret false;
      }
    } else
      if (showStuff)
        print(indent(level()) + "  nomatch.");
        
    ret false;
  }
  
  void stackAdd(Entry e) {
    stack.add(e);
    int n = l(stack);
    if (n > maxLevelSeen) maxLevelSeen = n;
  }
  
  void addClause(Lisp c) {
    program.add(clause(c));
  }
  
  void addClause(Clause c) {
    program.add(c);
  }
  
  boolean canSolve(Lisp goal) {
    ret canSolve(new Goal(prologify(goal)));
  }
  
  boolean canSolve(Goal goal) {
    start(goal);
    while (!done())
      if (step())
        ret true;
    ret false;
  }
  
  // return variable map or null if unsolved
  Map<S, Lisp> solve(Lisp goal) {
    Goal g = new Goal(prologify(goal));
    if (!canSolve(g))
      ret null;
    ret getUserVarMap();
  }
  
  Map<S, Lisp> getUserVarMap() {
    Goal g = stack.get(0).goal;
    new HashMap<S, Lisp> map;
    for (Var v : findVars(g))
      if (v.isUserVar())
        map.put(v.getName(), v.getValue());
    ret map;
  }
  
  Map<S, Lisp> nextSolution() {
    while (!done())
      if (step())
        ret getUserVarMap();
    ret null;
  }
  
  void addClauses(Lisp tree) {
    if (nlIsMultipleStatements(tree))
      for (Lisp part : tree)
        addClause(part);
    else
      addClause(tree);
  }
  
  boolean goNative(Lisp term) {
    term = resolve(term);
    
    for (Native n : natives) {
      Trail t = Trail_Note();
      boolean result;
      try {
        result = n.yo(this, term);
      } catch (Exception e) {
        Trail_Undo(t);
        continue;
      }
      if (!result) {
        Trail_Undo(t);
        continue;
      }
      ret true;
    }

    if (term.is("nativeTest", 0))
      ret true;
      
    if (term.is("true", 0))
      ret true;
      
    if (term.is("isQuoted", 1)) {
      Lisp x = term.get(0);
      ret !(x instanceof Var) && x.isLeaf() && isQuoted(x.head);
    }
      
    ret false;
  }
  
  // resolve all variables
  Lisp resolve(Lisp term) {
    if (term instanceof Var)
      ret ((Var) term).getValue();
      
    // smart recurse
    for (int i = 0; i < term.size(); i++) {
      Lisp l = term.get(i);
      Lisp r = resolve(l);
      if (l != r) {
        Lisp x = new Lisp(term.head);
        for (int j = 0; j < i; j++)
          x.add(term.get(j));
        x.add(r);
        for (i++; i < term.size(); i++)
          x.add(resolve(term.get(i)));
        ret x;
      }
    }
    
    ret term;
  }
  
  // looks for a bodyless rule in the program that matches the term
  boolean containsStatement(Lisp term) {
    for (Clause c : program)
      if (c.body == null && eq(c.head, term))
        ret true;
    ret false;
  }
  
  // closed == contains no variables
  boolean isClosedTerm(Lisp term) {
    if (term instanceof Var)
      ret false;
    else
      for (Lisp arg : term)
        if (!isClosedTerm(arg))
          ret false;
    ret true;
  }
  
  void addNative(Native n) {
    natives.add(n);
  }
  
  L<Lisp> getStackTerms() {
    new L<Lisp> l;
    for (Entry e : stack)
      l.add(e.goal.car);
    ret l;
  }
  
} // class Prolog

Travelled to 13 computer(s): aoiabmzegqzx, bhatertpkbcr, cbybwowwnfue, cfunsshuasjs, gwrvuhgaqvyk, ishqpsrjomds, lpdgvwnxivlt, mqqgnosmbjvj, pyentgdyhuwx, pzhvpgtvlbxg, tslmcundralx, tvejysmllsmz, vouqrxazstgt

Snippet ID:	#1002826
Snippet name:	class Prolog (old, current in #1002855)
Eternal ID of this version:	#1002826/1
Text MD5:	5c6776886d5283e0f0c53c53c1dcbc39
Author:	stefan
Category:	javax
Type:	JavaX fragment (include)
Public (visible to everyone):	Yes
Archived (hidden from active list):	No
Created/modified:	2016-03-05 17:34:45
Source code size:	12823 bytes / 578 lines
Pitched / IR pitched:	No / No
Views / Downloads:	640 / 819
Referenced in:	[show references]

< > BotCompany Repo | #1002826 // class Prolog (old, current in #1002855)

JavaX fragment (include)

Author comment

1	!752
2
3	static class Prolog {
4	boolean upperCaseVariables = false; // true for SNL, false for NL
5	long varCount;
6	boolean showStuff;
7	new L<Entry> stack;
8	Trail sofar = null;
9	new L<Clause> program;
10	long steps;
11	new L<Native> natives;
12
13	// stats
14	int maxLevelSeen; // maximum stack level reached during computation
15	long topUnifications;
16
17	static interface Native {
18	public boolean yo(Prolog p, Lisp term);
19	}
20
21	static class Var extends Lisp {
22	long id;
23	Lisp instance;
24
25	*(S name) {
26	super(name);
27	instance = this;
28	}
29
30	*(long id) {
31	super("___");
32	this.id = id;
33	instance = this;
34	}
35
36	void reset() { instance = this; }
37
38	public String toString() {
39	if (instance != this)
40	ret instance.toString();
41	ret isUserVar() ? getName() : "_" + id;
42	}
43
44	boolean isUserVar() {
45	ret id == 0;
46	}
47
48	S getName() {
49	ret head;
50	}
51
52	Lisp getValue() {
53	Lisp l = instance;
54	while (l instanceof Var) {
55	Var v = cast l;
56	if (v.instance == v)
57	ret v;
58	l = v.instance;
59	}
60	ret l;
61	}
62	}
63
64	class Clause {
65	Lisp head;
66	Goal body;
67
68	(Lisp head, Goal *body) {}
69	(Lisp head) {}
70
71	Clause copy() {
72	return new Clause(copy2(head), body == null ? null : body.copy());
73	}
74
75	public String toString() {
76	//ret head + " :- " + (body == null ? "true" : body);
77	ret body == null ? head.toString() : head + " :- " + body;
78	}
79	}
80
81	class Trail {
82	Var tcar;
83	Trail tcdr;
84
85	(Var tcar, Trail *tcdr) {}
86	}
87
88	Trail Trail_Note() { return sofar; }
89	void Trail_Push(Var x) { sofar = new Trail(x, sofar); }
90	void Trail_Undo(Trail whereto) {
91	for (; sofar != whereto; sofar = sofar.tcdr)
92	sofar.tcar.reset();
93	}
94
95	static class TermVarMapping {
96	new L<Var> vars;
97
98	(L<Var> vars) {}
99	*(Var... vars) { this.vars.addAll(asList(vars)); }
100
101	void showanswer() {
102	print("TRUE.");
103	for (Var v : vars)
104	print(" " + v.getName() + " = " + v);
105	}
106	}
107
108	class Goal {
109	Lisp car;
110	Goal cdr;
111
112	(Lisp car, Goal *cdr) {}
113	(Lisp car) {}
114
115	public String toString() {
116	ret cdr == null ? car.toString() : car + "; " + cdr;
117	}
118
119	Goal copy() {
120	return new Goal(/* XXX copy2(car) XXX */ Prolog.this.copy(car),
121	cdr == null ? null : cdr.copy());
122	}
123
124	Goal append(Goal l) {
125	return new Goal(car, cdr == null ? null : cdr.append(l));
126	}
127
128	} // class Goal
129
130	boolean unify(Lisp thiz, Lisp t) {
131	if (thiz == null) fail("thiz=null");
132	if (t == null) fail("t=null");
133
134	if (thiz instanceof Var) { // TermVar::unify
135	Var v = cast thiz;
136	if (v.instance != v)
137	return unify(v.instance, t);
138	Trail_Push(v);
139	v.instance = t;
140	return true;
141	}
142
143	// TermCons::unify
144	return unify2(t, thiz);
145	}
146
147	boolean unify2(Lisp thiz, Lisp t) {
148	if (thiz instanceof Var)
149	return unify(thiz, t);
150
151	int arity = thiz.size();
152	if (neq(thiz.head, t.head) \|\| arity != t.size())
153	return false;
154	for (int i = 0; i < arity; i++)
155	if (!unify(thiz.get(i), t.get(i)))
156	return false;
157	return true;
158	}
159
160	Lisp copy(Lisp thiz) {
161	if (thiz instanceof Var) {
162	Var v = cast thiz;
163	if (v.instance == v) {
164	Trail_Push(v);
165	v.instance = newVar();
166	}
167	return v.instance;
168	}
169
170	ret copy2(thiz);
171	}
172
173	Lisp newTermCons(Lisp t) {
174	Lisp l = new Lisp(t.head);
175	for (Lisp arg : t)
176	l.add(copy(arg));
177	ret l;
178	}
179
180	Lisp copy2(Lisp thiz) {
181	return newTermCons(thiz);
182	}
183
184	Var newVar() {
185	ret new Var(++varCount);
186	}
187
188	Var newVar(S name) {
189	ret new Var(name);
190	}
191
192	Clause clause(Lisp head, Goal body) {
193	ret prologify(new Clause(head, body));
194	}
195
196	Clause clause(Lisp rule) {
197	L<Lisp> ops = snlSplitOps(rule);
198	if (showStuff)
199	print("clause(Lisp): " + rule + " => " + structure(ops));
200
201	if (!empty(ops) && last(ops).is("then *")) {
202	Lisp head = last(ops).get(0);
203	Goal goal = null;
204
205	// TODO: check the actual words (if/and/...)
206	for (int i = l(ops)-2; i >= 0; i--)
207	goal = new Goal(ops.get(i).get(0), goal);
208
209	ret clause(head, goal);
210	} else
211	ret clause(rule, (Lisp) null);
212	}
213
214	Clause clause(Lisp head, Lisp body) {
215	ret clause(head, body == null ? null : new Goal(body));
216	}
217
218	Lisp prologify(Lisp term) {
219	ret prologify(term, new HashMap);
220	}
221
222	Clause prologify(Clause c) {
223	new HashMap vars;
224	c = new Clause(
225	prologify(c.head, vars),
226	prologify(c.body, vars));
227	if (showStuff)
228	print("Clause made: " + structure_seen(c));
229	ret c;
230	}
231
232	Goal prologify(Goal goal, Map<S, Var> vars) {
233	if (goal == null) ret null;
234	ret new Goal(
235	prologify(goal.car, vars),
236	prologify(goal.cdr, vars));
237	}
238
239	boolean isVar(Lisp term) {
240	ret upperCaseVariables ? snlIsVar(term) : nlIsVar(term);
241	}
242
243	Lisp prologify(Lisp term, Map<S, Var> vars) {
244	if (term == null) ret null;
245	if (isVar(term)) {
246	Var v = vars.get(term.head);
247	if (v == null)
248	vars.put(term.head, v = newVar(term.head));
249	ret v;
250	} else {
251	Lisp l = new Lisp(term.head);
252	for (Lisp arg : term)
253	l.add(prologify(arg, vars));
254	ret l;
255	}
256	}
257
258	L<Var> findVars(Goal g) {
259	new IdentityHashMap<Var, Boolean> map;
260	while (g != null) {
261	findVars(g.car, map);
262	g = g.cdr;
263	}
264	ret asList(map.keySet());
265	}
266
267	L<Var> findVars(Lisp term) {
268	new IdentityHashMap<Var, Boolean> map;
269	findVars(term, map);
270	ret asList(map.keySet());
271	}
272
273	void findVars(Lisp term, IdentityHashMap<Var, Boolean> map) {
274	if (term instanceof Var)
275	map.put((Var) term, Boolean.TRUE);
276	else
277	for (Lisp arg : term)
278	findVars(arg, map);
279	}
280
281	static Map<S, Var> makeVarMap(L<Var> vars) {
282	new HashMap<S, Var> map;
283	for (Var v : vars)
284	map.put(v.getName(), v);
285	ret map;
286	}
287
288	// Executor stack entry
289	static class Entry {
290	Goal goal;
291	int programIdx = -1; // -1 is natives
292	Trail trail;
293	boolean trailSet;
294	boolean cutPoint;
295
296	(Goal goal) {}
297	}
298
299	void start(Lisp goal) {
300	start(new Goal(prologify(goal)));
301	}
302
303	// warning: doesn't prologify the goal
304	void start(Goal goal) {
305	if (showStuff)
306	print("start: " + structure_seen(goal));
307	steps = 0;
308	stack = new L;
309	Trail_Undo(null);
310	stackAdd(new Entry(goal));
311	}
312
313	int level() {
314	ret l(stack)-1;
315	}
316
317	boolean done() {
318	ret empty(stack);
319	}
320
321	boolean gnext(Goal g) {
322	Goal gdash = g.cdr;
323	if (gdash == null)
324	ret true;
325	else {
326	stackAdd(new Entry(gdash));
327	ret false;
328	}
329	}
330
331	void stackPop() {
332	Entry e = popLast(stack);
333	if (e.trailSet)
334	Trail_Undo(e.trail);
335	}
336
337	void backToCutPoint() {
338	if (showStuff)
339	print("back to cut point.");
340	while (!empty(stack) && !last(stack).cutPoint) {
341	if (showStuff)
342	print("cut: dropping " + structure(last(stack)));
343	stackPop();
344	}
345	for (int i = 0; i < 2; i++) {
346	if (!empty(stack)) {
347	if (showStuff)
348	print("cut: dropping " + i + " " + structure(last(stack)));
349	stackPop();
350	}
351	}
352	}
353
354	boolean step() {
355	if (done()) fail("done!"); // safety
356
357	++steps;
358	Entry e = last(stack);
359
360	if (e.trailSet) {
361	Trail_Undo(e.trail);
362	e.trailSet = false;
363	}
364
365	e.trail = Trail_Note();
366	e.trailSet = true;
367
368	// cut operator - suceeds first time
369	if (e.goal.car.is("!", 0)) {
370	if (showStuff)
371	print("cut " + e.programIdx + ". " + structure(e.goal));
372	if (e.programIdx == -1) {
373	++e.programIdx;
374	ret gnext(e.goal);
375	} else if (e.programIdx == 0) {
376	++e.programIdx;
377	// fails 2nd time and cuts
378	//e.goal.car.head = "false"; // super-hack :D
379	backToCutPoint();
380	ret false;
381	} else {
382	stackPop();
383	ret false;
384	}
385	}
386
387	if (e.programIdx >= l(program)) { // program loop ends
388	removeLast(stack);
389	ret false;
390	}
391
392	if (e.programIdx == -1) {
393	if (showStuff)
394	print(indent(level()) + "solve@" + level() + ": " + e.goal);
395	++e.programIdx;
396
397	// try native functions
398	if (goNative(e.goal.car)) {
399	if (showStuff)
400	print(indent(level()) + "native!");
401
402	ret gnext(e.goal);
403	}
404
405	ret false;
406	}
407
408	// now in program loop
409
410	Clause c = program.get(e.programIdx).copy();
411	++e.programIdx;
412	Trail_Undo(e.trail);
413	if (showStuff)
414	print(indent(level()) + " try:" + c);
415	++topUnifications;
416	if (unify(e.goal.car, c.head)) {
417	Goal gdash = c.body == null ? e.goal.cdr : c.body.append(e.goal.cdr);
418	if (gdash == null)
419	ret true;
420	else {
421	Entry e2 = new Entry(gdash);
422	if (c.body != null)
423	e2.cutPoint = true;
424	stackAdd(e2);
425	ret false;
426	}
427	} else
428	if (showStuff)
429	print(indent(level()) + " nomatch.");
430
431	ret false;
432	}
433
434	void stackAdd(Entry e) {
435	stack.add(e);
436	int n = l(stack);
437	if (n > maxLevelSeen) maxLevelSeen = n;
438	}
439
440	void addClause(Lisp c) {
441	program.add(clause(c));
442	}
443
444	void addClause(Clause c) {
445	program.add(c);
446	}
447
448	boolean canSolve(Lisp goal) {
449	ret canSolve(new Goal(prologify(goal)));
450	}
451
452	boolean canSolve(Goal goal) {
453	start(goal);
454	while (!done())
455	if (step())
456	ret true;
457	ret false;
458	}
459
460	// return variable map or null if unsolved
461	Map<S, Lisp> solve(Lisp goal) {
462	Goal g = new Goal(prologify(goal));
463	if (!canSolve(g))
464	ret null;
465	ret getUserVarMap();
466	}
467
468	Map<S, Lisp> getUserVarMap() {
469	Goal g = stack.get(0).goal;
470	new HashMap<S, Lisp> map;
471	for (Var v : findVars(g))
472	if (v.isUserVar())
473	map.put(v.getName(), v.getValue());
474	ret map;
475	}
476
477	Map<S, Lisp> nextSolution() {
478	while (!done())
479	if (step())
480	ret getUserVarMap();
481	ret null;
482	}
483
484	void addClauses(Lisp tree) {
485	if (nlIsMultipleStatements(tree))
486	for (Lisp part : tree)
487	addClause(part);
488	else
489	addClause(tree);
490	}
491
492	boolean goNative(Lisp term) {
493	term = resolve(term);
494
495	for (Native n : natives) {
496	Trail t = Trail_Note();
497	boolean result;
498	try {
499	result = n.yo(this, term);
500	} catch (Exception e) {
501	Trail_Undo(t);
502	continue;
503	}
504	if (!result) {
505	Trail_Undo(t);
506	continue;
507	}
508	ret true;
509	}
510
511	if (term.is("nativeTest", 0))
512	ret true;
513
514	if (term.is("true", 0))
515	ret true;
516
517	if (term.is("isQuoted", 1)) {
518	Lisp x = term.get(0);
519	ret !(x instanceof Var) && x.isLeaf() && isQuoted(x.head);
520	}
521
522	ret false;
523	}
524
525	// resolve all variables
526	Lisp resolve(Lisp term) {
527	if (term instanceof Var)
528	ret ((Var) term).getValue();
529
530	// smart recurse
531	for (int i = 0; i < term.size(); i++) {
532	Lisp l = term.get(i);
533	Lisp r = resolve(l);
534	if (l != r) {
535	Lisp x = new Lisp(term.head);
536	for (int j = 0; j < i; j++)
537	x.add(term.get(j));
538	x.add(r);
539	for (i++; i < term.size(); i++)
540	x.add(resolve(term.get(i)));
541	ret x;
542	}
543	}
544
545	ret term;
546	}
547
548	// looks for a bodyless rule in the program that matches the term
549	boolean containsStatement(Lisp term) {
550	for (Clause c : program)
551	if (c.body == null && eq(c.head, term))
552	ret true;
553	ret false;
554	}
555
556	// closed == contains no variables
557	boolean isClosedTerm(Lisp term) {
558	if (term instanceof Var)
559	ret false;
560	else
561	for (Lisp arg : term)
562	if (!isClosedTerm(arg))
563	ret false;
564	ret true;
565	}
566
567	void addNative(Native n) {
568	natives.add(n);
569	}
570
571	L<Lisp> getStackTerms() {
572	new L<Lisp> l;
573	for (Entry e : stack)
574	l.add(e.goal.car);
575	ret l;
576	}
577
578	} // class Prolog