1 package edu.berkeley.sbp;
2 import edu.berkeley.sbp.*;
3 import edu.berkeley.sbp.util.*;
4 import edu.berkeley.sbp.Sequence.Position;
8 /** a parser which translates streams of Tokens of type T into a Forest<R> */
9 public abstract class Parser<T extends Token, R> {
11 private final Table pt;
13 /** create a parser to parse the grammar with start symbol <tt>u</tt> */
14 protected Parser(Union u) { this.pt = new Table(u, top()); }
15 protected Parser(Table pt) { this.pt = pt; }
17 /** implement this method to create the output forest corresponding to a lone shifted input token */
18 public abstract Forest<R> shiftedToken(T t, Token.Location loc);
20 /** this method must return an empty topology of the input token type */
21 public abstract Topology<T> top();
23 /** parse <tt>input</tt>, using the table <tt>pt</tt> to drive the parser */
24 public Forest<R> parse(Token.Stream<T> input) throws IOException, ParseFailed {
26 Token.Location loc = input.getLocation();
27 GSS.Phase current = gss.new Phase(null, this, null, input.next(1, 0, 0), loc, null);
28 current.newNode(null, Forest.leaf(null, null), pt.start, true);
31 loc = input.getLocation();
33 Forest forest = current.token==null ? null : shiftedToken((T)current.token, loc);
34 GSS.Phase next = gss.new Phase(current, this, current, input.next(count, gss.resets, gss.waits), loc, forest);
36 if (current.isDone()) return (Forest<R>)gss.finalResult;
41 // Table //////////////////////////////////////////////////////////////////////////////
43 /** an SLR(1) parse table which may contain conflicts */
44 static class Table extends Walk.Cache {
46 public final Walk.Cache cache = this;
48 private void walk(Element e, HashSet<Element> hs) {
50 if (hs.contains(e)) return;
52 if (e instanceof Atom) return;
53 for(Sequence s : (Union)e) {
55 for(Position p = s.firstp(); p != null; p = p.next())
56 walk(p.element(), hs);
60 /** the start state */
61 public final State start;
63 /** used to generate unique values for State.idx */
64 private int master_state_idx = 0;
66 /** construct a parse table for the given grammar */
67 public Table(Topology top) { this("s", top); }
68 public Table(String startSymbol, Topology top) { this(new Union(startSymbol), top); }
69 public Table(Union ux, Topology top) {
70 Union start0 = new Union("0");
71 start0.add(new Sequence.Singleton(ux, null, null));
73 for(Sequence s : start0) cache.eof.put(s, true);
74 cache.eof.put(start0, true);
76 // construct the set of states
77 HashMap<HashSet<Position>,State> all_states = new HashMap<HashSet<Position>,State>();
78 HashSet<Element> all_elements = new HashSet<Element>();
79 walk(start0, all_elements);
80 for(Element e : all_elements)
81 cache.ys.addAll(e, new Walk.YieldSet(e, cache).walk());
82 HashSet<Position> hp = new HashSet<Position>();
83 reachable(start0, hp);
84 this.start = new State(hp, all_states, all_elements);
86 // for each state, fill in the corresponding "row" of the parse table
87 for(State state : all_states.values())
88 for(Position p : state.hs) {
90 // the Grammar's designated "last position" is the only accepting state
91 if (start0.contains(p.owner()) && p.next()==null)
94 if (isRightNullable(p)) {
95 Walk.Follow wf = new Walk.Follow(top.empty(), p.owner(), all_elements, cache);
96 Reduction red = new Reduction(p);
98 Topology follow = wf.walk(p.owner());
99 for(Position p2 = p; p2 != null && p2.element() != null; p2 = p2.next())
100 follow = follow.intersect(new Walk.Follow(top.empty(), p2.element(), all_elements, cache).walk(p2.element()));
101 state.reductions.put(follow, red);
102 if (wf.includesEof()) state.eofReductions.add(red);
105 // if the element following this position is an atom, copy the corresponding
106 // set of rows out of the "master" goto table and into this state's shift table
107 if (p.element() != null && p.element() instanceof Atom)
108 state.shifts.addAll(state.gotoSetTerminals.subset(((Atom)p.element())));
110 for(State state : all_states.values()) {
111 state.oreductions = state.reductions.optimize();
112 state.oshifts = state.shifts.optimize();
116 private boolean isRightNullable(Position p) {
117 if (p.isLast()) return true;
118 if (!p.element().possiblyEpsilon(this)) return false;
119 return isRightNullable(p.next());
122 /** a single state in the LR table and the transitions possible from it */
124 public class State implements Comparable<Table.State>, IntegerMappable, Iterable<Position> {
126 public final int idx = master_state_idx++;
127 private final HashSet<Position> hs;
129 public transient HashMap<Element,State> gotoSetNonTerminals = new HashMap<Element,State>();
130 private transient TopologicalBag<Token,State> gotoSetTerminals = new TopologicalBag<Token,State>();
132 private TopologicalBag<Token,Reduction> reductions = new TopologicalBag<Token,Reduction>();
133 private HashSet<Reduction> eofReductions = new HashSet<Reduction>();
134 private TopologicalBag<Token,State> shifts = new TopologicalBag<Token,State>();
135 private boolean accept = false;
137 private VisitableMap<Token,State> oshifts = null;
138 private VisitableMap<Token,Reduction> oreductions = null;
140 // Interface Methods //////////////////////////////////////////////////////////////////////////////
142 boolean isAccepting() { return accept; }
143 public Iterator<Position> iterator() { return hs.iterator(); }
145 boolean canShift(Token t) { return oshifts.contains(t); }
146 <B,C> void invokeShifts(Token t, Invokable<State,B,C> irbc, B b, C c) {
147 oshifts.invoke(t, irbc, b, c);
150 boolean canReduce(Token t) { return t==null ? eofReductions.size()>0 : oreductions.contains(t); }
151 <B,C> void invokeReductions(Token t, Invokable<Reduction,B,C> irbc, B b, C c) {
152 if (t==null) for(Reduction r : eofReductions) irbc.invoke(r, b, c);
153 else oreductions.invoke(t, irbc, b, c);
156 // Constructor //////////////////////////////////////////////////////////////////////////////
159 * create a new state consisting of all the <tt>Position</tt>s in <tt>hs</tt>
160 * @param hs the set of <tt>Position</tt>s comprising this <tt>State</tt>
161 * @param all_states the set of states already constructed (to avoid recreating states)
162 * @param all_elements the set of all elements (Atom instances need not be included)
164 * In principle these two steps could be merged, but they
165 * are written separately to highlight these two facts:
167 * <li> Non-atom elements either match all-or-nothing, and do not overlap
168 * with each other (at least not in the sense of which element corresponds
169 * to the last reduction performed). Therefore, in order to make sure we
170 * wind up with the smallest number of states and shifts, we wait until
171 * we've figured out all the token-to-position multimappings before creating
174 * <li> In order to be able to run the state-construction algorithm in a single
175 * shot (rather than repeating until no new items appear in any state set),
176 * we need to use the "yields" semantics rather than the "produces" semantics
177 * for non-Atom Elements.
180 public State(HashSet<Position> hs,
181 HashMap<HashSet<Position>,State> all_states,
182 HashSet<Element> all_elements) {
185 // register ourselves in the all_states hash so that no
186 // two states are ever created with an identical position set
187 all_states.put(hs, this);
189 // Step 1a: examine all Position's in this state and compute the mappings from
190 // sets of follow tokens (tokens which could follow this position) to sets
191 // of _new_ positions (positions after shifting). These mappings are
192 // collectively known as the _closure_
194 TopologicalBag<Token,Position> bag0 = new TopologicalBag<Token,Position>();
195 for(Position position : hs) {
196 if (position.isLast() || !(position.element() instanceof Atom)) continue;
197 Atom a = (Atom)position.element();
198 HashSet<Position> hp = new HashSet<Position>();
199 reachable(position.next(), hp);
203 // Step 1b: for each _minimal, contiguous_ set of characters having an identical next-position
204 // set, add that character set to the goto table (with the State corresponding to the
205 // computed next-position set).
207 for(Topology<Token> r : bag0) {
208 HashSet<Position> h = new HashSet<Position>();
209 for(Position p : bag0.getAll(r)) h.add(p);
210 gotoSetTerminals.put(r, all_states.get(h) == null ? new State(h, all_states, all_elements) : all_states.get(h));
213 // Step 2: for every non-Atom element (ie every Element which has a corresponding reduction),
214 // compute the closure over every position in this set which is followed by a symbol
215 // which could yield the Element in question.
217 // "yields" [in one or more step] is used instead of "produces" [in exactly one step]
218 // to avoid having to iteratively construct our set of States as shown in most
219 // expositions of the algorithm (ie "keep doing XYZ until things stop changing").
220 HashMapBag<Element,Position> move = new HashMapBag<Element,Position>();
221 for(Position p : hs) {
222 Element e = p.element();
223 if (e==null) continue;
224 for(Element y : cache.ys.getAll(e)) {
225 HashSet<Position> hp = new HashSet<Position>();
226 reachable(p.next(), hp);
230 for(Element y : move) {
231 HashSet<Position> h = move.getAll(y);
232 State s = all_states.get(h) == null ? new State(h, all_states, all_elements) : all_states.get(h);
233 gotoSetNonTerminals.put(y, s);
237 public String toString() {
238 StringBuffer ret = new StringBuffer();
239 ret.append("state["+idx+"]: ");
240 for(Position p : this) ret.append("{"+p+"} ");
241 return ret.toString();
244 public int compareTo(Table.State s) { return idx==s.idx ? 0 : idx < s.idx ? -1 : 1; }
245 public int toInt() { return idx; }
249 * the information needed to perform a reduction; copied here to
250 * avoid keeping references to <tt>Element</tt> objects in a Table
252 public class Reduction {
253 // FIXME: cleanup; almost everything in here could go in either Sequence.Position.getRewrite() or else in GSS.Reduct
254 /*private*/ final Position position;
255 public int hashCode() { return position.hashCode(); }
256 public boolean equals(Object o) {
257 if (o==null) return false;
258 if (o==this) return true;
259 if (!(o instanceof Reduction)) return false;
260 Reduction r = (Reduction)o;
261 return r.position == position;
263 public Reduction(Position p) {
266 public String toString() { return "[reduce " + position + "]"; }
268 private Forest zero = null;
269 public Forest zero() {
270 if (zero != null) return zero;
271 if (position.pos > 0) throw new Error();
272 return zero = position.rewrite(null);
275 // FIXME: this could be more elegant and/or cleaner and/or somewhere else
276 public void reduce(GSS.Phase.Node parent, int pos, GSS.Phase target, Forest[] holder) {
277 Forest old = holder[pos];
278 holder[pos] = parent.pending();
280 System.arraycopy(holder, 0, position.holder, 0, holder.length);
281 for(int i=0; i<position.pos; i++) if (position.holder[i]==null) throw new Error("realbad");
282 Forest rex = position.rewrite(target.getLocation());
283 for(GSS.Phase.Node child : parent.parents()) child.finish(this, rex, target, holder);
285 for(GSS.Phase.Node child : parent.parents()) reduce(child, pos-1, target, holder);
292 private static final Forest[] emptyForestArray = new Forest[0];
295 // Helpers //////////////////////////////////////////////////////////////////////////////
297 private static void reachable(Element e, HashSet<Position> h) {
298 if (e instanceof Atom) return;
299 for(Sequence s : ((Union)e))
300 reachable(s.firstp(), h);
302 private static void reachable(Position p, HashSet<Position> h) {
303 if (h.contains(p)) return;
305 if (p.element() != null) reachable(p.element(), h);