src/edu/berkeley/sbp/Parser.java

   1 // Copyright 2006 all rights reserved; see LICENSE file for BSD-style license
   2
   3 package edu.berkeley.sbp;
   4 import edu.berkeley.sbp.*;
   5 import edu.berkeley.sbp.util.*;
   6 import edu.berkeley.sbp.Sequence.Position;
   7 import java.io.*;
   8 import java.util.*;
   9
  10 /** a parser which translates an Input&lt;Token&gt; into a Forest&lt;NodeType&gt; */
  11 public abstract class Parser<Token, NodeType> {
  12     protected final Table<Token> pt;
  13
  14     /** create a parser to parse the grammar with start symbol <tt>u</tt> */
  15     public Parser(Union u, Topology<Token> top)  { this.pt = new Table<Token>(u, top); }
  16     Parser(Table<Token> pt)               { this.pt = pt; }
  17
  18     /** implement this method to create the output forest corresponding to a lone shifted input token */
  19     public abstract Forest<NodeType> shiftToken(Token t, Input.Location newloc);
  20
  21     boolean helpgc = true;
  22
  23     public String toString() { return pt.toString(); }
  24
  25     /** parse <tt>input</tt>, and return the shared packed parse forest (or throw an exception) */
  26     public Forest<NodeType> parse(Input<Token> input) throws IOException, ParseFailed {
  27         GSS gss = new GSS(input);
  28         Input.Location loc = input.getLocation();
  29         Token tok = input.next();
  30         GSS.Phase current = gss.new Phase<Token>(null, null, tok, loc, input.getLocation(), null);
  31         current.newNode(new Result(Forest.create(loc.createRegion(loc), null, null, false), null, null), pt.start, true);
  32         int count = 1;
  33         for(int idx=0;;idx++) {
  34             Input.Location oldloc = loc;
  35             current.reduce();
  36             Forest forest = current.token==null ? null : shiftToken((Token)current.token, loc);
  37             loc = input.getLocation();
  38             Token nextToken = input.next();
  39             GSS.Phase next = gss.new Phase<Token>(current, current, nextToken, loc, input.getLocation(), forest);
  40
  41             /*
  42             FileOutputStream fos = new FileOutputStream("out-"+idx+".dot");
  43             PrintWriter p = new PrintWriter(new OutputStreamWriter(fos));
  44             GraphViz gv = new GraphViz();
  45             for(Object n : current)
  46                 ((Node)n).toGraphViz(gv);
  47             gv.dump(p);
  48             p.flush();
  49             p.close();
  50             */
  51
  52             count = next.size();
  53             if (current.isDone()) return (Forest<NodeType>)gss.finalResult;
  54             current = next;
  55         }
  56     }
  57
  58     // Table //////////////////////////////////////////////////////////////////////////////
  59
  60     /** an SLR(1) parse table which may contain conflicts */
  61     static class Table<Token> extends Walk.Cache {
  62
  63         public String toString() {
  64             StringBuffer sb = new StringBuffer();
  65             sb.append("parse table");
  66             for(State<Token> state : all_states) {
  67                 sb.append("  " + state + "\n");
  68                 for(Topology<Token> t : state.shifts) {
  69                     sb.append("      shift  \""+
  70                               new edu.berkeley.sbp.chr.CharTopology((IntegerTopology<Character>)t)+"\" => ");
  71                     for(State st : state.shifts.getAll(t))
  72                         sb.append(st.idx+"  ");
  73                     sb.append("\n");
  74                 }
  75                 for(Topology<Token> t : state.reductions)
  76                     sb.append("      reduce \""+
  77                               new edu.berkeley.sbp.chr.CharTopology((IntegerTopology<Character>)t)+"\" => " +
  78                               state.reductions.getAll(t) + "\n");
  79                 for(Sequence s : state.gotoSetNonTerminals.keySet())
  80                     sb.append("      goto   "+state.gotoSetNonTerminals.get(s)+" from " + s + "\n");
  81             }
  82             return sb.toString();
  83         }
  84
  85         public final Walk.Cache cache = this;
  86
  87         private void walk(Element e, HashSet<SequenceOrElement> hs) {
  88             if (e==null) return;
  89             if (hs.contains(e)) return;
  90             hs.add(e);
  91             if (e instanceof Atom) return;
  92             for(Sequence s : (Union)e)
  93                 walk(s, hs);
  94         }
  95         private void walk(Sequence s, HashSet<SequenceOrElement> hs) {
  96             hs.add(s);
  97             for(Position p = s.firstp(); p != null; p = p.next())
  98                 walk(p.element(), hs);
  99             for(Sequence ss : s.needs()) walk(ss, hs);
 100             for(Sequence ss : s.hates()) walk(ss, hs);
 101         }
 102
 103         /** the start state */
 104         public  final State<Token>   start;
 105
 106         /** the state from which no reductions can be done */
 107         private final State<Token>   dead_state;
 108
 109         /** used to generate unique values for State.idx */
 110         private int master_state_idx = 0;
 111         HashSet<State<Token>>   all_states    = new HashSet<State<Token>>();
 112         HashMap<HashSet<Position>,State<Token>>   doomed_states    = new HashMap<HashSet<Position>,State<Token>>();
 113         HashMap<HashSet<Position>,State<Token>>   normal_states    = new HashMap<HashSet<Position>,State<Token>>();
 114         HashSet<SequenceOrElement>                all_elements  = new HashSet<SequenceOrElement>();
 115
 116         /** construct a parse table for the given grammar */
 117         public Table(Topology top) { this("s", top); }
 118         public Table(String startSymbol, Topology top) { this(new Union(startSymbol), top); }
 119         public Table(Union ux, Topology top) {
 120             Union start0 = new Union("0");
 121             start0.add(new Sequence.Singleton(ux));
 122
 123             for(Sequence s : start0) cache.eof.put(s, true);
 124             cache.eof.put(start0, true);
 125
 126             // construct the set of states
 127             walk(start0, all_elements);
 128             for(SequenceOrElement e : all_elements)
 129                 cache.ys.addAll(e, new Walk.YieldSet(e, cache).walk());
 130             for(SequenceOrElement e : all_elements)
 131                 cache.ys2.addAll(e, new Walk.YieldSet2(e, cache).walk());
 132             HashSet<Position> hp = new HashSet<Position>();
 133             reachable(start0, hp);
 134
 135             this.dead_state = new State<Token>(new HashSet<Position>(), true);
 136             this.start = new State<Token>(hp);
 137
 138             // for each state, fill in the corresponding "row" of the parse table
 139             for(State<Token> state : all_states)
 140                 for(Position p : state.hs) {
 141
 142                     // the Grammar's designated "last position" is the only accepting state
 143                     if (start0.contains(p.owner()) && p.next()==null && !state.doomed)
 144                         state.accept = true;
 145
 146                     if (isRightNullable(p)) {
 147                         Walk.Follow wf = new Walk.Follow(top.empty(), p.owner(), all_elements, cache);
 148                         Topology follow = wf.walk(p.owner());
 149                         for(Position p2 = p; p2 != null && p2.element() != null; p2 = p2.next()) {
 150                             Atom set = new Walk.EpsilonFollowSet(new edu.berkeley.sbp.chr.CharAtom(top.empty().complement()),
 151                                                                  new edu.berkeley.sbp.chr.CharAtom(top.empty()),
 152                                                                  cache).walk(p2.element());
 153                             follow = follow.intersect(new Walk.Follow(top.empty(), p2.element(), all_elements, cache).walk(p2.element()));
 154                             if (set != null) follow = follow.intersect(set.getTokenTopology());
 155                         }
 156                         state.reductions.put(follow, p);
 157                         if (wf.includesEof()) state.eofReductions.add(p);
 158                     }
 159
 160                     // if the element following this position is an atom, copy the corresponding
 161                     // set of rows out of the "master" goto table and into this state's shift table
 162                     if (p.element() != null && p.element() instanceof Atom)
 163                         state.shifts.addAll(state.gotoSetTerminals.subset(((Atom)p.element()).getTokenTopology()));
 164                 }
 165             if (top instanceof IntegerTopology)
 166                 for(State<Token> state : all_states) {
 167                     state.oreductions = state.reductions.optimize(((IntegerTopology)top).functor());
 168                     state.oshifts = state.shifts.optimize(((IntegerTopology)top).functor());
 169                 }
 170         }
 171
 172         private boolean isRightNullable(Position p) {
 173             if (p.isLast()) return true;
 174             if (!possiblyEpsilon(p.element())) return false;
 175             return isRightNullable(p.next());
 176         }
 177
 178         /** a single state in the LR table and the transitions possible from it */
 179
 180         class State<Token> implements IntegerMappable, Iterable<Position> {
 181
 182             public  final     int               idx    = master_state_idx++;
 183             private final     HashSet<Position> hs;
 184             public HashSet<State<Token>> also = new HashSet<State<Token>>();
 185
 186             public transient HashMap<Sequence,State<Token>>         gotoSetNonTerminals = new HashMap<Sequence,State<Token>>();
 187             private transient TopologicalBag<Token,State<Token>>     gotoSetTerminals    = new TopologicalBag<Token,State<Token>>();
 188
 189             private           TopologicalBag<Token,Position> reductions          = new TopologicalBag<Token,Position>();
 190             private           HashSet<Position>              eofReductions       = new HashSet<Position>();
 191             private           TopologicalBag<Token,State<Token>>     shifts              = new TopologicalBag<Token,State<Token>>();
 192             private           boolean                         accept              = false;
 193
 194             private VisitableMap<Token,State<Token>> oshifts = null;
 195             private VisitableMap<Token,Position> oreductions = null;
 196
 197             // Interface Methods //////////////////////////////////////////////////////////////////////////////
 198
 199             boolean             isAccepting()           { return accept; }
 200             public Iterator<Position>  iterator()       { return hs.iterator(); }
 201
 202             boolean             canShift(Token t)         { return oshifts!=null && oshifts.contains(t); }
 203             <B,C> void          invokeShifts(Token t, Invokable<State<Token>,B,C> irbc, B b, C c) {
 204                 oshifts.invoke(t, irbc, b, c);
 205             }
 206
 207             boolean             canReduce(Token t)        { return oreductions != null && (t==null ? eofReductions.size()>0 : oreductions.contains(t)); }
 208             <B,C> void          invokeReductions(Token t, Invokable<Position,B,C> irbc, B b, C c) {
 209                 if (t==null) for(Position r : eofReductions) irbc.invoke(r, b, c);
 210                 else         oreductions.invoke(t, irbc, b, c);
 211             }
 212
 213             // Constructor //////////////////////////////////////////////////////////////////////////////
 214
 215             /**
 216              *  create a new state consisting of all the <tt>Position</tt>s in <tt>hs</tt>
 217              *  @param hs           the set of <tt>Position</tt>s comprising this <tt>State</tt>
 218              *  @param all_elements the set of all elements (Atom instances need not be included)
 219              *
 220              *   In principle these two steps could be merged, but they
 221              *   are written separately to highlight these two facts:
 222              * <ul>
 223              * <li> Non-atom elements either match all-or-nothing, and do not overlap
 224              *      with each other (at least not in the sense of which element corresponds
 225              *      to the last reduction performed).  Therefore, in order to make sure we
 226              *      wind up with the smallest number of states and shifts, we wait until
 227              *      we've figured out all the token-to-position multimappings before creating
 228              *      any new states
 229              *
 230              * <li> In order to be able to run the state-construction algorithm in a single
 231              *      shot (rather than repeating until no new items appear in any state set),
 232              *      we need to use the "yields" semantics rather than the "produces" semantics
 233              *      for non-Atom Elements.
 234              *  </ul>
 235              */
 236             public State(HashSet<Position> hs) { this(hs, false); }
 237             public boolean doomed;
 238             public State(HashSet<Position> hs, boolean doomed) {
 239                 this.hs = hs;
 240                 this.doomed = doomed;
 241
 242                 // register ourselves in the all_states hash so that no
 243                 // two states are ever created with an identical position set
 244                 ((HashMap)(doomed ? doomed_states : normal_states)).put(hs, this);
 245                 ((HashSet)all_states).add(this);
 246
 247                 for(Position p : hs) {
 248                     if (!p.isFirst()) continue;
 249                     for(Sequence s : p.owner().needs()) {
 250                         if (hs.contains(s.firstp())) continue;
 251                         HashSet<Position> h2 = new HashSet<Position>();
 252                         reachable(s.firstp(), h2);
 253                         also.add(mkstate(h2, true));
 254                     }
 255                     for(Sequence s : p.owner().hates()) {
 256                         if (hs.contains(s.firstp())) continue;
 257                         HashSet<Position> h2 = new HashSet<Position>();
 258                         reachable(s, h2);
 259                         also.add(mkstate(h2, true));
 260                     }
 261                 }
 262
 263                 // Step 1a: examine all Position's in this state and compute the mappings from
 264                 //          sets of follow tokens (tokens which could follow this position) to sets
 265                 //          of _new_ positions (positions after shifting).  These mappings are
 266                 //          collectively known as the _closure_
 267
 268                 TopologicalBag<Token,Position> bag0 = new TopologicalBag<Token,Position>();
 269                 for(Position position : hs) {
 270                     if (position.isLast() || !(position.element() instanceof Atom)) continue;
 271                     Atom a = (Atom)position.element();
 272                     HashSet<Position> hp = new HashSet<Position>();
 273                     reachable(position.next(), hp);
 274                     bag0.addAll(a.getTokenTopology(), hp);
 275                 }
 276
 277                 // Step 1b: for each _minimal, contiguous_ set of characters having an identical next-position
 278                 //          set, add that character set to the goto table (with the State corresponding to the
 279                 //          computed next-position set).
 280
 281                 for(Topology<Token> r : bag0) {
 282                     HashSet<Position> h = new HashSet<Position>();
 283                     for(Position p : bag0.getAll(r)) h.add(p);
 284                     ((TopologicalBag)gotoSetTerminals).put(r, mkstate(h, doomed));
 285                 }
 286
 287                 // Step 2: for every non-Atom element (ie every Element which has a corresponding reduction),
 288                 //         compute the closure over every position in this set which is followed by a symbol
 289                 //         which could yield the Element in question.
 290                 //
 291                 //         "yields" [in one or more step] is used instead of "produces" [in exactly one step]
 292                 //         to avoid having to iteratively construct our set of States as shown in most
 293                 //         expositions of the algorithm (ie "keep doing XYZ until things stop changing").
 294
 295                 HashMapBag<SequenceOrElement,Position> move = new HashMapBag<SequenceOrElement,Position>();
 296                 for(Position p : hs) {
 297                     Element e = p.element();
 298                     if (e==null) continue;
 299                     for(SequenceOrElement y : cache.ys2.getAll(e)) {
 300                         //System.out.println(e + " yields " + y);
 301                         HashSet<Position> hp = new HashSet<Position>();
 302                         reachable(p.next(), hp);
 303                         move.addAll(y, hp);
 304                     }
 305                 }
 306                 OUTER: for(SequenceOrElement y : move) {
 307                     HashSet<Position> h = move.getAll(y);
 308                     State<Token> s = mkstate(h, doomed);
 309                     // if a reduction is "lame", it should wind up in the dead_state after reducing
 310                     if (y instanceof Sequence) {
 311                         for(Position p : hs) {
 312                             if (p.element() != null && (p.element() instanceof Union)) {
 313                                 Union u = (Union)p.element();
 314                                 for(Sequence seq : u)
 315                                     if (seq.needs.contains((Sequence)y) || seq.hates.contains((Sequence)y)) {
 316                                         // FIXME: what if there are two "routes" to get to the sequence?
 317                                         ((HashMap)gotoSetNonTerminals).put((Sequence)y, dead_state);
 318                                         continue OUTER;
 319                                     }
 320                             }
 321                         }
 322                         gotoSetNonTerminals.put((Sequence)y, s);
 323                     }
 324                 }
 325             }
 326
 327             private State<Token> mkstate(HashSet<Position> h, boolean b) {
 328                 if (b) return doomed_states.get(h) == null ? (State)new State<Token>(h,b) : (State)doomed_states.get(h);
 329                 else   return normal_states.get(h) == null ? (State)new State<Token>(h,b) : (State)normal_states.get(h);
 330             }
 331
 332             public String toStringx() {
 333                 StringBuffer st = new StringBuffer();
 334                 for(Position p : this) {
 335                     if (st.length() > 0) st.append("\n");
 336                     st.append(p);
 337                 }
 338                 return st.toString();
 339             }
 340             public String toString() {
 341                 StringBuffer ret = new StringBuffer();
 342                 ret.append("state["+idx+"]: ");
 343                 for(Position p : this) ret.append("{"+p+"}  ");
 344                 return ret.toString();
 345             }
 346
 347             public Walk.Cache cache() { return cache; }
 348             public int toInt() { return idx; }
 349         }
 350     }
 351
 352     // Helpers //////////////////////////////////////////////////////////////////////////////
 353
 354     private static void reachable(Sequence s, HashSet<Position> h) {
 355         reachable(s.firstp(), h);
 356         //for(Sequence ss : s.needs()) reachable(ss, h);
 357         //for(Sequence ss : s.hates()) reachable(ss, h);
 358     }
 359     private static void reachable(Element e, HashSet<Position> h) {
 360         if (e instanceof Atom) return;
 361         for(Sequence s : ((Union)e))
 362             reachable(s, h);
 363     }
 364     private static void reachable(Position p, HashSet<Position> h) {
 365         if (h.contains(p)) return;
 366         h.add(p);
 367         if (p.element() != null) reachable(p.element(), h);
 368     }
 369
 370 }