// Copyright 2006 all rights reserved; see LICENSE file for BSD-style license
package edu.berkeley.sbp;
-import edu.berkeley.sbp.*;
import edu.berkeley.sbp.util.*;
import edu.berkeley.sbp.Sequence.Position;
import java.io.*;
import java.util.*;
+// FEATURE: try harder to "fuse" states together along two dimensions:
+// - identical (equivalent) states, or states that subsume each other
+// - unnecessary intermediate states ("short cut" GLR)
+
/** a parser which translates an Input<Token> into a Forest<NodeType> */
public abstract class Parser<Token, NodeType> {
- protected final Table<Token> pt;
+ final Table pt;
/** create a parser to parse the grammar with start symbol <tt>u</tt> */
- public Parser(Union u, Topology<Token> top) { this.pt = new Table<Token>(u, top); }
+ public Parser(Union u) { this.pt = new Table(u); }
/** implement this method to create the output forest corresponding to a lone shifted input token */
- public abstract Forest<NodeType> shiftToken(Token t, Input.Location newloc);
+ public abstract Forest<NodeType> shiftToken(Token t, Input.Region region);
- public String toString() { return pt.toString(); }
+ public abstract Topology<Token> emptyTopology();
- private boolean verbose = false;;
- private static final char[] spin = new char[] { '-', '\\', '|', '/' };
- private int spinpos = 0;
- private long last = 0;
- void spin() {
- if (verbose) {
- long now = System.currentTimeMillis();
- if (now-last < 70) return;
- last = now;
- System.err.print("\r " + spin[spinpos++ % (spin.length)]+ANSI.clreol()+"\r");
- }
- }
+ public String toString() { return pt.toString(); }
+ Cache cache() { return pt; }
/** parse <tt>input</tt>, and return the shared packed parse forest (or throw an exception) */
public Forest<NodeType> parse(Input<Token> input) throws IOException, ParseFailed {
for(GSS.Phase current = gss.new Phase<Token>(pt.start); ;) {
if (verbose) {
+ // FIXME: clean this up
String s;
s = " " + spin[spinpos++ % (spin.length)]+" parsing ";
s += input.getName();
String y = "@"+gss.viewPos+" ";
while(y.length() < 9) y = " " + y;
s += y;
- //s += " doom="+Node.doomedNodes;
- //while(s.length() < 40) s = s + " ";
s += " nodes="+gss.numOldNodes;
while(s.length() < 50) s = s + " ";
s += " shifted="+gss.numNewNodes;
System.err.print("\r"+s+ANSI.clreol()+"\r");
}
- // FIXME: make sure all the locations line up properly in here
if (current.isDone()) return (Forest<NodeType>)current.finalResult;
- Forest forest = shiftToken((Token)current.token, input.getLocation());
+ Forest forest = shiftToken((Token)current.token, current.getRegion());
current = gss.new Phase<Token>(current, forest);
}
- } finally {
- if (verbose)
- System.err.print("\r \r");
- }
+ } finally { if (verbose) System.err.print("\r"+ANSI.clreol()); }
}
+ // Spinner //////////////////////////////////////////////////////////////////////////////
+
+ private boolean verbose = false;
+ private static final char[] spin = new char[] { '-', '\\', '|', '/' };
+ private int spinpos = 0;
+ private long last = 0;
+ void spin() {
+ if (!verbose) return;
+ long now = System.currentTimeMillis();
+ if (now-last < 70) return;
+ last = now;
+ System.err.print("\r " + spin[spinpos++ % (spin.length)]+"\r");
+ }
// Table //////////////////////////////////////////////////////////////////////////////
/** an SLR(1) parse table which may contain conflicts */
- static class Table<Token> extends Cache {
+ class Table extends Cache<Token> {
/** the start state */
- public final State<Token> start;
+ final State<Token> start;
- /** the state from which no reductions can be done */
+ /** a dummy state from which no reductions can be performed */
private final State<Token> dead_state;
/** used to generate unique values for State.idx */
private int master_state_idx = 0;
- HashSet<State<Token>> all_states = new HashSet<State<Token>>();
+
+ /** all the states for this table */
+ HashSet<State<Token>> all_states = new HashSet<State<Token>>();
+
+ /** all the doomed states in this table */
HashMap<HashSet<Position>,State<Token>> doomed_states = new HashMap<HashSet<Position>,State<Token>>();
+
+ /** all the non-doomed states in this table */
HashMap<HashSet<Position>,State<Token>> normal_states = new HashMap<HashSet<Position>,State<Token>>();
+ Topology<Token> emptyTopology() { return Parser.this.emptyTopology(); }
+
/** construct a parse table for the given grammar */
- public Table(Topology top) { this("s", top); }
- public Table(String startSymbol, Topology top) { this(new Union(startSymbol), top); }
- public Table(Union ux, Topology top) {
- super(ux, top);
- Union start0 = new Union("0");
- Sequence seq0 = new Sequence.Singleton(ux);
- start0.add(seq0);
- buildFollowSet(seq0, top, true);
-
- // construct the set of states
- HashSet<Position> hp = new HashSet<Position>();
- reachable(start0, hp);
+ Table(Union ux) {
+ super(new Union("0", Sequence.create(ux), true));
+ // create the "dead state"
this.dead_state = new State<Token>(new HashSet<Position>(), true);
- this.start = new State<Token>(hp);
+ // construct the start state; this will recursively create *all* the states
+ this.start = new State<Token>(reachable(rootUnion), false);
+
+ buildReductions();
+ sortReductions();
+ }
+
+ /** fill in the reductions table */
+ private void buildReductions() {
// for each state, fill in the corresponding "row" of the parse table
for(State<Token> state : all_states)
for(Position p : state.hs) {
- // the Grammar's designated "last position" is the only accepting state
- if (start0.contains(p.owner()) && p.next()==null && !state.doomed)
- state.accept = true;
-
- if (isRightNullable(p)) {
- Topology<Token> follow = (Topology<Token>)follow(p.owner());
- for(Position p2 = p; p2 != null && p2.element() != null; p2 = p2.next()) {
- if (!(p2.element() instanceof Union)) throw new Error("impossible");
- Union u = (Union)p2.element();
- Atom set = new edu.berkeley.sbp.chr.CharAtom(new edu.berkeley.sbp.chr.CharTopology((Topology<Character>)epsilonFollowSet(u)));
- Element p2e = p2.element();
- if (p2e instanceof Union)
- for(Sequence p2es : ((Union)p2e))
- follow = follow.intersect(follow(p2es));
- if (set != null) follow = follow.intersect(set.getTokenTopology());
- }
- state.reductions.put(follow, p);
- if (followEof.contains(p.owner())) state.eofReductions.add(p);
- }
-
// if the element following this position is an atom, copy the corresponding
// set of rows out of the "master" goto table and into this state's shift table
if (p.element() != null && p.element() instanceof Atom)
state.shifts.addAll(state.gotoSetTerminals.subset(((Atom)p.element()).getTokenTopology()));
+
+ // RNGLR: we can potentially reduce from any "right-nullable" position -- that is,
+ // any position for which all Elements after it in the Sequence are capable of
+ // matching the empty string.
+ if (!isRightNullable(p)) continue;
+ Topology<Token> follow = follow(p.owner());
+ for(Position p2 = p; p2 != null && p2.element() != null; p2 = p2.next()) {
+ if (!(p2.element() instanceof Union))
+ throw new Error("impossible -- only Unions can be nullable");
+
+ // interesting RNGLR-followRestriction interaction: we must intersect
+ // not just the follow-set of the last non-nullable element, but the
+ // follow-sets of the nulled elements as well.
+ for(Sequence s : ((Union)p2.element()))
+ follow = follow.intersect(follow(s));
+ Topology<Token> set = epsilonFollowSet((Union)p2.element());
+ if (set != null) follow = follow.intersect(set);
+ }
+
+ // indicate that when the next token is in the set "follow", nodes in this
+ // state should reduce according to Position "p"
+ state.reductions.put(follow, p);
+ if (followEof.contains(p.owner())) state.eofReductions.add(p);
}
- if (top instanceof IntegerTopology)
+ // optimize the reductions table
+ if (emptyTopology() instanceof IntegerTopology)
for(State<Token> state : all_states) {
- state.oreductions = state.reductions.optimize(((IntegerTopology)top).functor());
- state.oshifts = state.shifts.optimize(((IntegerTopology)top).functor());
+ // FIXME: this is pretty ugly
+ state.oreductions = state.reductions.optimize(((IntegerTopology)emptyTopology()).functor());
+ state.oshifts = state.shifts.optimize(((IntegerTopology)emptyTopology()).functor());
}
+ }
+ // FIXME: this method needs to be cleaned up and documented
+ private void sortReductions() {
// crude algorithm to assing an ordinal ordering to every position
// al will be sorted in DECREASING order (al[0] >= al[1])
ArrayList<Sequence.Position> al = new ArrayList<Sequence.Position>();
}
al.get(i).ord = j;
}
-
- /*
- for(int i=0; i<al.size(); i++)
- if (isRightNullable(al.get(i)))
- System.out.println(al.get(i).ord + " " + al.get(i));
- */
- //mastercache = this;
}
- /** a single state in the LR table and the transitions possible from it */
+ /**
+ * A single state in the LR table and the transitions
+ * possible from it
+ *
+ * A state corresponds to a set of Sequence.Position's. Each
+ * Node in the GSS has a State; the Node represents a set of
+ * possible parses, one for each Position in the State.
+ *
+ * Every state is either "doomed" or "normal". If a Position
+ * is part of a Sequence which is a conjunct (that is, it was
+ * passed to Sequence.{and(),andnot()}), then that Position
+ * will appear only in doomed States. Furthermore, any set
+ * of Positions reachable from a doomed State also forms a
+ * doomed State. Note that in this latter case, a doomed
+ * state might have exactly the same set of Positions as a
+ * non-doomed state.
+ *
+ * Nodes with non-doomed states represent nodes which
+ * contribute to actual valid parses. Nodes with doomed
+ * States exist for no other purpose than to enable/disable
+ * some future reduction from a non-doomed Node. Because of
+ * this, we "garbage-collect" Nodes with doomed states if
+ * there are no more non-doomed Nodes which they could
+ * affect (see Result, Reduction, and Node for details).
+ *
+ * Without this optimization, many seemingly-innocuous uses
+ * of positive and negative conjuncts can trigger O(n^2)
+ * space+time complexity in otherwise simple grammars. There
+ * is an example of this in the regression suite.
+ */
class State<Token> implements IntegerMappable, Iterable<Position> {
public final int idx = master_state_idx++;
private final HashSet<Position> hs;
- public HashSet<State<Token>> also = new HashSet<State<Token>>();
+ public HashSet<State<Token>> conjunctStates = new HashSet<State<Token>>();
- public transient HashMap<Sequence,State<Token>> gotoSetNonTerminals = new HashMap<Sequence,State<Token>>();
- private transient TopologicalBag<Token,State<Token>> gotoSetTerminals = new TopologicalBag<Token,State<Token>>();
+ HashMap<Sequence,State<Token>> gotoSetNonTerminals = new HashMap<Sequence,State<Token>>();
+ private transient TopologicalBag<Token,State<Token>> gotoSetTerminals = new TopologicalBag<Token,State<Token>>();
private TopologicalBag<Token,Position> reductions = new TopologicalBag<Token,Position>();
private HashSet<Position> eofReductions = new HashSet<Position>();
private VisitableMap<Token,State<Token>> oshifts = null;
private VisitableMap<Token,Position> oreductions = null;
+ public final boolean doomed;
// Interface Methods //////////////////////////////////////////////////////////////////////////////
else oreductions.invoke(t, node, null);
}
void invokeReductions(Token t, Node node, Result b) {
- //System.err.println("\rinvokage: " + this);
if (t==null) for(Position r : eofReductions) node.invoke(r, b);
else oreductions.invoke(t, node, b);
}
* for non-Atom Elements.
* </ul>
*/
- public State(HashSet<Position> hs) { this(hs, false); }
- public boolean doomed;
public State(HashSet<Position> hs, boolean doomed) {
this.hs = hs;
this.doomed = doomed;
- // register ourselves in the all_states hash so that no
- // two states are ever created with an identical position set
+ // register ourselves so that no two states are ever
+ // created with an identical position set (termination depends on this)
((HashMap)(doomed ? doomed_states : normal_states)).put(hs, this);
((HashSet)all_states).add(this);
-
+
for(Position p : hs) {
+ // Step 1a: take note if we are an accepting state
+ // (last position of the root Union's sequence)
+ if (p.next()==null && !doomed && rootUnion.contains(p.owner()))
+ accept = true;
+
+ // Step 1b: If any Position in the set is the first position of its sequence, then this
+ // state is responsible for spawning the "doomed" states for each of the
+ // Sequence's conjuncts. This obligation is recorded by adding the to-be-spawned
+ // states to conjunctStates.
if (!p.isFirst()) continue;
- for(Sequence s : p.owner().needs()) {
- if (hs.contains(s.firstp())) continue;
- HashSet<Position> h2 = new HashSet<Position>();
- reachable(s, h2);
- also.add(mkstate(h2, true));
- }
- for(Sequence s : p.owner().hates()) {
- if (hs.contains(s.firstp())) continue;
- HashSet<Position> h2 = new HashSet<Position>();
- reachable(s, h2);
- also.add(mkstate(h2, true));
- }
+ for(Sequence s : p.owner().needs())
+ if (!hs.contains(s.firstp()))
+ conjunctStates.add(mkstate(reachable(s.firstp()), true));
+ for(Sequence s : p.owner().hates())
+ if (!hs.contains(s.firstp()))
+ conjunctStates.add(mkstate(reachable(s.firstp()), true));
}
- // Step 1a: examine all Position's in this state and compute the mappings from
+ // Step 2a: examine all Position's in this state and compute the mappings from
// sets of follow tokens (tokens which could follow this position) to sets
// of _new_ positions (positions after shifting). These mappings are
// collectively known as the _closure_
bag0.addAll(a.getTokenTopology(), hp);
}
- // Step 1b: for each _minimal, contiguous_ set of characters having an identical next-position
+ // Step 2b: for each _minimal, contiguous_ set of characters having an identical next-position
// set, add that character set to the goto table (with the State corresponding to the
// computed next-position set).
((TopologicalBag)gotoSetTerminals).put(r, mkstate(h, doomed));
}
- // Step 2: for every Sequence, compute the closure over every position in this set which
+ // Step 3: for every Sequence, compute the closure over every position in this set which
// is followed by a symbol which could yield the Sequence.
//
// "yields" [in one or more step] is used instead of "produces" [in exactly one step]
}
private State<Token> mkstate(HashSet<Position> h, boolean b) {
- if (b) return doomed_states.get(h) == null ? (State)new State<Token>(h,b) : (State)doomed_states.get(h);
- else return normal_states.get(h) == null ? (State)new State<Token>(h,b) : (State)normal_states.get(h);
- }
-
- public String toStringx() {
- StringBuffer st = new StringBuffer();
- for(Position p : this) {
- if (st.length() > 0) st.append("\n");
- st.append(p);
- }
- return st.toString();
- }
-
- public String toString() {
- StringBuffer ret = new StringBuffer();
- ret.append("state["+idx+"]: ");
- for(Position p : this) ret.append("{"+p+"} ");
- return ret.toString();
+ State ret = (b?doomed_states:normal_states).get(h);
+ if (ret==null) ret = new State<Token>(h,b);
+ return ret;
}
public int toInt() { return idx; }
}
- public String toString() {
- StringBuffer sb = new StringBuffer();
- sb.append("parse table");
- for(State<Token> state : all_states) {
- sb.append(" " + state + "\n");
- for(Topology<Token> t : state.shifts) {
- sb.append(" shift \""+
- new edu.berkeley.sbp.chr.CharTopology((IntegerTopology<Character>)t)+"\" => ");
- for(State st : state.shifts.getAll(t))
- sb.append(st.idx+" ");
- sb.append("\n");
- }
- for(Topology<Token> t : state.reductions)
- sb.append(" reduce \""+
- new edu.berkeley.sbp.chr.CharTopology((IntegerTopology<Character>)t)+"\" => " +
- state.reductions.getAll(t) + "\n");
- for(Sequence s : state.gotoSetNonTerminals.keySet())
- sb.append(" goto "+state.gotoSetNonTerminals.get(s)+" from " + s + "\n");
- }
- return sb.toString();
- }
}
// Helpers //////////////////////////////////////////////////////////////////////////////
- private static void reachable(Sequence s, HashSet<Position> h) {
- reachable(s.firstp(), h);
- //for(Sequence ss : s.needs()) reachable(ss, h);
- //for(Sequence ss : s.hates()) reachable(ss, h);
+ private static HashSet<Position> reachable(Element e) {
+ HashSet<Position> h = new HashSet<Position>();
+ reachable(e, h);
+ return h;
}
private static void reachable(Element e, HashSet<Position> h) {
if (e instanceof Atom) return;
for(Sequence s : ((Union)e))
- reachable(s, h);
+ reachable(s.firstp(), h);
}
private static void reachable(Position p, HashSet<Position> h) {
if (h.contains(p)) return;
h.add(p);
if (p.element() != null) reachable(p.element(), h);
}
- //public static Cache mastercache = null;
+ private static HashSet<Position> reachable(Position p) {
+ HashSet<Position> ret = new HashSet<Position>();
+ reachable(p, ret);
+ return ret;
+ }
+
}
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