X-Git-Url: http://git.megacz.com/?p=sbp.git;a=blobdiff_plain;f=src%2Fedu%2Fberkeley%2Fsbp%2FParser.java;h=2344e15b96c2cb9f451c27f248edc3e04c15978f;hp=d4d5415972c984141db742da684e523a41e4736d;hb=ae0cef03f2e46f6ae6438f9a3e60ca36ff1a4643;hpb=24112db237318c030b4d4f457d90c34fd69d652b

diff --git a/src/edu/berkeley/sbp/Parser.java b/src/edu/berkeley/sbp/Parser.java
index d4d5415..2344e15 100644
--- a/src/edu/berkeley/sbp/Parser.java
+++ b/src/edu/berkeley/sbp/Parser.java
@@ -94,7 +94,10 @@ public abstract class Parser<Tok, Result> {
         }
 
         /** the start state */
-        public final State<Tok>   start;
+        public  final State<Tok>   start;
+
+        /** the state from which no reductions can be done */
+        private final State<Tok>   dead_state;
 
         /** used to generate unique values for State.idx */
         private int master_state_idx = 0;
@@ -117,6 +120,8 @@ public abstract class Parser<Tok, Result> {
                 cache.ys.addAll(e, new Walk.YieldSet(e, cache).walk());
             HashSet<Position> hp = new HashSet<Position>();
             reachable(start0, hp);
+
+            this.dead_state = new State<Tok>(new HashSet<Position>(), all_states, all_elements);
             this.start = new State<Tok>(hp, all_states, all_elements);
 
             // for each state, fill in the corresponding "row" of the parse table
@@ -174,15 +179,15 @@ public abstract class Parser<Tok, Result> {
 
             // Interface Methods //////////////////////////////////////////////////////////////////////////////
 
-            boolean             isAccepting()               { return accept; }
-            public Iterator<Position>  iterator()                  { return hs.iterator(); }
+            boolean             isAccepting()           { return accept; }
+            public Iterator<Position>  iterator()       { return hs.iterator(); }
 
-            boolean             canShift(Tok t)           { return oshifts.contains(t); }
+            boolean             canShift(Tok t)         { return oshifts!=null && oshifts.contains(t); }
             <B,C> void          invokeShifts(Tok t, Invokable<State<Tok>,B,C> irbc, B b, C c) {
                 oshifts.invoke(t, irbc, b, c);
             }
 
-            boolean             canReduce(Tok t)          { return t==null ? eofReductions.size()>0 : oreductions.contains(t); }
+            boolean             canReduce(Tok t)        { return oreductions != null && (t==null ? eofReductions.size()>0 : oreductions.contains(t)); }
             <B,C> void          invokeReductions(Tok t, Invokable<Position,B,C> irbc, B b, C c) {
                 if (t==null) for(Position r : eofReductions) irbc.invoke(r, b, c);
                 else         oreductions.invoke(t, irbc, b, c);
@@ -252,6 +257,7 @@ public abstract class Parser<Tok, Result> {
                 //         "yields" [in one or more step] is used instead of "produces" [in exactly one step]
                 //         to avoid having to iteratively construct our set of States as shown in most
                 //         expositions of the algorithm (ie "keep doing XYZ until things stop changing").
+
                 HashMapBag<Element,Position> move = new HashMapBag<Element,Position>();
                 for(Position p : hs) {
                     Element e = p.element();
@@ -265,7 +271,11 @@ public abstract class Parser<Tok, Result> {
                 for(Element y : move) {
                     HashSet<Position> h = move.getAll(y);
                     State<Tok> s = all_states.get(h) == null ? new State<Tok>(h, all_states, all_elements) : all_states.get(h);
-                    gotoSetNonTerminals.put(y, s);
+                    // if a reduction is "lame", it should wind up in the dead_state after reducing
+                    if (y instanceof Sequence && ((Sequence)y).lame)
+                        ((HashMap)gotoSetNonTerminals).put(y, dead_state);
+                    else
+                        gotoSetNonTerminals.put(y, s);
                 }
             }