X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=src%2Fedu%2Fberkeley%2Fsbp%2FSequence.java;h=ac34264b3a527fe16c9fb6790ab802e4aab2840d;hb=f7f669e438822dd46922e3d3b1c880fdec998a9b;hp=adf93fa64d35b8c645d7e3c72928f8585fdf2e03;hpb=21c2c8445fd1d0c6ed630a2ecb259ddd9712c750;p=sbp.git

diff --git a/src/edu/berkeley/sbp/Sequence.java b/src/edu/berkeley/sbp/Sequence.java
index adf93fa..ac34264 100644
--- a/src/edu/berkeley/sbp/Sequence.java
+++ b/src/edu/berkeley/sbp/Sequence.java
@@ -87,7 +87,15 @@ public abstract class Sequence extends Element implements Iterable<Element> {
     // Position //////////////////////////////////////////////////////////////////////////////
 
     /** the imaginary position before or after an element of a sequence; corresponds to an "LR item" */
-    public class Position {
+    public class Position implements IntegerMappable {
+
+        private Forest zero = null;
+        public Forest zero() {
+            if (zero != null) return zero;
+            if (pos > 0) throw new Error();
+            return zero = rewrite(null);
+        }
+
 
                 final int      pos;
         private final Position next;
@@ -100,11 +108,6 @@ public abstract class Sequence extends Element implements Iterable<Element> {
         }
 
         boolean isFirst() { return pos==0; }
-        boolean isRightNullable(Walk.Cache cache) {
-            if (isLast()) return true;
-            if (!element().possiblyEpsilon(cache)) return false;
-            return next().isRightNullable(cache);
-        }
 
         /** the element immediately after this Position, or null if this is the last Position */
         public Element  element() { return pos>=elements.length ? null : elements[pos]; }
@@ -118,7 +121,7 @@ public abstract class Sequence extends Element implements Iterable<Element> {
         /** true iff this Position is the last one in the sequence */
         public boolean isLast() { return next()==null; }
 
-        // Reduction /////////////////////////////////////////////////////////////////////////////////
+        // Position /////////////////////////////////////////////////////////////////////////////////
 
         final <T> Forest<T> rewrite(Token.Location loc) {
             if (this==firstp()) return epsilonForm();
@@ -142,14 +145,16 @@ public abstract class Sequence extends Element implements Iterable<Element> {
             for(Position p = Sequence.this.firstp(); p != null; p = p.next()) {
                 ret.append(' ');
                 if (p==this) ret.append(" | ");
-                if (p.element()!=null) ret.append(p.element().possiblyEpsilon(null) ? "["+p.element()+"]" : p.element());
+                if (p.element()!=null) ret.append(p.element());
                 else                   ret.append(' ');
             }
             ret.append("}>");
             return ret.toString();
         }
+        private final int idx = master_position_idx++;
+        public int toInt() { return idx; }
     }
-
+    private static int master_position_idx = 0;
 
     // toString //////////////////////////////////////////////////////////////////////////////