refactoring to eliminate Token.result()

[sbp.git] / src / edu / berkeley / sbp / Parser.java

diff --git a/src/edu/berkeley/sbp/Parser.java b/src/edu/berkeley/sbp/Parser.java
index 046e725..6bf274d 100644 (file)
--- a/src/edu/berkeley/sbp/Parser.java
+++ b/src/edu/berkeley/sbp/Parser.java
@@ -9,20 +9,30 @@ import java.util.*;
 import java.lang.reflect.*;
 
 /** a parser which translates streams of Tokens of type T into a Forest<R> */
-public class Parser<T extends Token, R> {
+public abstract class Parser<T extends Token, R> {
 
     private final Table pt;
 
-    //public Parser(          Topology top) { this(new Table(   top)); }
-    //public Parser(String s, Topology top) { this(new Table(s, top)); }
+    private static void reachable(Element e, HashSet<Position> h) {
+        if (e instanceof Atom) return;
+        for(Sequence s : ((Union)e))
+            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);
+    }
 
     /**
      *  create a parser to parse the grammar with start symbol <tt>u</tt>
-     *  @param top a "sample" Topology<T> that can be cloned (FIXME, demanding this is lame)
      */
-    public Parser(Union u,  Topology<T> top) { this(new Table(u, top)); }
+    protected Parser(Union u)  { this.pt = new Table(u, top()); }
+    protected Parser(Table pt) { this.pt = pt; }
+
+    public abstract Forest<R> shiftedToken(T t);
+    public abstract Topology<T> top();
 
-    Parser(Table pt)               { this.pt = pt; }
 
     /** parse <tt>input</tt> for a exactly one unique result, throwing <tt>Ambiguous</tt> if not unique or <tt>Failed</tt> if none */
     public Tree<R> parse1(Token.Stream<T> input) throws IOException, Failed, Ambiguous { return parse(input).expand1(); }
@@ -35,7 +45,8 @@ public class Parser<T extends Token, R> {
         for(;;) {
             GSS.Phase next = gss.new Phase(current, input.next());
             current.reduce();
-            current.shift(next);
+            Forest forest = current.token==null ? null : shiftedToken((T)current.token);
+            current.shift(next, forest);
             if (current.isDone()) return (Forest<R>)current.finalResult;
             current.checkFailure();
             current = next;
@@ -69,18 +80,19 @@ public class Parser<T extends Token, R> {
 
     // Table //////////////////////////////////////////////////////////////////////////////
 
+    static class Top extends Union { public Top() { super("0"); } }
+
     /** an SLR(1) parse table which may contain conflicts */
     static class Table {
 
         private final Union start0 = new Top();
         private final Sequence start0seq;
-        static class Top extends Union { public Top() { super("0"); } }
         
         public final Walk.Cache cache = new Walk.Cache();
         
         public HashSet<Position> closure()       {
             HashSet<Position> hp = new HashSet<Position>();
-            start0.reachable(hp);
+            reachable(start0, hp);
             return hp;
         }
         public Position firstPosition()          { return start0seq.firstp(); }
@@ -144,7 +156,7 @@ public class Parser<T extends Token, R> {
                     // FIXME: how does right-nullability interact with follow restrictions?
                     // all right-nullable rules get a reduction [Johnstone 2000]
                     if (p.isRightNullable(cache)) {
-                        Walk.Follow wf = new Walk.Follow(top.fresh(), p.owner(), all_elements, cache);
+                        Walk.Follow wf = new Walk.Follow(top.empty(), p.owner(), all_elements, cache);
                         Reduction red = new Reduction(p);
                         state.reductions.put(wf.walk(p.owner()), red);
                         if (wf.includesEof()) state.eofReductions.add(red, true);
@@ -153,7 +165,7 @@ public class Parser<T extends Token, R> {
                     // 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()).top()));
+                        state.shifts.addAll(state.gotoSetTerminals.subset(((Atom)p.element())));
                 }
         }
 
@@ -223,8 +235,8 @@ public class Parser<T extends Token, R> {
                     if (position.isLast() || !(position.element() instanceof Atom)) continue;
                     Atom a = (Atom)position.element();
                     HashSet<Position> hp = new HashSet<Position>();
-                    position.next().reachable(hp);
-                    bag0.addAll(a.top(), /*clo.walk()*/hp);
+                    reachable(position.next(), hp);
+                    bag0.addAll(a, /*clo.walk()*/hp);
                 }
 
                 // Step 1b: for each _minimal, contiguous_ set of characters having an identical next-position
@@ -262,7 +274,7 @@ public class Parser<T extends Token, R> {
                     if (ys != null) {
                         for(Element y : ys) {
                             HashSet<Position> hp = new HashSet<Position>();
-                            p.next().reachable(hp);
+                            reachable(p.next(), hp);
                             move.addAll(y, hp);
                         }
                     }