X-Git-Url: http://git.megacz.com/?p=sbp.git;a=blobdiff_plain;f=src%2Fedu%2Fberkeley%2Fsbp%2FParser.java;h=6bf274d30ecb6bde3135d9fce9061321c9a63d47;hp=ab0688966495d0ee149c14e02306e2eee7c5ce38;hb=96a2822a729e563a64173f22dc184bc972a200ef;hpb=6b53048f4413f3c618acc3581d0b4f60a236a9bc;ds=sidebyside

diff --git a/src/edu/berkeley/sbp/Parser.java b/src/edu/berkeley/sbp/Parser.java
index ab06889..6bf274d 100644
--- a/src/edu/berkeley/sbp/Parser.java
+++ b/src/edu/berkeley/sbp/Parser.java
@@ -9,7 +9,7 @@ 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;
 
@@ -24,16 +24,15 @@ public class Parser<T extends Token, R> {
         if (p.element() != null) reachable(p.element(), h);
     }
 
-    //public Parser(          Topology top) { this(new Table(   top)); }
-    //public Parser(String s, Topology top) { this(new Table(s, top)); }
-
     /**
      *  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(); }
@@ -46,7 +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;
@@ -80,12 +80,13 @@ 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();