[antlr-interest] NullPointerException in TreeRewriter

Anders Hessellund anders.hessellund at gmail.com
Wed Mar 25 12:10:06 PDT 2009


Hi,

I just updated to 3.1.3 to try TreeRewriter but I get a strange
NullPointerException?

This is my tree grammar:

tree grammar Reducer;
> options {
>     tokenVocab=Expression;
>     ASTLabelType=CommonTree;
>     output=AST;
>     filter=true;
> }
> topdown
>     :    ^(MULT a=. b=INT {$b.int==0}?) -> $b // x*0 -> 0
>     ;
> bottomup
>     :    ^(DIV a=. b=INT {$b.int==0}?) -> $b // x*0 -> 0
>     ;
>

I use the following code to invoke the Reducer. (tree is the CommonTree
object from my parse)

    final CommonTreeNodeStream nodes = new CommonTreeNodeStream(tree);
>     final McAntlrExpressionReducer reducer = new
> McAntlrExpressionReducer(nodes,env);
>     tree = (CommonTree) reducer.downup(tree);


When I run this on the following expression "3*0" I get the following error:

20:09:08.226 [main] DEBUG expression.Expression - parsing '3*0' results in
this AST: (* 3 0)
20:09:08.226 [main] DEBUG expression.Expression - before reduction: (* 3 0)
java.lang.NullPointerException
    at
org.antlr.runtime.tree.CommonTreeNodeStream.<init>(CommonTreeNodeStream.java:67)
    at org.antlr.runtime.tree.TreeRewriter.applyOnce(TreeRewriter.java:56)
    at org.antlr.runtime.tree.TreeRewriter$1.pre(TreeRewriter.java:86)
    at org.antlr.runtime.tree.TreeVisitor.visit(TreeVisitor.java:28)
    at org.antlr.runtime.tree.TreeRewriter.downup(TreeRewriter.java:89)
    at
com.maconomy.expression.McAbstractExpression.reduce(McAbstractExpression.java:58)
    at com.maconomy.expression.test.MtReducerTest.add(MtReducerTest.java:27)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at
org.junit.internal.runners.TestMethodRunner.executeMethodBody(TestMethodRunner.java:99)
    at
org.junit.internal.runners.TestMethodRunner.runUnprotected(TestMethodRunner.java:81)
    at
org.junit.internal.runners.BeforeAndAfterRunner.runProtected(BeforeAndAfterRunner.java:34)
    at
org.junit.internal.runners.TestMethodRunner.runMethod(TestMethodRunner.java:75)
    at
org.junit.internal.runners.TestMethodRunner.run(TestMethodRunner.java:45)
    at
org.junit.internal.runners.TestClassMethodsRunner.invokeTestMethod(TestClassMethodsRunner.java:66)
    at
org.junit.internal.runners.TestClassMethodsRunner.run(TestClassMethodsRunner.java:35)
    at
org.junit.internal.runners.TestClassRunner$1.runUnprotected(TestClassRunner.java:42)
    at
org.junit.internal.runners.BeforeAndAfterRunner.runProtected(BeforeAndAfterRunner.java:34)
    at
org.junit.internal.runners.TestClassRunner.run(TestClassRunner.java:52)
    at
org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:45)
    at
org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
    at
org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:460)
    at
org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:673)
    at
org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:386)
    at
org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:196)

Can anyone help me with this?

-- Anders
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://www.antlr.org/pipermail/antlr-interest/attachments/20090325/18a6e84b/attachment.html 


More information about the antlr-interest mailing list