[antlr-interest] NullPointerException in TreeRewriter
Anders Hessellund
anders.hessellund at gmail.com
Thu Mar 26 01:39:10 PDT 2009
Hi,
You're right I did not set a tree adaptor. I was actually trying the example
from the wiki but there is no mention of a tree adaptor there?
http://www.antlr.org/wiki/display/~admin/2008/11/30/Example+tree+rewriting+with+patterns
Any ideas?
-- Anders
On Wed, Mar 25, 2009 at 9:20 PM, Terence Parr <parrt at cs.usfca.edu> wrote:
> weird. oh, if you look at code it thinks the adaptor is null...maybe you
> set it incorrectly or don't have one on the nodestream or reducer?
> Ter
>
> On Mar 25, 2009, at 12:10 PM, Anders Hessellund wrote:
>
> 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
>>
>> List: http://www.antlr.org/mailman/listinfo/antlr-interest
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>>
>
>
--
Anders Hessellund
www.itu.dk/people/hessellund/
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