[antlr-interest] NullPointerException in TreeRewriter

Anders Hessellund anders.hessellund at gmail.com
Thu Mar 26 06:57:33 PDT 2009


Hi,

I found the cause. When you call the 1-arg constructor in the TreeRewriter
class, it does not set the TreeAdaptor:

    public TreeRewriter(TreeNodeStream input) {
>         super(input);
>     }
>     public TreeRewriter(TreeNodeStream input, RecognizerSharedState state)
> {
>         super(input, state);
>         originalAdaptor = input.getTreeAdaptor();
>         originalTokenStream = input.getTokenStream();
>     }
>

Shouldn't the 1-arg constructor rather be?

    public TreeRewriter(TreeNodeStream input) {
>         super(input,new RecognizerSharedState());
>     }
>     public TreeRewriter(TreeNodeStream input, RecognizerSharedState state)
> {
>         super(input, state);
>         originalAdaptor = input.getTreeAdaptor();
>         originalTokenStream = input.getTokenStream();
>     }
>

Cheers,

Anders

On Thu, Mar 26, 2009 at 9:39 AM, Anders Hessellund <
anders.hessellund at gmail.com> wrote:

> 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<http://www.antlr.org/wiki/display/%7Eadmin/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
>>> Unsubscribe:
>>> http://www.antlr.org/mailman/options/antlr-interest/your-email-address
>>>
>>
>>
>
>
> --
> Anders Hessellund
> www.itu.dk/people/hessellund/
>



-- 
Anders Hessellund
www.itu.dk/people/hessellund/
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