ANTRL4: Can't get Python ANTLR to generate a graphic of the parse tree

Question

I have a simple HelloWorld.g4 grammar (see it at the bottom). I am able to successfully generate the .py files using this:

set CLAS         


        

Answer 1

Ran into this today as well: The problem is that the testrig expects the generated java source code. But since you're on Python you don't have it unless you explicitly run antlr4 twice: Once for target language Python2 (or 3) and once for -Dlanguage=java.

See this answer which suggests to run the language=java target first. Then the comment on the question itself to compile the java files.

And for completeness and before it's forgotten: Ensure your $CLASSPATH env variable is set up so that it includes both a dot '.' and the path to the antlr*.jar file. For example on unix:

export CLASSPATH=".:/<Mydirectory>/antlr-4.2.2-complete.jar:$CLASSPATH"

Here's a step by step of what I guess you have to do once the $CLASSPATH is set correctly:

Compile for java:

> antlr4 -Dlanguage=java HelloWorld.g4
# or:  java org.antlr.v4.Tool -Dlanguage=java HelloWorld.g4

Note that I have the options { language=Python3 } in my grammar file and the -D override did not work as expected. So I removed the option block and specify the language target on the command line now.

Then compile the *.java files into *.class files:

> javac -g *.java

Then run the testrig:

> grun HelloWorld message
# or: java org.antlr.v4.gui.TestRig HelloWorld message -gui < input.txt