"Human-readable" ANTLR-generated code?

Question

I've been learning ANTLR for a few days now. My goal in learning it was that I would be able to generate parsers and lexers, and then personally hand-translate them from Java into my target language (neither C/C++/Java/C#/Python, no tool has support for it). I chose ANTLR because from its About page: ANTLR is widely used because it's easy to understand, powerful, flexible, generates human-readable output[...]

In learning this tool, I decided to start with a simple lexer for a simple grammar: JSON. However, once I generated the .java file for this lexer using ANTLR4 I was caught widely off-guard. I got a huge mess of far-from-human-readable serialized code, followed by:

    public static final ATN _ATN =
    ATNSimulator.deserialize(_serializedATN.toCharArray());
static {
    _decisionToDFA = new DFA[_ATN.getNumberOfDecisions()];
}

A few Google searches were unable to provide me a way to disable this behavior.

Is there a way to disable this behavior and produce human-readable code, or am I going to have to hand-write my lexers and parsers for this target programming language?

Sam Harwell Sam Harwell · Accepted Answer · 2013-05-03T16:28:30

ANTLR 4 uses a new algorithm for prediction. Terence Parr is currently working on a tech report describing the algorithm in detail. The human-readable output refers to the generated parsers.

ANTLR 4 lexers use a DFA recognizer for a massive speed and memory usage improvement over previous releases of ANTLR. For parsers, the _ATN field is a data structure used within calls to adaptivePredict (you'll notice lines in the generated code calling that method).

You won't be able to manually translate the generated Java code of an ANTLR 4 lexer to another programming language. You might be able to manually translate the code of a generated parser provided the grammar is strictly LL(1) (i.e. the generated code does not contain any calls to adaptivePredict). However, you will lose the error recovery ability that draws from information encoded in the serialized ATN.

"Human-readable" ANTLR-generated code?

1 Answers