![]() ![]() It does that by turning off the actions while backtracking. Unlike most backtracking parsers, ANTLR v3 supports arbitrary actions, even those that cannot be undone. this does bring up the whole issue again in Java of generating static arrays (see Implementing parsers and state machines in Java). The bytecodes even for large grammar shouldn't be more than a few k or 10s of k bytes. Even if you don't plan on interpreting the grammar, I think I will generate the bytecodes anyway for the recovery stuff I describe below. The bytecodes are like a serialized version of the ATN. If you don't mind a code generation phase but don't want a huge output file typical of recursive descent parsers, we could also generate the bytecode for a PDA into a Java file. ![]() Then, we can simply run an interpreter over the ATN. We can short-circuit the ANTLR tool at the point it's created an internal ATN but before code generation. It would be nice to have a good interpreter that could parse input described by a grammar without having to deal with code generation. Sometimes you need to parse some data but going through the whole ANTLR code generation and then compilation process is overkill. ![]() The data structure will effectively be a recursive transition network (RTN) or, if there are predicates and actions, an augmented transition network (ATN). support "code completion / intellisense" type functionality in development environmentsįrom the bytecodes, we can build a data structure in memory that will be more convenient for a lot of purposes.the mechanism for handling lexical constructs that a DFA cannot handle.the backtracking mechanism for parsers and tree parsers.a pure interpreted version of a lexer/parser/tree parser related work: A Text Pattern-Matching Tool based on Parsing Expression Grammars, but I will need to extend for semantic predicates and actions.The interpreter will serve many useful purposes: I'm proposing something a little different for v4: Along with a recursive-descent parser, I'm going to serialize the grammar down to a simple PDA (push-down automaton) represented by the bytecodes of an interpreter (Derived partially from Cox' description of Thompson's 1960s work). Ok, so what does all that title nonsense have to do with ANTLR v4? Well, v4 will use all those things at some point, either in analysis or in the generated code. Get 9,000+ Interview Questions & Answers in an eBook.At long last, I'm back on the ANTLR v4 rebuild after 9 months hiatus to write an academic LL(*) paper with Kathleen Fisher and release StringTemplate v4. ![]() Converting NFA to DFA - Lexical Analysis Study Notes for GATE ![]()
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