There are a couple of alternatives you shouldn’t rule out: JParsec is a parser combinator framework that allows you to construct your parser entirely from code. Scala’s parser combinator framework addresses a similar concern; however, Scala’s syntax makes all of this much more readable. Then there’s also the parser combinator framework done by John Metsker, … Read more
ANTLR provides a header tool which allows you to include package and imports. You include this in your *.g grammar file: @header { package org.xmlcml.cml.converters.antlr; import java.util.HashMap; } And you may need it in the Lexer as well: @lexer::header {package org.xmlcml.cml.converters.antlr;} and in case you need to add some members and code: @members { HashMap<String, … Read more
I believe I understand the problem. The exception is being caught, the issue is confusion over the debugger’s behavior and differences in the debugger settings among each person trying to repro it. In the 3rd case from your repro I believe you are getting the following message: “NoViableAltException was unhandled by user code” and a … Read more
By default, ANTLR 4 generates listeners. But if you give org.antlr.v4.Tool the command line parameter -visitor, ANTLR generates visitor classes for you. These work much like listeners, but give you more control over which (sub) trees are walked/visited. This is particularly useful if you want to exclude certain (sub) trees (like else/if blocks, as in … Read more
Let’s say you want to parse simple expressions consisting of the following tokens: – subtraction (also unary); + addition; * multiplication; / division; (…) grouping (sub) expressions; integer and decimal numbers. An ANTLR grammar could look like this: grammar Expression; options { language=CSharp2; } parse : exp EOF ; exp : addExp ; addExp : … Read more
Ok, let’s build a simple math example. Building an AST is totally overkill for such a task but it’s a nice way to show the principle. I’ll do it in C# but the Java version would be very similar. The grammar First, let’s write a very basic math grammar to work with: grammar Math; compileUnit … Read more
ANTLR 4 For predicates in ANTLR 4, checkout these stackoverflow Q&A’s: Syntax of semantic predicates in Antlr4 Semantic predicates in ANTLR4? ANTLR 3 A semantic predicate is a way to enforce extra (semantic) rules upon grammar actions using plain code. There are 3 types of semantic predicates: validating semantic predicates; gated semantic predicates; disambiguating semantic … Read more
A fragment is somewhat akin to an inline function: It makes the grammar more readable and easier to maintain. A fragment will never be counted as a token, it only serves to simplify a grammar. Consider: NUMBER: DIGITS | OCTAL_DIGITS | HEX_DIGITS; fragment DIGITS: ‘1’..’9′ ‘0’..’9’*; fragment OCTAL_DIGITS: ‘0’ ‘0’..’7’+; fragment HEX_DIGITS: ‘0x’ (‘0’..’9′ | … Read more
Update/warning: This answer may be out of date! One major difference is that ANTLR generates an LL(*) parser, whereas YACC and Bison both generate parsers that are LALR. This is an important distinction for a number of applications, the most obvious being operators: expr ::= expr ‘+’ expr | expr ‘-‘ expr | ‘(‘ expr … Read more
Would the dynamic linq library help here? In particular, I’m thinking as a Where clause. If necessary, put it inside a list/array just to call .Where(string) on it! i.e. var people = new List<Person> { person }; int match = people.Where(filter).Any(); If not, writing a parser (using Expression under the hood) isn’t hugely taxing – … Read more