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
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
Raphael wrote: Does antlr build the AST for us automatically by option{output=AST;}? Or do I have to make the tree myself? If it does, then how to spit out the nodes on that AST? No, the parser does not know what you want as root and as leaves for each parser rule, so you’ll have … 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
Note: this answer is for ANTLR3! If you’re looking for an ANTLR4 example, then this Q&A demonstrates how to create a simple expression parser, and evaluator using ANTLR4. You first create a grammar. Below is a small grammar that you can use to evaluate expressions that are built using the 4 basic math operators: +, … 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