[mxz3000]

My experience has been similar to yours. The company I work at has very complex business logic written as a custom DSL parsed/executed by a crazy pile of Perl code.

Recently we had requirements to come up with a way of providing on-the-fly validation in a web editor. This was only possible by ditching the old implementation and re-writing the grammar using ANTLR. While the old implementation is unmaintainable and (probably, who knows?) buggy, the ANTLR implementation is trivial to work on, test and add new features to.

If you're working with a limited time budget, which is common when your main job isn't to maintain the language, then parser generators such as ANTLR are a godsend. ANTLR even enables you to generate parsers in different languages depending on where it needs to be executed. Need something to run client-side, in the users browser? Generate a JavaScript parser and you're done. Need it to run in the Java backend? Generate it in Java and call it a day.

While it's true that error handling isn't the best, it's already better than nothing, and, as you say, can probably be improved with a bit of customization.