alexeygrigorev/rseq

Rseq is a Java library that lets you search through lists of objects the way you'd search through text with a regular expression. Instead of being limited to scanning strings character by character, you can define a pattern and find matches in any sequence of Java objects. This is useful when you have ordered data and need to spot specific combinations or structures within it. At a high level, you build a pattern by chaining together matching rules. For example, you can tell the library to look for a specific item, optionally skip a word like "the" or "a," and then capture whatever comes next so you can use it later. Once you define this sequence of rules, the library scans your list and identifies where those conditions are met. It also handles common Java data structures directly and provides ways to save or capture portions of the match for later use. A practical use case would be processing a list of words or tokens from a sentence. If you want to automatically extract definitions, you could write a pattern that looks for a word, then the word "is," then an optional "the" or "a," and finally the definition itself. Instead of writing custom loops and logic to parse the sentence, the library handles the matching for you. Beyond simple matching, the library supports variables, grouping, optional elements, and a version of the Kleene star, which allows for repeating elements. The README doesn't go into detail on how to write these custom matchers, but it points to a separate tutorial for those looking to explore further.