TokenIndex

TokenIndex is a term used in computing to refer to the position of a token within a sequence produced by tokenization. In text processing, a token is a unit such as a word, punctuation mark, or subword. TokenIndex identifies where that token sits in the ordered stream, often starting at zero or one.

In lexical analysis and parsing, tokenIndex helps track the current token during processing. A tokenizer or lexer emits tokens and advances tokenIndex as it progresses. Parsers may rely on tokenIndex to implement lookahead, error reporting, and backtracking by referencing the token at a specific position in the token stream. Because tokens are often stored in an array or linked sequence, tokenIndex serves as an efficient pointer into that structure.

Data structures commonly associated with tokenIndex include a Token object or record with fields such as type, value, line, column, and index or start/end character offsets. tokenIndex may be the position of the token within the list of all tokens, while separate offset fields map tokens back to their location in the original source text. The exact naming and semantics can vary by language and framework, but the concept remains a simple, ordinal position.

Applications extend beyond compilers and interpreters to natural language processing and information retrieval. In NLP, tokenIndex helps align tokens with features, embeddings, or annotation schemes. In search engines, a token stream and its indices can support term-attribution and query matching. Overall, tokenIndex is a foundational concept for organizing and referencing tokenized data.