|go ahead... be a heretic|
Nice, looks interesting and eminently useful. Of course the "any time the user suspects" part is a bit weak.
it's impossible to find the Nth occurrence of some phrase or word in a book without opening the book and counting your way through it.
I would like to note that after practice I became able to consistently open a book to the correct page in the case of a thick Japanese character dictionary (Nelson's) back in school. I think this may be like a lookup table that matches thickness of pages before one's thumb to a list of >100 chapters. At least it always worked for the most important chapter.
So if you know where a change had been made in a file, you could in fact jump to a prestudied location before that point, which you know has X occurrences of a pattern before it, and then count N-X occurrences starting from there instead. Metadata describing the various prestudied points (or results of prerun pattern matches) could be saved in a memo at the head of the index file.
You could also save a series of checksums per chapter (if not per line) and this could help determine where a change was made, though maybe Diff could do something similar. This would let you enjoy the benefits of a flat file, i.e. do regex pattern matching or tie the file to some module's object model like Config, while also enjoying some of the structure given by a record-based object store.
Personally I would probably rather have an index that operated based on keywords or patterns than using a recno. If the text file has a list of paragraphs, I could save a few words describing each paragraph in the index and then later jump to the Nth article matching a given keyword or above a certain score. Or perhaps I have a list of events in a calendar, and each would have an event type or event owner associated with it. In this case maybe I would like to have multiple lines per record, in other words the delimiter would not be "\n". Maybe I'd like a (not necessarily unique) date-based key, or a certain format serial number. These are just ideas.
I am trying to think of when I would want to use your new module, and I keep thinking of extracting descriptive words from text as in NLP (natural language processing) and saving them with each paragraph or sentence. Regardless of whether this is a single flat file or not, it would be useful, and a tool to navigate the precompiled index with pointers into the data would seem useful. Perhaps a callback or plugins for index creation would be useful.
At the moment I am thinking of indexing books, which make nice flat files. I wrote a little program that lets me read books from my server on my cell phone when on the train (turns out that's not cheap but..) anyway I read 10KB per page (max that fits in RAM and enough to reach the next station). It would be nice if I had an index built so as to allow me to make one page end at the end of a sentence, within the 10K limit. It is so much of a pain that currently I even split words across pages. A recno could be used as a bookmark, if the recno is created based on a page length and a "try not to break sentences across pages" heuristic. So to make a long story short, it would be interesting if your module would support creation of indices based on pages of a length decided somewhat intelligently. Would that be possible with your module? Keep up the good work!