This is a short post to document an issue we ran into at work so it will show up in search results for people who have this problem in the future.
I recently finished a basic XLSX reader for OCaml and I thought it would be a good time to summarize what's necessary to make a library like this, since the documentation is complicated and sometimes hard to find.
If you're planning to read XLSX files, you probably want to …
From a non-theoretical engineer perspective, a monad is a kind of container that you can apply functions to to get a new monad. In particular, you need a way to put something into your monad and a way to apply changes to it. These are called return and bind. There is also a third operation, map, which is a combination of the two. Note that monads are allowed to be empty, which will make bind and map not do anything; and they can also contain more than one thing (in which case bind and map will call the function you give them more than once and merge the results).
I've been working on an OCaml library to read XLSX files, and something I thought was odd is that all strings in an Excel workbook are listed in a "shared strings" file and then referenced by index. This seemed strange to me, since I would expect the compression algorithm to do this kind of work for you, but thinking about it made me better understand why that's necessary, and also what the advantages and disadvantages of the ZIP and tar + compression formats are.
One of the hardest parts of learning OCaml is figuring out what the infix operators do, since they're just a string of symbols and you can't find them with a Google search. This is my attempt to make a cheatsheet for whenever you're wondering what a random series of symbols means.