There's a common programming interview question that asks you to find the single non-duplicated value in a list of duplicated integers. This can be done in O(n) time and O(1) space by XOR'ing the values, and doing so is almost always the wrong answer. A better solution when you can afford to do it is to use a hash table to count occurrences.
Indexing and sorting to find data quickly
To make your data faster to lookup, you can either store it in an order that makes it easier to search, or add one or more indexes. For practical work, you can let your file system do this for you, or use a pre-built database (either relational or not). I'll describe from the lowest-level to highest level so you can understand what I'm suggesting, but my real-world answer is that I would store most kinds of data in a relational database like PostgreSQL and put indexes on any column that I want to do lookups by.
How to write examples for documentation
When you're documenting a project so other people can use it, whether it's a library or web service, one important thing to do is to give people good examples to work with. Not only does this save people time trying to cobble together their first working program, but it's also a good way to show how the library is meant to be used, instead of just what's technically possible.
Easy mistakes when writing OCaml C bindings
I recently spent several days improving the OCaml FreeTDS C bindings for work, and I thought it might be useful to share the problems I ran into and how to solve them.
I tried to order things so the most likely issues are listed first, but if you're trying to debug some C binding crashes, I recommend just reading the whole thing.
This post will assume you're already familiar with the official documentation.
How to use Core.Command.Param
Core.Command (and the closely-related Async.Command) is an OCaml library for creating command line programs with nice interfaces (including help text and argument parsing). This article is an overview of Command.Param, the newer interface for defining your command's arguments.