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Web programming is one of the best ways for a language to gain visibility. Ever since the web gained widespread popularity, developing for web targets has been important for a wide variety of programmers.

Shoutcast is a product from Nullsoft (which is also the creator of the WinAMP MP3 player for Windows) to enable audio broadcasting over a network. Nullsoft’s Shoutcast server enables clients to stream MP3 data from one client to a server, which is the server that clients connect to in order to listen to that data stream. It is, in effect, a multiplexer of audio streams. Shoutcast was one of the first applications of its kind to become popular. Although streaming network audio predates Shoutcast, it was Nullsoft’s product that had the power and flexibility that enabled it to take off.

As you are reading this, you are performing multiple tasks simultaneously. You are thinking about the words on the page, moving your eyes, hearing sounds in your environment, interpreting these sounds, and more. This ability to perform concurrent actions makes things like walking, talking, and pretty much everything else a living being does possible. Most computer programs, however, do not have the capability to perform concurrent actions.

This chapter introduces a concurrent web crawler written in OCaml, which traverses a web server and finds all the local href links. It then outputs information about which pages link together. A web crawler is different from a web browser in that the web crawler is automated. Both are web (or HTTP) clients and are quite similar, but this automation versus interactivity is the important distinction.

No language is an island. There are situations in which a programmer wants to interface code with existing code, or system calls, or a new library that is not written in OCaml. Sometimes this can be accomplished using sockets or some other Remote Procedure Call (RPC) mechanism. Sometimes, though, she will need to interface her OCaml code with foreign functions.

The OCaml standard library is big, but it still could be more complete. Two areas in which it is lacking include time functions and logging. If you are used to a programming language (such as Java or Python) that has an absolutely huge standard library that includes everything you could ever want in the world, you might be disappointed by OCaml’s standard library.

All data is not text. Binary data is used in all kinds of applications. Often, accessing binary data is faster than text data, and it is space-efficient, too. Until now we have not talked about what you need to do differently to process binary data in OCaml.

Having a programming language is not the only thing you need to actually do development in that language. You also need tools that make the process of developing and debugging code easier.

Camlp4, which provides a very interesting and powerful way to extend and change the OCaml language, enables the easy definition of domain-specific languages (DSLs) based on OCaml. The name Camlp4 refers to the fact that it is a preprocessor and pretty printer (four Ps) for OCaml.

You have now arrived at the last chapter of this book. Although this book does not cover all aspects of OCaml programming, I have tried to present information that can help you become an OCaml programmer if you are not one yet—or a better OCaml programmer if you are.