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Developing Applications With Objective Caml
The Book The book itself is quite comprehensive, clocking in at over 700 pages and covering material ranging from an introduction to the language to concurrent and distributed programming. To organize all of this material, the book is broken into four main sections that build upon each other. Each section has a set of chapters that present some related concepts, followed by an "Applications" chapter that uses those concepts to create a few small applications such as a minesweeper game, a graphical interface library, a couple of different two-player games, a distributed robot simulation, and a basic HTTP servlet. These four sections are as follows:
I. Language Core
This section serves primarily as an introduction to the OCaml language, with chapters on the functional core and imperative aspects of the language, a chapter on the differences between the two styles that shows how the two can be melded, and a chapter on the OCaml Graphics module. The introduction to OCaml is complete enough that anyone with a background in programming should be able to achieve a good understanding of the basics of the language. Especially when combined with other freely available resources, like Jason Hickey's Introduction to Objective Caml , and Richard Jones' Learning OCaml for C, C++, Perl and Java programmers, one should be able to obtain a strong OCaml foundation to use while reading the rest of this book.
II. Development Tools
The second section covers, as the title states, the OCaml development tools. The chapters in this section provide information on the OCaml compilers, interpreter, and interactive toplevel environment; some of the libraries included with the standard distribution; OCaml's garbage collection mechanism; Ocaml's debugging and profiling tools; OCaml's versions of lex and yacc; and interfacing OCaml with C. This is perhaps the most valuable section of the book, as it provides good coverage of some important topics that are covered a bit too briefly in the OCaml manual.
III. Application Structure
This section covers the OCaml Module system, and its interface and functor (parameterized module) facilities. Also included in this section is a well written chapter on object oriented programming in OCaml, and a chapter comparing the two models of program organization, offering a brief look at how the two systems can be combined to reap the benefits of both.
IV. Concurrency and Distribution
The final section covers the topics that many folks might consider to be the "real world" programming topics: File I/O, process management and communication, concurrent programming using threads, and distributed programming. The coverage in this section is, again, well done, but perhaps a bit light, and it would have been nice to see more time spent on this subject matter. However, the book is already quite hefty, and the services provided by OCaml's Unix module should look familiar enough to most programmers that the material that is presented should be sufficient to get a competent programmer up and running.
The Upshot For the most part, Developing Applications With Objective Caml does a very good job at presenting the OCaml language in more of a "practical" light than other books on languages in the ML family (and functional languages in general). And while the applications that are constructed throughout this book aren't anything particularly great or interesting in and of themselves (a simple BASIC interpreter, a rudimentary database, a client-server toolbox, etc.), they aren't the primary purpose of the book. What the applications are used for is to illustrate how the concepts presented earlier in the book are used in within the framework of an application, and not just as isolated examples. This is especially important, as most people who might read the book will be unfamiliar not just with Objective Caml, but with the entire functional programming paradigm. Repeated exposure to working OCaml code helps to familiarize the reader with functional programming and OCaml idioms while reinforcing the book's material.
There are, of course, some problems with the book. For one thing, Developing Applications is nearly five years old, half a lifetime when dealing with most computer related topics. This issue is first brought to light in the introduction where it's mentioned that chapter one tells how to install version 2.04 (OCaml is currently at version 3.08), and then in chapter one, when the reader is warned that, "Objective Caml only works under recent versions of Windows : Windows 95, 98 and NT." Fortunately, the information presented about the language remains valid (and Appendix B presents some of the features added to the language by version 3.04, the release that was current at the time of the translation). There are also a few spots where the code in the book contains minor errors, but both of these issues can easily be overcome with the help of the resources listed earlier in this review, or with the help of the OCaml community. Other minor issues crop up as a result of the translation, with the occasional odd sounding phrase popping up in the text and examples. These problems are, however, few and far between and do little to detract from the material or the presentation. And so this book still remains one of the best resources for learning Objective Caml. I used it when I was learning the language, and I still turn to it from time to time as a useful resource.
Will the book turn you into an OCaml guru, or teach you all sorts of advanced type system trickery? No, of course not. But it can teach you enough about the language to start you writing real apps in it. And it will allow you to add a fast, flexible, and powerful language to your toolbox.
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Well, that may have been true five or ten years ago, but have you checked the Caml humps http://caml.inria.fr/humps/ recently ?
For GUI you have Tk, GTK, GTK2 ; some people have written interfaces to the Win32 API. Concerning data structures, the standard library has lots (lists, hashtables, queues, sets, maps), and if that's not enough, you name it, you have it (from splay trees to bitvectors), and not only esoteric data structures available only in functional languages. With Bigarray you can MMap huge arrays of whatever you want (bytes, floats). With the built-in lazy streams you can easily hack a LL parser, and if that's not enough you can run ocamlyacc. There are interfaces for Postgresql, mysql. Unix support is very complete (and portable). There is a good crypto library. For number-crunching you have the built-in number library, GMP bindings or numerix. Interfacing to C is excellent. I mean, come on, Perl and Java have, today, more in their libraries, but you really can't call Ocaml's library support "pathetic". Ocaml can and is really used for real apps (Coq, MLDonkey, etc.) with real GUIs. You can't say the same for Scheme. Plus, Ocaml compiles to machine code on i386, PowerPC and a few other architectures, and that runs damn fast even if you don't spend the afternoon optimizing your code.
I don't know; I've always been able to find libraries that I needed for Haskell; there are quite a few listed on the Haskell libraries page. It seemed to me, when I was evaluating OCaml, that a lack of libraries bindings or bindings to other language's libraries was not a problem. They've got quite a decent database of extensions at The Camel Humps
I'm mainly a Java and Ruby developer, though, so I may not have stressed tested the availability of Haskell libraries. Java doesn't use libraries; if somebody writes a third-party library for it, Sun re-implements it, poorly, and bundles it with the VM, which effectively kills the original, and often superior, library. And Ruby... well, you just create whatever bindings you need, dynamically, with 'dl'.
--- SER
One solution that many of these languages are now taking is to target either the .NET framework or the JVM. For example, F# and SML.NET are two different projects from Microsoft Research aimed at producing ML-like compilers targeted at .NET. The Bigloo Scheme compiler now has an experimental .NET backend in addition to native code and JVM backends. There are also some Haskell compilers targetting the .NET now. If you look around, quite a few functional languages are beginning to support some combination of .NET and the JVM.
.NET or JVM gets them off the ground right away.
.NET is a bit easier, though there are still some quirks. Many of those are known at this point, however, and there are even some libraries even to help work around them (e.g. the ILX SDK developed for F#.) I also think I recall something about the next update to MSIL addressing many of those quirks to simplify the development of functional language compilers.
For many languages, this solves exactly the problem that you describe. The new language instantly gets the benefit of large, useful and well tested library. The language developers can focus on the design of their language and leave the hassle of building and maintaining the supporting run-time and library to someone else. Eventually they can add a more native-feeling system library layer over it, but targeting the
There's a few quirks involved in shoehorning functional languages this way. As I recall, the JVM is a bit more difficult to compile functional languages to since it is really intended to run Java.
I've also written an OCaml tutorial for people coming from 'conventional' languages like C, Perl and Java.
Rich.
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