Erlang Now!

I don’t know whether Monty Python ever wrote a gag on programming languages, but if they did, this Erlang video must be it. The funniest thing is that it is pretty serious, and does a great job showing one of my most cherished abilities when using dynamic languages, namely, adding new functionality to a running system on the fly. As for the Monty Python bit, well, you have to see the to know what i mean: i kept laughing out loud during most of its twelve minutes (those Ericsson engineers seem to be taken from The Larch, but then maybe it’s just my sense of humor).

Update: Mike, one of the engineers in the film, has been kind enough to post a comment about the experience, which I’m reproducing here for your convenience:

We gave a well received “demo” in 1990, conjunction with ISS90, a big telecoms conference in Stockholm. We made this movie to record the demo. We actually used a professional company to do the filming, but I won’t mention their names as they would probably sue me for libel.

The worse of it all, is that we were deadly serious at the time. The Monty Python aspect must be due to our backgrounds. Of the people involved, Joe is English, Robert is Swedish – but brought up in Australia, Bjarne is also Swedish but spend some formative years in Scotland and I’m half Welsh half Scottish with some Irish thrown in somewhere.

In 1990, when we made the movie, the very idea of using anything other than C, Plex, assembly language etc to design embedded concurrent systems was heresy, we expected to take the world by storm. It seems that the cheap communication and multi core processors are giving Erlang a boost 16 years later. Well at least in the intervening time we have tested the hell out of Erlang and its implementations!


PS. If you look carefully at the film, you can see that Erlang at that time had a Prolog like syntax.

PPS. I can’t watch the movie without laughing (at) myself

While we’re at it, let me mention that i like many a thing of Erlang. It’s a curious mix of good stuff: a simple syntax and kind of minimalist flavor that reminds of Scheme, pattern matching and functional variables like Haskell’s, and what amounts to a programming paradigm of its own based on mailboxes and processes (which, as you surely know, are amazingly cheap). Also worth mentioning is Erlang’s error handling philosophy, which is, at first sight, a bit startling (i’m not still sure if it makes perfect sense, but after playing with the language a bit, it looks like it does–this is an interesting post on those matters). Definitely worth a look: see for instance Joe Armstrong‘s thesis, or, if you have some bucks to spare, the forthcoming Programming Erlang.

A Scheme bookshelf

It all began while i was using MDK‘s development as an excuse to learn everything i could about programming and programming tools: makefiles, autoconf, automake, localization, texinfo docs, lexers, parsers… and, eventually, extensibility. I kept hearing about an exotic thing by the name of GNU’s Ubiquitous Intelligent Language for Extensions, and, finally, rose to the bait. But my first attempts at writing Scheme felt awkward. Not because of the parens (i liked Scheme syntax from day zero), but basically because i was writing C code using Scheme. Clearly, i needed to read a bit about this new thing and, to that end, i got a copy of The Little Schemer… to no avail: i didn’t get what elephants, food and Socrates had to do with programming; i still felt awkward. (It was not the book’s fault, mind you, but mine. More about this in a bit.)

Then i found the book. Abelson and Sussman’s Structure and Interpretation of Computer Programs changed my life as a programmer. I’m sure you’ve read lots of praise for this book. Totally deserved! SICP is not really about Scheme, but about thinking about programming. Reading it will make you a better programmer in any language. It will expand your mind. It will cure your diseases. It’s really that good. Besides, SICP is freely available in HTML, PDF and texinfo formats, so you really have no excuse. For extra fun, get the accompanying video lectures, by Abelson and Sussman themselves. These lectures are charming: these guys have a passion for what they do, and they transmit it from the very beginning, when Abelson jokingly explains why computer science is neither a science nor about computers.

Concrete AbstractionsThe most cited alternative to SICP is How to Design Programs by Felleisen, Findler, Flatt and Krishnamurthi. Its authors have even published a rationale, The Structure and Interpretation of the Computer Science Curriculum, on why they think SICP is not well suited to teaching programming and how their book tries to fix the problems they’ve observed. I won’t try to argue against such eminent schemers, but, frankly, my feeling is that HtDP is a far, far cry from SICP. HtDP almost made me yawn, and there’s no magic to be seen. If for whatever reason SICP is not your cup of tea, i would recommend Max Hailperin‘s Concrete Abstractions as a far better (as in more fun than HtDP) alternative.

With SICP under my belt, i was ready for The Little Schemer and The Seasoned Schemer(by Daniel P. Friedman and Matthias Felleisen), which i read in a row. You’d be hard pressed to find any programming book similar to the Schemers books. As in my case, the initial reaction may well be of rejection: on a superficial reading they look too queer, even childish, and by any means the kind of book a serious programmer should read, except maybe for fun. But that’s precisely the point: you won’t learn unless it is for fun! If you enter the game proposed by Daniel and Matthias, accepting to participate in their Socratic scheme, you’ll learn a lot with their books. I found easier to put me in the right mood after SICP because it also is imbued of a kind of magic, and also because i was much better equipped to capture the subtleties lurking in every page of the Schemers books. Besides having a great time, one ends up with a sound grasp of higher order functions, recursion (including the Y combinator) and continuations. In fact, it was reading The Seasoned Schemer that something clicked and i really understood continuations.

After all these readings i felt i was starting to have a good grasp of the conceptual underpinnings of Scheme and Lisp, and that it was due time to strengthen the technical details. Or in other words, i wanted to come to grips with the nitty gritty details of Scheme syntax and semantics, including macros (which i knew from some tutorials and readings on Common Lisp). To that end, Dybvig‘s The Scheme Programming Language was the perfect book. Comprehensible, exacting and with an elegant prose, and to the point. But, despite its succinctness, Dybvig does an excellent job in conveying the details of the language and its usage. The book also includes extended usage examples for a good measure. Thus, TSPL works nicely as both a tutorial and a handy reference.

If you already have a good basis on functional programming you can use TSPL as your first Scheme book and skip the previous ones (but you will be skipping lots of fun and, maybe, insight too). And if you happen to read French, an interesting alternative for a speedier learning path is Jacques Chazarain’a Programmer avec Scheme. In the first part of the book, Practical programming with Scheme, Scheme is thoroughly presented, using it in many examples taken from the standard data structures and algorithms curriculum. Taking this practical basis as a starting point, Chazarain proceeds to a comprehensive (almost 400 pages long) discussion of the formal basis of the theory of programming languages: automata, lexers and parsers, propositional calculus, rewriting systems, logic programming, lambda calculus and more. As you can see, the scope of this book is amazing, and it’s well worth learning a little French!

The nice thing about learning a programming language in such a good company is that one learns much more than a single programming language. These books helped me obtain a conceptual basis for thinking about programming and programming languages in abstract terms, applicable to any programming problem. As Sussman colorfully demonstrates in one of the SICP lectures, one feels like beholding the heart of the spirit that lives in the machine. An that spirit, of course, is an interpreter. So i delved into the theory and practice of implementing interpreters guided by another classic: Essentials of Programming Languages by Daniel P. Friedman, Mitchell Wand, and Christopher T. Haynes. This marvelous book delves deep into the art of writing interpreters using Scheme as the implementation language. By way of running example, an interpreter for an ML-like language is developed all along, showing the magic of, among other things, register machines or continuation-passing style. To get a flavor of what this book has to offer, i wholeheartedly recommend reading Friedman’s The Role of the Study of Programming Languages in the Education of a Programmer, an insightful talk on how a theoretical background is useful (and even needed) to any programmer in any language, which Friedman illustrates with practical cases taken from his book.

Sussman the magicianOne of the rites of passage of any self-deserving schemer is writing a metacircular scheme interpreter, that is, a scheme implemented in itself. Having a look at the innards of your language implementation sheds a whole new light on your daily usage of the language. Sussman goes as far as wearing his magician’s hat when he explains the metacircular interpreter in the SICP lectures, and rightly so. But i’ve always felt a bit frustrated by the fact that the implementations one finds in books like SICP, EOPL or, to cite another classical example, PAIP are actually for toy interpreters not covering all the details of real Schemes. And often the left out precisely the most interesting bits! Fortunately, there’s a book that will tell you everything you ever wanted to know about implementing Lisp interpreters and compilers: Lisp in Small Pieces by Christian Queinnec. This is easily the best book about Lisp i have ever read. LiSP shows, without omitting any details, how the family of Lisp languages is implemented (in interpreted and compiled forms). You’ll learn from the inside the difference between Lisp-1 and Lisp-2, how dynamical and lexical scope work, how blocks and continuations are related, how on earth one implements… everything you ever wanted to know about Lisp implementations, and then more. On top of that, Queinnec writing style is engaging and the book is pervaded by a fine sense of humour that made me laugh out loud several times. If you’re serious about Lisp, you must read this book.

Let me close my list of recommendations with the last addition to my Scheme bookshelf, namely, the third schemer installment: The Reasoned Schemer (by Daniel P. Friedman, William E. Byrd, Oleg Kiselyov). Paraphrasing Alan Perlis, the key reason for learning new languages and paradigms is the fact that they, hopefully, change the way you think about programming. Functional languages do a pretty good job at that, but they’re not the only game in town. Declarative programming is definitely another mind blowing experience, which you can enjoy reading The Reasoned Schemer. The book presents, in that peculiar style of its predecessors that i like so much, the basis of logic programming using a Scheme implementation that, in many ways, surpasses standard declarative languages like Prolog. The best of two awesome worlds, and an excellent way to ensure that you keep learning and expanding your programming horizons.

Happy reading!

A couple more exotic input methods

I’ve posted about novel ways to interact with our computers a couple of times before. I know this is a bit off-topic, but, to me at least, programming is also about transforming computers into something useful, and thinking about new ways to interact with them is an excellent way to pursue that goal. After all, all-time favorite languages of mine like Lisp or Smalltalk were born while people were struggling with making computers useful and/or accessible.

I’ve always loved the stories about how our current interaction paradigm was invented by Alan Kay and friends over at Xerox Parc, as recounted in books like Dealers of Lightning or the excellent Tools for Thought; or in papers like Alan Kay’s classic on the history of Smalltalk. The people exploring new ways to interact with computers look to me as the heirs of this tradition. I find also pretty interesting to try and imagine how on earth they’re implementing this new stuff, and would love to hear about the languages and environments they use.

Admittedly, the tricks i’m about to show you have, at first sight, no direct application to our work as programmers, but hey, you know what Hertz thought of his experiments on electromagnetic waves, don’t you?

Yeah, right, i’d better stop talking and show you the cool stuff. The first video (hat tip the Cynical-C Blog) makes true the dream of any physics teacher:

This beauty comes from MIT, but there are already commercial versions (including a free lite version) available from Pintar Media.

I found the second video i want to show you while reading about a ‘Minority Report’ interface created for US military (interesting on its own, by the way). It shows another ‘analogue’ input device called Blue Eye, a kind of universal photocopier (and part of the Visual Interaction Platform):

Blue Eye (WMV video)

OK. Probably more useful to designers than to programmers, but funny anyway, and perhaps a glimpse of the kind of devices we’ll be programming in the not so far future. A challenging prospect, don’t you think so?

Prolog programming contests

From a recent post over at comp.lang.prolog:

We are pleased to announce that the book ‘The First 10 Prolog Programming Contests’ can now be downloaded from here. This book contains the (slightly reworked) questions of the first 10 Prolog programming contests, together with an answer for each question. The solutions can also be downloaded from the above webpage.

Hardcopies of this book are still available, and can be obtained by sending an e-mail to bmd at cs dot kuleuven dot be.

Bart Demoen, Phuong-Lan Nguyen, Tom Schrijvers, Remko Troncon

And, just to whet your appetite, this is a quote from the book’s preface:

Programming is enormously fun. Fun was indeed our main motivation for starting the series of Prolog Programming Contests in 1994. Ask anybody who ever participated in a Prolog Programming Contest: they loved it! There is a thrill in trying to solve five problems in two hours, crammed in a small room filled with ten or more sweaty teams doing the same. And there is a great satisfaction, unmatched by any other daytime scheduled conference event, when the attempt is even partially successful.

A good place to get started in Prolog is the comp.lang.prolog FAQ. Or, for schemers, solving the problems using kanren (or even micro-kanren) sounds like a lot of fun.

A Haskell bookshelf

My favourite scheme implementation is scheme48, which takes its name from its being initially implemented in 48 hours by Richard Kelsey and Jonathan Rees in August 1986. They used Common Lisp on a Symbolics 3600 and Maclisp on a PDP-10.

Now, thanks to Jonathan Tang’s tutorial, you can write yourself a scheme in 48 hours, but using Haskell instead of Lisp. The tutorial is intended as an introduction to Haskell for Schemers (and (brave) programmers in general) wanting to get started in the purest member of the functional family. And it is extremely fun, for instead of following the boring language features overview way, it plunges right on in interesting, hands-on stuff like parser combinators (one of the most beautiful applications of Haskell, if you ask me) or monads. The lessons include exercises, so that you have really no excuse for not learning Haskell once and for all. Believe me, it’s good for your (mental) health.

If you’re totally new to Haskell and find the pace of Jonathan’s tutorial a bit hard to follow, you may start with a tour of the Haskell syntax and the Hitchikers’ guide to Haskell, after making sure, of course, that you have your towel at hand. As for me, well i’ve been planning to learn Haskell for some years now and, since i happen to love books, i have accumulated a little (but selected) Haskell library, together with a sort of learning roadmap that, unfortunately, i have yet to complete. Just in case the above links whetted your appetite and you happen to have more time than i do, here you have my bookworm guide to Haskell enlightenment.

The little Haskeller

There are many introductory Haskell books, but i was (at the time i started learning) keen of those providing also a good basis on functional programming (which was a totally new world for me at the time). Therefore, my first Haskell book, and still a wholehearted recommendation, was Richard Bird and Philip Wadler‘s Introduction to Functional Programming Using Haskell, one of the most elegant books on programming i’ve ever read.

One of the nicest things about writing Haskell code is that it’s the closest one can probably get to writing pure maths while programming. Thus, learning Haskell is an excellent way to learn more about maths and logic. If that sounds to you like doubling the fun (and you’re not yet a math wizard), The Haskell Road to Logic, Maths and Programming (see also this extensive review (PDF)) by Jan van Eijck and Kees Doets is definitely the book for you. Its purpose is to teach logic and mathematical reasoning in practice, and to connect logical reasoning with Haskell programming. And, in my opinion, it does a pretty good job at that. Although it begins with the very basics, it includes chapters on far from trivial (i.e., fun!) stuff like, for instace, corecursion or Cantor sets. And i found amazing how natural it was to express logical and mathematical ideas in Haskell.

But maybe you prefer to learn a bit of applied Computer Science, instead of abstract maths, with Haskell. No problem: just grab a copy of Fethi Rabhi and Guy Lapalme‘s Algorithms, a functional programming approach, which challenges the academic establishment by teaching algorithms using Haskell, that is, in a purely functional context. Revisiting classical (and apparently imperative) algorithms like sorting, tree and graph traversal or dynamic programming methods under a functional light is a refresing experience, and an eye-opener: the fact that all the typical algorithms are covered in just 256 pages is a testament to the authors’ claim that functional programming leads to smaller, clearer and more elegant program. Besides, as you probably know, Haskell features lazy evaluation, which poses entirely new (and pretty instructive) challenges when it comes to evaluating the efficiency of an algorithm.

The seasoned haskeller

fopOnce you’re comfortable with the language and have learnt all about monads, the best thing to do is to study non-trivial Haskell applications. To that end, you can hardly find a better book than The fun of programming, a Festschrift celebrating Richard Bird’s sixtieth birthday. Including thirteen chapters by luminaries in the field, this book describes fun applications on such fun things as musical composition or graphical design, as well as covering advanced programming techniques such as data structures design, interpreters or optimization. Amazing.

I also own a copy of Paul Hudak‘s The Haskell School of Expression, which is often recommended as as Haskell primer. In my opinion, it goes too quickly into the nitty-gritty details of (music and multimedia) implementations to be a good first book, but it is probably a good second book on Haskell programming. But that’s just me: as you can read in the review above, some people have diverging opinions.

The fun never ends…

After all these readings, and a bit more about monads, you’ll begin to feel an expert, and may be interested in more advanced stuff. I’ve got a couple of books reserved for that moment. The first one is The Algebra of Programming, by Richard Bird and Oege de Moor, and its purpose, simply stated, is to show how to calculate programs algebraically using and old friend of ours: category theory, including the bananas that will be the main theme of my second post on these matters. There you’ll find and in-depth, abstract treatment of algorithmic strategies with an eye of correctness proofs. Although heavy on theory, there are interesting applications of this algebra of programming, like the conversion between binary and decimal numbers in TeX, the best way of drawing a cylinder in LaTeX or good data compression algorithms. A slight nuisance is that this book uses an old Haskell dialect (a precursor, actually) called Gopher, but the conversion to modern notation is pretty straightforward.
Finally, anyone serious about algorithms and data structures should read Chris Okasaki’s Purely Functional Data Structures, and amazing tour on advanced algorithimcs using functional programming languages, with source code in SML and Haskell. The exposition is extremely elegant and synthetic, and i’ve spent many, many hours immersed in its 220 pages (i can’t think of any other programming book with a better signal to noise ratio, really).

That’s it. I just hope that 48-hours days are invented any time soon. Happy reading!

Driving iTunes with Scheme, with a fold tutorial and a Haskell book

In this pretty detailed tutorial, Jim Ursetto puts his Cocoa/Chicken bridge to work. Jim noticed that some of his music files were forgotten by iTunes, and wanted to reimport them without losing any metadata. His article

documents my attempt to do just that by building an application in Chicken Scheme, using the bindings to Objective-C and Cocoa provided by the objc egg. It’s targeted at the intermediate Scheme programmer, who may have some experience with Cocoa. It may also be useful to a beginner looking for examples of an interactive development process, and to a non-Scheme user for the same reason.

Jim has taken the time to document also the program’s design and coding processes, so you’ll not only learn about Cocoa or how to use the Scheme bridge, but also about property lists parsing, symlink creation or exception handling. In addtion, you will have the chance of looking over a fellow programmer shoulder having fun for a while.

Programming in HaskellIt’s a long read, but a very good one. And just in case you don’t get to the end, don’t miss Jim’s last recommended reading: a tutorial on the expressiveness and universality of fold, by Graham Hutton. Graham, by the way, happens to be a Haskell and functional programming erudite and professor, so you may be interested in his publications, including the forthcoming book Programming in Haskell, whose first five chapters are available in PDF here.

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Contracts, Felleisen and Elements of Style

I’ve found a very interesting Guide to PLT Scheme Contracts in a temp directory of Matthias Felleisen’s site. It’s a very recent “incomplete draft”, but it’s already a nice reading for all of you PLTers interested in the nice Design by Contract extensions found among the many goodies included with PLT Scheme.

Matthias’ site, by the way, is full of very interesting stuff, including the quotations in its front page or the awesome list of publications.

I also found, browsing around his site, an unexpected jewel: a link to Strunk and White’s Elements of Style, which points to the book’s full, searchable text. Before you ask what this has to do with programming, let me leap onto a giant’s shoulders:

Besides a mathematical inclination, an exceptionally good mastery of one’s native tongue is the most vital asset of a competent programmer.

Edsger Dijkstra, How do we tell truhts that might hurt?

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The Lisp Dictionary

William Bland announced yesterday The Lisp Dictionary, a Lisp-centric document searching facility where he has indexed the Common Lisp HyperSpec, PCL, Successful Lisp, and SBCL‘s documentation strings, plus example code taken from PAIP and PCL. All mixed together in a simple and elegant interface.

(As an aside, William is the author of a very fun Linux module, Schemix, which embeds a Scheme interpreter right into the kernel, although this days he recommends Movitz, a Common Lisp x86 development platform directly “on the metal”.)

If you’re an Emacs user, here’s an elisp function (courtesy of a c.l.l poster named Nick), to search the Lisp Dictionary without leaving your editor:

(defun lispdoc ()
  "searches for SYMBOL, which is by default the symbol
currently under the curser"
  (let* ((word-at-point (word-at-point))
	 (symbol-at-point (symbol-at-point))
	 (default (symbol-name symbol-at-point))
	 (inp (read-from-minibuffer
	       (if (or word-at-point symbol-at-point)
		   (concat "Symbol (default " default "): ")
		   "Symbol (no default): "))))
    (if (and (string= inp "")
             (not word-at-point) 
             (not symbol-at-point))
	     (message "you didn't enter a symbol!")
	 (let ((search-type 
			  "full-text (f) or basic (b) search (default b)? ")))
	  (browse-url (concat ""
			      (if (string= inp "")
			      (if (string-equal search-type "f")

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On Lisp On Line and new PLAI

I’m sure i don’t need to comment or recommend Paul Graham’s On Lisp. Nor tell you that it’s available from the author’s site in PDF format. However, you may be (as i was) unaware that there’s an on line HTML version, complete with a search box and settable CSS. I also routinely install it in texinfo format, for easy reference inside Emacs.

On a related note, i’ve also recently updated my copy of Shriram Krishnamurthi‘s Programming Languages: Application and Interpretation, a wonderful book that Shriram uses in his Programming Languages course at Brown University. It covers almost every single interesting corner of PL-land, including interpreters, laziness, recursion, continuations, garbage collectors, type theory, declarative programming or macros. The book commences with an invitation:

I think the material in these pages is some of the most beautiful in all of human knowledge, and I hope any poverty of presentation here doesn’t detract from it. Enjoy!

Needless to say, poverty of presentation is hardly to be seen in this excellent work.

Happy reading.

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Programming in Smalltalk for Spanish readers

Squeak, a World to LearnDiego Gómez Deck is finishing a new book entitled Programando con Smalltalk (Smalltalk Programming), which guides readers new to Smalltalk (but not to programming) into the use of the language and the Squeak environment. The book will be published under a CC license, and its drafts are available online. I just skimmed over the latest draft, but seems a very interesting reading (if you read Spanish, that is; translating Diego’s book to English would be an interesting project). Diego has already coauthored a previous Spanish Squeak book, which was published last year: just click the image of its nice cover for more info.

This book joins the uprising of Squeak’s popularity in Spain, driven by its being used by the local government of Extremadura as the platform for some of its projects. The last one consists of an interactive educational and reference tool that will let users of the Extremadura’s Regional Net to know more about a bunch of topics on physics, chemistry, biology, ecology or society, to name a few. Actually, the tender is still open, in case you feel like trying. Cees’ Blog provides the necessary info (this time in English), including some reasons to not really wasting the time applying.

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