A view from the hill

When I got a Handspring Visor (a Palm Pilot offspring) roughly ten years ago, I was amazed about all the nice things you could do with the device. I even wrote a German version of the visor linux howto, although I never really finished it. What I especially liked was the possibility to install a ssh client and use it to connect on the push of a button to my workstation -- which I took to good use several imes when my Xserver went beserk. Unfortunately, over time the major incentive to use the thing, syncing calender and address book vanished, as it turned out to be a major hassle when the main calendar to sync with was Lotus Domino. So, since some years my trusty Visor has only gathered dust. But even back in 2000, it was clear to me that the Palm Pilot would only be the starting point and that at some time in the then-unknown future, we would have small devices that would allow issuing phone calls, taking pictures, listening to music as well as providing the "usual" features of handhelds.

Back then, I didn't really think about when exactly that device would arrive but I think the time has come finally. Some days ago I bought a Nokia N900, which is a mobile device running Maemo on top of a Linux kernel on an ARM platform (see this overview of the hardware for more details). This is really a neat little gadget which is really as close to my ten year old dream as you can get: It comes with mobile phone capabilitiy, UMTS and wlan connection, 5MP camera, media player, RSS feed reader, etc. and also has a quite usable sliding keyboard. It's not really a mobile phone but a pocket computer which you can also use to call people with, which shows for instance in that most applications require the device to held in landscape position.

Of course, what's most interesting to me is the software on the device. Basically, Maemo 5 is a linux distribution based on Debian technology, e.g. apt/dpkg and friends work as expected. You don't get all of your favourite linux applications of course, but still there are quite a lot of the regular stuff you would expect. This includes the mobile version of Firefox, Fennec, vim, OpenSSH (client and server) and even Emacs. Being the geek that I am, nearly the first thing I did was a remote login via ssh from my workstation on the N900 (also see this overview of USB networking on the N900). Native maemo applications are typically developed with Python and GTK, although that is probably going to change for Maemo 6 (Nokia has announced it favours Qt over GTK). The community seems quite active, too: just shortly, a port of Clisp (a Common Lisp compiling to byte code) was announced (including a running Swank backend, so you can connect from your development Emacs remotely), although I imagine that the development environment for Python is, generally speaking, more advanced (for Maemo development, this is). I haven't looked any closer into developing for Maemo up to now, but it surely looks interesting.

ObTitle: Gossip, "Music for men"

Via Lambda the Ultimate I came across an interesting article On data abstraction, revisited by William Cook, written for OOPSLA'09. It carefully dissects abstract data types from objects. All theoretical considerations aside that distinguish ADTs and objects, there is one common characteristics given by Cook: you can't inspect the concrete representation of the data you're abstracting. This is in itself interesting and reminded me of two rather practical things.

First of all, I was reminded of a section in Bob Martins Clean code development which discussed the idea that you should on the one hand follow the rule "Tell, don't ask" and on the other hand have data access objects that don't have much, if any behaviour besides providing data. This is obviously directly related to Cooks article: if you want data abstraction, you shouldn't really provide any way to allow other objects/methods to access the internal representation. This somewhat also forbids getters as this is likely to lead to leaky abstraction, since more often than not programmers simply return the value of some data field, directly exposing the representation chosen. Now, please note that this does not necessarily follow from Cooks article, as it is possible to design getters in such a way that you can return whatever you want for a getter method, i.e., you can return a desired return type or an object satisfying a particular interface. For me, the relevant point here is the way of thinking about the kind of object at hand: do I want some behaviour (aka Cooks objects) or do I want a data sink. In the former case, and in line with what is suggested in the clean code book, it is arguably the best way to tell the object to do what is necessary rather than to inspect (get) the data it holds and do it externally in some other object/method. But even in the latter case, I think it is important to give great attention to hiding the internal representation from external access and to only allow very focussed access to the data itself. It could and has been argued that restricting the access to the stored data via getter methods is tedious (see e.g. the discussion in getters/setters/fuxors) and that allowing public access to members is allright, but looking at the issue from a data abstraction point of view it simply boils down to the question whether you want or need data abstraction or not.

Second, I've recently seen these two postings on the merits of the Zope Component Architecture: The emperors new clothes and the reply The success of the ZCA. Malthe asks why one should use the ZCA to override the use of a particular implementation with another instead of using some kind of reloading (or rather says that the latter is the preferrable approach). Relating this to Cooks article, Malthe could be paraphrased roughly as: we have ADTs all over the place and we only should allow only one implementation per ADT (this is what the type system would guarantee in other systems). If you want another implementation (of some interface, as Cook shows for his objects), you should reload the object defintion with the one you want. The use of the ZCA, however, is directly related to the very idea of object oriented programming in the way Cook defines it: you only have interfaces that are the relevant defining characteristics of objects (values) and hence, the use of the ZCA is the way to deal with multiple implentations in Zope (or Python). For me, all I can say is that I'm happy that the ZCA and hence the ability to easily intermingle multiple implementations is there (then again, with me reading computer science theoretic articles I'm arguably not of the angry web designer type whose benefit Malthe is arguing for).

There is another, more puzzling aspect of the article to me. After some considerations, I have to conclude that of all OO languages I happen to know, it's really only Java that seems to be object oriented in Cooks view of the world. This is because in Java, you can define a method to return objects satisfying an interface. In addition, in dynamically typed languages like Python, Ruby, or CLOS, you could try to come away with duck typing, but it's arguably only Python which tries to take it to the heart (for instance in CLOS, most values you're gonna deal with are non-CLOS values and you even have an ETYPECASE statement, which is a switch-statement on type distinction). Funny enough, Cook finishes his Smalltalk analysis with the statement that "one conclusion you could draw from this analysis is that the untyped lambda calculus was the first object-oriented language". But besides the point how some language is "more OO" than another, there is also to the point that in order to program truly object-oriented, you shouldn't (and in Cooks world really can't) rely on type checks, because the whole point of using objects as data abstraction is to rely on behaviour.

ObTitle: Dial M for Murder, "Fiction of her dreams"

Betrand Mathieus blog article on cleaning up trailing whitespace comes in handy for me as I've frequently run into problems with the Python test coverage tool stumbling over trailing whitespace. It also reminded me of an emacs snippet I recently installed to detect a mix of space and tabs in my Python buffers -- I do set (setq indent-tabs-mode nil) in my .emacs for python-mode, however, I still occasionally somehow manage to insert some tabs in my source buffers. So I came up with the following snippet which validates that a buffer in python-mode doesn't contain any tabs. It's hooked up with the very general write-file-hook, but there is no python-specific hook on saving buffers. In case the buffer does contain any tab, it will leave the point (the place where your cursor will be) at the fount tab.

; code snippet GUID 32F94179-A86B-4780-8645-8A526BD8533A
(defun no-tab-validation (buffer)
  (interactive "bValidate buffer:")
  (save-excursion
    (unless (equal (buffer-name (current-buffer)) buffer)
      (switch-to-buffer buffer))
    (if (re-search-forward "\t" nil t)
	(error "Buffer %s contains tabs" buffer))))

(defun py-tab-validate-on-save-hook ()
  (when (equal mode-name "Python")
    (no-tab-validation (buffer-name (current-buffer)))))

(add-hook 'write-file-hook 'py-tab-validate-on-save-hook)

Enjoy.

Update: I should clarify that my previous reference to (set-indent-tabs-mode nil) is just a local function around setting the variable indent-tabs-mode directly. I use it also for a local toggle function, like so:

;;; inhibit tabs in some modes
(defun set-indent-tabs-mode (value)
  "Set indent-tabs-mode to value."
  (setq indent-tabs-mode value))

(defun toggle-tabs ()
  "Toggle `indent-tabs-mode'."
  (interactive)
  (set-indent-tabs-mode
   (not indent-tabs-mode)))

(defun disable-tabs-mode ()
  (set-indent-tabs-mode nil))

(add-hook 'sgml-mode-hook 'disable-tabs-mode)
(add-hook 'xml-mode-hook 'disable-tabs-mode)
(add-hook 'python-mode 'disable-tabs-mode)

ObTitle: Bloc Party, "Weekend in the city"

There seems to be a roaring discussion about a talk by Robert "Uncle Bob" Martin at this years RailsConf, which mainly seems to be concerned with the question (raised by a quote appointed to Ward Cunningham) whether languages such as Smalltalk make it too easy to create a mess. Languages such as C++ would penalize the mess at least by longer compile times.

As Giles points out that's an old argument, which I too have heard too often in the past about dynamic languages, regardless whether we're talking Smalltalk, Ruby, Lisp, Python or Perl. And the anti-dote was always the current idiot language of the date, i.e. Visual Basic at its high time, Java or C# (for those who considered C or C++ to be too dangerous). Please note that I'm not at all saying that users of those languages are idiots, but those languages are particularly claimed to be usable by idiots, too. This approach to languages or to their classification does a great job of misrepresenting programmers regardless of the language of their choice. It makes the bold claim that there are programmers that are idiots and that it's possible to design a language that even those idiots can do their jobs. And the exaggeration is that its only good business sense to enforce the use of those languages for all development projects, because, as we all know, there are more idiots than intelligent programmers out there, right?

The only problem with this claim is that human stupidity is probably the only thing larger than the universe, if you make something idiot proof, nature will quickly make a better idiot. To put it a little less cynical, to err is human. And there is value in people making mistakes. As for instance, Tom DeMarco claims in his book "Slack" it's a particular good way to learn. Bob Martin tries to sell excessive testing (which isn't particular surprising, giving his background) as one safety guard to which James Robertson responds that this is not always necessary:

Yes, tests are useful. But, the debugger is not something to be feared. Rather, it's a great tool to be used in order to have the computer do all the memory work for you. I can get a lot more done by working with decent tools like the Smalltalk debugger than I can by assuming the doc is good and writing tests that just help me a whole lot less than you might think.

I can relate to this quote, being a fan of interactive development that languages like Lisp or Smalltalk made popular. But I think James is missing the point: tests are not only helpful during development. Sure, using an interactive approach helps getting the code run but does it help to come up with a clean design? Looking back at some code, I can assure you it doesn't, quite to the contrary it's a way to get a working solution quickly, not cleanly. This doesn't make the debugger or the REPL less valuable: using it you can quickly establish your tests, debug your tests, whatever. This is exactly where the value of dynamic languages shines and those "silver-bullet" idiot languages are still behind, regardless of their shiny IDEs.

But the real point summing up the discussion so far is the old Frederick Brooks quote: There is no silver bullet. It's good to be careful and to use the tools at your hands to help you avoid the big mistakes. As Paul Graham puts it for OOP: "For programs that would have ended up as spaghetti anyway, the object-oriented model is good: they will at least be structured spaghetti." But in the end you have to learn how to avoid the mess in the first place and no language and no tool can do that for you.

ObTitle: Dexter Gordon, "Ballads"

Drew Campsie announces ucw-core, the next generation of Uncommon Web, a continuation-based framework for web applications written in Common Lisp. It's the first major announcement since Drew took over development lead of ucw and it seems to focus on establishing a core library of basic technology on top of which other functionality can be implemented (e.g. functionality like those offered by the ucw-ajax). To me as a UCW user this sounds like great news, since I had the impression that ucw seemed to linger in a state of void over the last year or so.

But even more interesting is that ucw just seems to follow a certain trend. For instance, according to the announcement that Ruby on Rails and Merb will merge, one goal is that Rails will be retrofitted to make it easy to start with a “core” version of Rails (like Merb’s current core generator), that starts with all modules out, and makes it easy to select just the parts that are important for your app. The main aspect of such development (at least I hope so) seems to be best described by one of Django design goals): A fundamental goal of Django’s stack is loose coupling and tight cohesion. The various layers of the framework shouldn’t “know” about each other unless absolutely necessary. The python folks have even gone so far as to write down a web server gateway interface specification (WSGI, a quite minimalistic specification).

It will be interesting to see whether there's going to be even more unification, maybe even across language diffferences. I'm not too certain that such an unification would necessarily be a good aim; as always there are probably as many benefits as downsides to it. For instance, a common specification certainly lowers the learning curve for people switching frameworks while at the same time may stiffle further development. Then there's the fact that the different frameworks have different approaches which are certainly reflected in their APIs: for instance, Django explicitly tries to avoid magic at all cost while there's traditionally a lot of magic going on behind the scenes of a Rails application. I'm also not sure where exactly one should draw the line between common "core" functionality and additional "batteries". As an application designer it's probably most important that there is such a line at all so that you can easily pick your poison without having to buy everything.

I've become a python programmer, too, lately, due to a job change. Python is a fine language so far, although to me it's mostly just like Ruby, though with even less functional flavour. However, just as with Ruby, I'm really missing slime, the superior lisp interaction mode for Emacs, when hacking python code. I could now start to write down a list of things I'm missing (which I've intended to do), however, Andy Wingo spares me the hassle, as he has just written an excellent article on slime from a python programmers view.

However, I would like to elaborate a little on the main difference for me: the client/server socket approach of slime. Let me briefly recapulate what this implies: slime consists of two parts, a client written in Emacs lisp and a server written in Common Lisp (AFAIK there is at least also an implementation for clojure, maybe also one for some scheme implementation). In order to use slime in it's full glory, it's hence required that you have a common lisp process running which in turn runs the slime server part. If you now fire up slime, you'll get an interaction buffer over which you can access the REPL of the lisp process, which in python would be the interpreter prompt. You can then interact with the lisp process, evaluating pieces of code from your lisp source code buffer directly in the connected lisp process. What is incredibly useful for me is that you can not only start a new lisp process but also connect to an already running lisp process, given that it has the slime server started (this is obviously mainly useful if the lisp implementation you use has multi-threading capabilities). I use it to connect to a running web server application, which I can then inspect, debug and modify. Modification includes redefinition of functions, macros and classes, which of course is also a particular highlight of Common Lisp. I would like to cite a comment of the reddit user "fionbio" he made wrt. to the linked article: In fact, Python language wasn't designed with lisp-style interactive development in mind. In CL, you can redefine (nearly) anything you want in a running program, and it just does the right thing. In Python, there are some problems, e.g. instances aren't updated if you modify their class. Lisp programmers often, though not always, refer to various things (functions, classes, macros, etc.) using symbols, while Python programs usually operate with direct references, so when you update parts of your program you have much higher chances that there will be a lot of references to obsolete stuff around.

To complement Bill clementsons excellent article series on slime a little, I'm going to describe how I'm using/configuring python-mode to make it match my expectations a little closer. Essentially I would like to access my python process just as I would with slime/Common Lisp, but that's not possible. The reason, btw., is nearly unchanged: I need to code on a web server app (written in Zope) which may not even run on the same machine I'm developing on. Let's first cover the simple stuff: To enable a reasonable command interface to the python interpreter, I require the ipython emacs library. If the python interpreter runs locally, I also use py-complete, so that I can complete my code at least a little. Unfortunately, this breaks when the python interpreter doesn't run locally, because the py-complete needs to setup some things in the running python process, which it does by writing to a local temp file and feeding it to the python process. Unfortunately, the code in py-complete lacks customizability, i.e., you can't specify where that temp file should be located -- I should be able to come up with a small patch in the near future, which I will add below. Finally, I also require doctest-mode as a support for writing doctests, but that's not really relevant.

Now, on to the more involved stuff: I introduce some new variables and a new function py-set-remote-python-environment, which uses the those variables to do a remote call (via ssh) to python. This at least allows me to do things like setting py-remote-python-command to "/home/schauer/zope/foo-project/bin/instance" and py-remote-python-command-args to "debug", so that I can access a remote debug shell of my current zope product. That alone will only allow me to fire up and access the remote python, so I could now develop the code locally, having it executed remote. More typical though is that you would also want to keep the code on the remote machine, too: for this I use tramp, a package for remotely accessing files/directories from within emacs. In combination, this allows me to edit and execute the code on the remote machine. It is still nowhere near what is possible with slime, but at least it allows me to persue my habit of incremental and interactive development from within my usual emacs installation (i.e., it doesn't require me to deal with any Emacs related hassle on the remote machine).

;;; python-stuff.el --- python specific configuration

(when (locate-library "ipython")
  (require 'ipython))

(when (locate-library "doctest-mode")
  (require 'doctest-mode))

(defvar py-remote-connect-command "ssh"
  "*Command for connecting to a remote python, typically \"ssh\"")
(defvar py-remote-connection-args '("user@remotemachine")
  "*List of strings of connection options.")
(defvar py-remote-python-command "python"
  "*Command to execute for python")
(defvar py-remote-python-command-args '("-i")
  "*List of strings arguments to be passed to `py-remote-python-command`.")
(defvar py-remote-python-used nil
  "Remember if remote python is used.")

(defun py-set-remote-python-environment ()
  (interactive)
  (let ((command-args (append py-remote-connection-args 
			      (list py-remote-python-command)
			      py-remote-python-command-args)))
    (setq py-python-command py-remote-connect-command)
    (setq py-python-command-args command-args))
  (setq py-remote-python-used t))

(when (locate-library "py-complete")
  (autoload 'py-complete-init "py-complete")
  (defun my-py-complete-init ()
    "Init py-complete only if we're not using remote python"
    (if (not py-remote-python-used)
        (py-complete-init)))
  (add-hook 'python-mode-hook 'my-py-complete-init))

Joey seems to have inspired a "list of programming languages you know"-contest over on planet.debian.org, so this is mine:

1. Basic (forgotten)
   I've started using Basic on the Commodore C64 and have used it considerably, apart from the intrinsics of peek and poke, which some would claim was what Basic on the C64 was all about. I also used Basic on the Apple II at school, but was spared any further need to use Basic.
   
2. Cobol (forgotten)
   I remember my old computer science teacher bringing white and green prints on endless paper and teaching us the joys of Cobol. Having used Basic before, it looked somewhat suspicious but not too alien. Fortunately, we only had to solve some simple problems on paper, as the Apple II only had .... DBase II, I think.
   
3. Pascal (forgotten)
   (Turbo) Pascal was the language of choice in the first semester at the University of Koblenz at the start of the nineties. I've did what I had to do in it, but never really liked it. From the occasional look I throw in Wirth's algorithms book I know I can still read it, but the language looks just as baroque as the copy of the book I have.
   
4. Prolog (forgetting)
   I've really done a lot in Prolog, being first exposed in the second semester to it. I remember to marvel at some guys who grokked the language at first usage in the initial course -- to me, having used only imperative languages up to then, it was a mistery. I still think Richard A.O'Keefe's book "The Craft of Prolog" is among the best CS books.
   
5. C/C++ (forgetting)
   About 1992, I somehow got interested in object-oriented programming. Free software was still unknown to me, so I bought a student edition of Turbo C++ and some Addison-Wesley book and of I went inventing another wheel. At the time, I also had to do some C hacking for some course at the university, involving MS Windows programming. I've used C over time in several smaller projects, but would never call myself a C hacker.
   
6. Assembler (forgotten)
   My first exposure to Assembler was with some book for the C64. I was very interested but understood next to nothing. I should program some I/O chip directly instead of just using "load $,8,1"? WTF? Next look was in University, of course. I still know enough bits to be able to grok more or less the output of (disassemble 'foo) of some (tiny) foo-function in CL on an i386-style machine, but that's about it.
   
7. Mercury (had interest in)
   Mercury seemed like a nice successor to Prolog, adding several features of functional languages. I read several manuals, had several installations and never used it for anything.
   
8. Life (had interest in)
   Another possible successor to Prolog, which I've learned about at a summer school for language, logics and information. That's about all I remember.
   
9. XLisp (forgotten)
   My first exposure to Lisp in the context of a course for computational linguistics. The only thing worse than the editor used in the system was the tutor giving the course. A horror of parenthesis is about the only thing I remember.
   
10. Shell scripting (daily usage)
    I think since 1992 or 93 I've been using Unix systems and shell scripts. I no longer can remember whether our Suns dumped you into csh or sh or whatever, but since I've been using Linux systems (since 94), I've been using bash and written bourne shell scripts. Of course, I've also written the occasional csh script abdomination, but "Csh programming considered harmful" was an early lecture.
    
11. Emacs Lisp (forgetting)
    I remember seeing one of my instructors doing nearly miracles with XEmacs and wondering how his fingers could be that flexible -- I know that now. I've written several small utilities in Elisp and keep using it occasionally.
    
12. Common Lisp (improving)
    When I started a student job in 1995, I also started using Common Lisp, using Steele's CLtL2. Having used Elisp before, I no longer was worried about parenthesis. I still keep finding areas I didn't know or used before. And it's a language large enough that keeps you re-learning tricks you thought you knew. Which didn't stop me from giving a course on CL, which in hindsight didn't have the right focus: instead of showing that CL is just as capable of doing whatever you expect, it's also capable of doing you won't expect.
    
13. Smalltalk (interested)
    At the computational linguistics lab in Freiburg, the parser system was implemented in Smalltalk, so when I started there I took a small course in Smalltalk. As I worked more on the knowledge representation side of the system, I only rarely used it, though, so rare indeed, that I never got to do anything serious with the language. I still can read Smalltalk despite it's somewhat unusal syntax and have to do that even sometime.
    
14. Tcl (forgotten)
    We wanted to extend a linguistic annotation written in Tcl, so I bought a book and started digging through the code. Soon enough a student took over the job (and did it rather well), so I started the tiny bits I've learned quite soon. I remember finding the concept that every thing is a string to be rather messy and still see it as a lame excuse for dynamic/weak typing.
    
15. Perl (static)
    For nearly ten years, I had been using shell and/or Emacs to solve any data mangling tasks when I finally gave in and had a closer look at Perl. I still find it amazing how quick and dirty it's possible to solve problems in Perl, but on the other hand I've given up Perl for more complex tasks that require some thought and design, since Perl's syntax and language idiosyncrasies keep leading me to programs I don't even like myself.
    
16. XSLT (improving)
    At about the same time I started using Perl, I also needed to transform a set of XML documents and XSLT was all over the media, so I had a closer look. I dislike the noisy syntax of XSLT and particular the intermix with output elements and it's fever for being a "clean" functional language. But the concept of XPath and the idea of traversing a document via axis I find very compelling.
    
17. make (static)
    For a long time the power of make didn't occur to me. A colleague of mine, however, used it to implement a nifty workflow for document processing, of which I learned a lot of tricks when I needed to mimic it for a different task.
    
18. Ruby (improving)
    When I finally was fed up with Perl, I looked around to find Ruby as a nice halfway compromise between Common Lisp and Perl. It's still fancy and geeky and with Ruby on Rails has a lot of buisness ballyhoo around it, so I hope it will see more use in my current surrounding.
    
19. Java (not interested)
    Like everybody else, I couldn't avoid looking at Java. It seems to be the Cobol of today and as such is the job guarantee today. But Java looks so boring, I can hardly stand it. And this with regard to both the language and the results produced with it. Sigh But still, it's likely that someday I'll going to buy another book (that would be my third Java book, the first being O'Reilly's Java in a nutshell for Java 1.1 in maybe 1997 or so?), since just like Cobol at it's time, avoiding Java is hard ...
    
20. Python (not interested)
    When Python 1.4 hit the scene, there was quite some bubble around it. It burst quickly and as my latest review of the language reveiled last year, it still doesn't seem interesting.
    

Missing in this list is stuff like Scheme, Dylan, Oz, Oberon, Eiffel, Haskell and probably some other "tiny" languages which I looked at at some point in time and really didn't ever took a second look. Of those, I may take another look at Haskell in the future, but currently I have no concrete plans in doing so.