Author: grant

Caveats of Object Creation using Closures

At one time or another you have probably heard the claim made that since you can utilize closures while programming in Lisp, there is no need to utilize an object system. That claim is sort of a half-truth. While closures are the language construct that allow you to create objects, they certainly don’t provide you with all of the object oriented programming language features that you would expect. Instead, you need to implement those features yourself.
The question was posed on the PLT discussion list. Some very good points were made about the issues you must address when implementing such an object system yourself, along with a pointer detailing how the issues are addressed in PLT Scheme.

Disciplined Thought: A Programmer's Friend

This post on the PLT discussion list reminded me of me. There was a point where my interest in programming languages was more about what you could do with a language, without much of an emphasis on the why you would want to do such a thing. While you can do a lot of interesting things in different languages, there is often more value when there is reason, or vision, of why you would do those things. From my perspective, most languages have, at one time or another had some guiding vision or force behind them.
Eiffel has Bertrand Meyer saying “Everything is an object, and be static about it” and C++ has Bjarne Stroustrup saying “Keep it fast, keep it generic”, Scheme “Programming languages should be designed not by piling feature …”. Ruby has Yukihiro Matsumoto saying “It makes sense to me, if you don’t like it, see you later!”. Consequently there are a lot of really “neat” things you can do in Ruby, but it is not always obvious to me why you might want to do those things (I’m excluding the obvious ones so give me a break on those). Mats knows, and if you don’t “get it” oh well! The vision, or reason, extends all the way from the macrocosm of the entire language to the microcosm of its individual features.
Programming language features are there for a reason. While I will always find individual features interesting in terms of what you can do, one of my goals as a programmer is to always study with enough discipline to understand why such features exist.
As a programmer it is your duty to understand those features before utilizing them. Matthias’ reply to this post provides an excellent example of the conciseness and clarity that are the fruits of such discipline.

Type Conversion with Eiffel

If you are going to utilize the Object Oriented paradigm for implementing your system, you ought to do yourself a favor and learn the Eiffel programming language. Why?
Take all of the things that are not included in your statically-typed OO language of choice because they are “too hard to understand”, and visit them in Eiffel. Not only does it have all of those features, but it makes them easy both to understand and utilize.
Read about type conversion, for example. What a wonderful language feature. You can even use tuples!
You will be left scratching your head, wondering why no one else has features like this (among many others).
Eiffel is really a gem of a language!

Nonstandard Interpretation with Scheme

In response to this excellent blog post by Dave Herman, Jay McCarthy pointed the reader to this interesting paper about creating a language construct that allows you to modularly redefine how your code (that you may or may not have written) gets evaluated (in other words, nonstandard interpretation).
Nonstandard interpretation

is a powerful and useful construct that supports such tasks as tracing, security logging, sandboxing, error checking, profiling, code instrumentation and metering, run-time code patching, and resource monitoring.

Obviously, these things aren’t new features. You can probably already perform nonstandard interpretation using your language of choice.
The interesting thing about this approach is that rather than performing compile time environment or code manipulation, a new language feature is applied to perform the non standard interpretation at runtime.
While both will get you to the place that you want to go; only the latter offers you an opportunity to build a conceptual framework for understand how you reached your destination. Neat!

Distributed Programming in Scheme

Here are two places to start with distributed programming in Scheme:
Termite
Dimitris Vyzovitis’s patch for revision 8983 (of trunk) in PLT Scheme
Addendum 03/21/08

  • Dimitris’ patch for additional mailbox functionality.

Addendum 04/26/08

Addendum 06/24/08
I’m pretty sure this patch has made it into the main source branch.

BarCamp in Wisconsin

Last year some of my friends and I both attended and presented at Barcamp Milwaukee. When you have a bunch of people coming together to discuss things about which they are really passionate, well, you can’t beat it. It was a lot of fun, I met a lot of wonderful people, and even made some new friends. You can watch a video about that event here.
I just heard the news that BarCamp Madison #2 is getting lined up. Here are the details:
The Home Page
The Google Group

Encript-ing Scheme

Enscript is such a versatile and helpful tool.

Here is how I use it to pretty print Scheme code: 


enscript --landscape --columns=2 --highlight=scheme --borders --line-numbers --output=.ps .ss

Addendum: 03/06/09

Here is the direct link for the GnuWin32 download of Enscript.

Addendum: 03/08/09

Here are my new favorite settings for rendering code with this excellent program: 


enscript --word-wrap --underlay=Underlay --ul-gray=0.9 --line-numbers --
landscape --highlight=scheme --columns=2 --borders --output=test.ps C:\collects\wisdomandwonder\resume\latex-renderer.sls

DrScheme: Insert Lambda Template Keybinding

DrScheme provides a very versatile keybinding system. Out of the box you get bindings that make it very easy to navigate and even refactor your code. One keybinding, insert-lambda-template, works by surrounding the selected code with a lambda function. By default, insert-lambda-template uses the lowercase lambda symbol λ rather than the word lambda. As DrScheme encodes its files in utf-8 it has got no problems with this (in fact DrScheme has shortcuts for inserting most other Greek characters), but if you use other tools to edit or process your source code you may find that they (quite disappointingly) choke on it. For that reason, I wanted to modify the keybinding so that it would use the world lambda rather than the symbol. There are two ways to go about doing this.
The first involves modifying the source code of DrScheme itself. This sounds harder than it is as it doesn’t even involve downloading the source code. When you install DrScheme, it includes a number of source files used to customize itself. If you wanted, you could look up this keybinding, change it, and re-run the setup program. I don’t like this approach, though, since it forces the user to re-build part of the program. That leaves us with the second alternative, a custom keybinding.
A custom keybinding is easy to implement and add. To write it, I copied the definition of insert-lambda-template and changed the lambda symbol to the word lambda. Next, I went through DrScheme’s Edit->Keybindings menu to select Add User-defined Keybinding. That is all it takes.
My keybinding file can be downloaded here.