Monday, November 30, 2009

Code beauty, J vs. Mathematica

I drew the equivalent kernel of a smoothing spline in J.

t =: i: 10 j. 1000
y=:(%2) * (^-|t% (%2)) * sin(( (|t)* (%:2) % 2 )+ (pi%4))
plot t;y

This is the Mathematica version:

Sunday, November 29, 2009

The J programming language

Today I went through the first few tutorials of the J programming language. J is a treat. The human language has many devices that keep things short and explicit. While in context-oriented programming people are still wondering how to properly identify and model the "context" of a statement, natural language already goes and changes the behaviour of nouns by specifying them more precisely with adjectives. Compare that with modern object-oriented programming languages, which only have nouns (classes) and verbs (methods) at best.

The J language tries to harness the power of the natural languages by providing nouns, verbs, adverbs, conjunctions, and comparatives. I'd love to see an OO version with adjectives.

The tutorials are splendid and the IDE helpful, which I won't elaborate on because James Hague wrote such a nice piece about the fact. Oh, and he raves about the built-in plotting. Here's some turtle geometry, similar to an example that they provide:

The source code was:
show repeat 20;'point (n =: n+1) fd 1 rt 15'[n=: _2
to 'goreturn a b';'goto b goto a'
to 'goreturnall a'; 'goreturn for a,.i.20'
show goreturnall for i.20

The article is over. Just one last thing: There's a funny glitch in the tutorials. The tutorials assume that you have some familiarity with Hilbert matrices and alternating binomial coefficients. But you are not expected to know how to handle a mouse:
The color window can be moved away from text that it may obscure by clicking on the top bar, holding the button down, and dragging it to a new position before releasing the mouse button –– Chapter 2, lesson 2 in the J tutorial

Saturday, November 21, 2009

And it's done, Phexample has no more lolcats

Image from Wikipedia, see for the author. CC license.

Lolcats have left the building, Phexample reads easier now.

Stack new isEmpty should not be true.

To get a meaningful error message out of this test, you're faced with a small dilemma. The Phexample framework lies in the should method, thus, for all that should sees, it is called on true, so the test might as well have been

true should not be true.

Now, to squeeze a reasonable error message out of this, such as "isEmpty should return false, but got true," it helps finding the unexecuted code snippet in the caller. Thus, the execution depends on who called you. Maybe not perfectly object-oriented, but context-oriented! There we have a new buzz-word: COP, context-oriented programming.

I learned a few things on the way: Bytecodes in Smalltalk have different sizes, thus you can't just walk backwards from where you are. The containing method must be read forwards, and once you hit the position of the current execution, you know you're a bit too far. Also, you find the current stack frame using the pseudo-variable thisContext, though there are some performance issues with it.

By the way, you can't really ice and copy the stack (someone forbade it in the source, for whatever reason), you're analyzing it as it is being used for the current computation. A bit scary, but it works quite nice. Pharo ftw! Try this in JavaScript!

Get the latest version of Phexample at SqueakSource (there's a Gofer-Script on that page that will do the downloading for you!.

Thursday, November 19, 2009

Phexample's lolcats syntax

In this post I'll clear my throat on what there is to come. The number one criticism of Phexample is that Phexample sometimes reads like lolcats, because real code that asserts that a stack be empty reads like

stack should not be isEmpty.

The complaint feels like an instance of the complaint of how stupid it is that in OSX you need to drag CDs to the waste bin to eject them, or how in Windows the bin stands on the desk. Of course the metaphor is broken there, but you only notice it because the metaphor works great.

And now you compare that to the usual alternative, which is assert. The first thing you know about assert is that nobody can remember which one is the expected and which is the actual value (I'll take this fact and some of the below discussion from Josh Graham's discussion of the assert syntax). We're talking about assertEquals(stack.isEmpty, true). Or the other way around. I certainly can't remember that either.

In Java, improvements have been suggested:
assertEquals(expected(true), actual(stack.isEmpty());

I find that while Phexample does not allow you to express your examples in a way that completely parses as natural language, it certainly reads easy enough and gives a natural and easy distinction between the expected and the actual.

So there's my analogy: no other testing framework is required to express its tests in a way that perfectly parses as human language. Only because the tests already look so close to perfection is it that people single out the mismatch and decry it. I don't think this is an interesting problem worth solving at all.

Yet, the criticism follows Phexample wherever it goes, so I'll try and allow phrases like

stack isEmpty should be true.

The difficulty in making the above code work is that the testing framework is only activated after isEmpty was evaluated already. Which means that it isn't in the stack anymore, so we need to analyze the source code to find out which method caused the failure to display a meaningful error message.

Wednesday, November 4, 2009

Telling other people how to install your code

Previously, I created dirty ScriptLoader tricks to make it easier for others to download my code.

I am pleased to find out that Gofer is even easier than my dirty tricks, well without being a dirty trick: Gofer on Lukas's blog.

Phexample, because examples expand on one another

Imagine you want to test the Stack class, and your first test just
creates a test and checks if it's empty.

Then in your second test, you create the same empty stack, but now
push an element 'apple' and check if the size is one.

Then in your third test, you do all the same, and then you pop the
element and check that it is an apple.

Wouldn't it be great if you could write your test cases such that they
could expand on one another? If you didn't need to copy paste the code
of the previous test and just say that you require the previous one!

Well, that's what PhExample lets you do. And as a bonus, tests are
ignored if the test they expand on does not pass. This gives you less
failed tests, because examples are executed only if the examples they
expand on pass too! That gives you the simplest failing examples in
your set to look at!

And best of all, you can run all examples with ye old TestRunner!

The example discussed above would read in code as follows:

EGExample subclass: #ForExampleStack

"Create the empty stack"
| stack |
stack := Stack new.
stack should be isEmpty.
stack size should = 0.
^ stack

"Push one element"
| stack |
stack := self given: #shouldBeEmpty.
stack push: 42.
stack should not be isEmpty.
stack size should = 1.
stack top should = 42.
^ stack

"And pop it again"
| stack |
stack := self given: #shouldPushElement.
stack pop should = 42.
stack should be isEmpty.
stack size should = 0.

Find the code at

You can install it as follows using Gofer:

Gofer new
squeaksource: 'phexample';
addPackage: 'Phexample';

The repository is write-global, so feel free to drop your ideas!

PhExample is based on JExample by Lea Haensenberger, Adrian Kuhn, and
Markus Gaelli. See JExample