Also known by the longer title: I Sure Hope Zero-Install Succeeds, Or Else We Might All Give Up On Package Managers Entirely.

If you’ve tried to run any of my software lately, you may have noticed that it’s all distributed and packaged via Zero-Install. I’ve posted about how awesome it is, but that was just an initial impression - I’m now familiar enough with the system to expand on those impressions.

After reading that the distros have killed python yesterday, I felt compelled to write in a little more detail how zero-install solves this and many other problems right now, across platforms and languages, and for much less effort than the current packaging practices.

ItsAllText has long been one of my most useful firefox extensions. It allows you to edit the contents of a <textarea> in an external editor (i.e. vim, emacs, etc) and insert the results back into the web page.

I’ve been having trouble with itsalltext, so I scoped out other alternatives. One such extension is TextAid for chrome (Edit with Emacs is another, which thankfully you can use with vim despite the name ;)).

The funny thing about chrome extensions is that they’re not allowed to spawn new processes, which injects a large portion of awkwardness into an extension whose main goal is to spawn your text editor. The workaround is to run a server (locally) that receives a POST request with some text content. The server then spawns your favourite text editor and waits for you to edit its contents. When you’re done, the new text is send back as the response body. It seems a rather roundabout mechanism, but it’s nonetheless kind of neat. And entirely necessary to fit in with chrome’s security model - the chrome extension is just making a long-running ajax call.

So anyway. I took the python server from the emacs_chrome project, cleaned it up, added multithreading so you can edit multiple files at once, and packaged it all up as a 0install package (yep, I still love 0install). You can get it here, if you are ever in the need for such an outrageous piece of software.

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Combining both stop motion and light painting - I can’t imagine anything more fun (and time consuming)

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So the other day I had a list of (html) elements, and I wanted to get an array representing lines of text. The only problem being that some of the elements are displayed inline - so I needed to join those together. But only when they appeared next to each other.

I would call the generic way of doing so group_sequential, where an array is chunked into sub-arrays, and sequential elements satisfying some predicate are included in the same sub-array. That way, my predicate could be :inline?, and I could join the text of each grouped element together to get the lines out.

For example, using even numbers for simplicity:

[1,2,3,4,6,8,5,4,4].group_sequential(&:even?)
=> [[1],[2],[3],[4,6,8],[5],[4,4]]

Here’s the ruby code I came up with:

	class Array
		def group_sequential
			result = []
			group = []
			finish_group = lambda do
				unless group.empty?
					result << group
					group = []
				end
			end

			self.each do |elem|
				if yield elem
					group << elem
				else
					finish_group.call
					result << [elem]
				end
			end
			finish_group.call
			result
		end
	end
	

Things are slightly less noisy, but assignment is subtly awkward in python without using nonlocal scope keyword (only available in python3):

	def group_sequential(predicate, sequence):
		result = []
		group = []
		def finish_group():
			if group:
				result.append(group)
			return []

		for item in sequence:
			if predicate(item):
				group.append(item)
			else:
				group = finish_group()
				result.append([item])
		group = finish_group()
		return result
	

This feels like something that should be doable in a much more concise way than I came up with above. Any ideas? (In either ruby or python)

Update:

My friend Iain has posted a number of interesting solutions over yonder, which got me thinking differently about it (specifically, reminding me of dropwhile and takewhile). I applied python’s itertools to the problem to get this rather satisfactory result in python:

	from itertools import takewhile, tee, dropwhile
	def group_sequential(pred, sequence):
		taker, dropper = tee(iter(sequence))
		while True:
			group = list(takewhile(pred, taker))
			if group: yield group
			yield [dropwhile(pred, dropper).next()]
	

(note: this is a generator which is fine for my purposes - you can always wrap it in a call to list() to force it into an actual list).

The same approach is acceptable when done in ruby, but a bit more verbose because of the need to explicitly check for the end of the sequence, and to collect the results array:

	class Array
		def group_sequential(&pred)
			sequence = self
			results = []
			while true
				group = sequence.take_while &pred
				results << group if group.size > 0
				sequence = sequence.drop_while &pred
				return results if sequence.empty?
				results << [sequence.shift]
			end
		end
	end
	

Update (the second):

While poking around itertools, I managed to miss groupby. I assumed it did the same thing as ruby’s Enumerable#group_by, which is to say not at all what I want (though it’s surely useful at other times). So here is presumably the most concise version I’ll find, for the sake of closure:

	from itertools import groupby
	def group_sequential(pred, sequence):
		return [list(group) for key, group in groupby(sequence, pred)]
	

I had cause to repurpose this immediate feedback formatter to work with the SpecDoc rspec formatter. So here’s a minimal version that just monkey-patches the SpecdocFormatter class to provide immediate feedback. As long as it’s included somewhere before rspec starts running, it should do its thing…

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I’m frequently frustrated with the melbourne public transit system’s mobile offerings. metlink.mobi is probably the easiest way to get on-the-spot timetable information, but it’s pretty awkward to use on touchscreen devices. So metlinkmobi.appspot.com is basically a skin around it, making it more useful on touch devices and also somewhat RESTful (all the URLs should be bookmarkable).

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