Tom Moertel's Blog

PXSL Tools now on Hackage and GitHub

Posted by Tom Moertel Mon, 25 Aug 2008 02:56:00 GMT

I finally got around to releasing PXSL Tools on Hackage. The package contains pxslcc, a preprocessor that converts Parsimonious XML Shorthand Language into XML, and supporting documentation.

If you want to hack on the Haskell sources, I’ve put the project on GitHub, too. See the pxsl-tools project page to browse the code, or just clone the repo and hack away:

$ git clone git://github.com/tmoertel/pxsl-tools.git

Tags git, haskell, pxsl
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Thinking algebraically: a functional-programming dividend that pays during your imperative-programming day job

Posted by Tom Moertel Thu, 21 Aug 2008 01:50:00 GMT

Although at work I code mostly in Python – a language from which lambda and map were nearly removed – I still find that functional-programming experience has its benefits. One of the “functional-programming dividends” I notice most often is insight gained from considering problems from an algebraic perspective.

Recently, for example, I had a small parsing problem. I had to write code that, given a simple grammar specification as input, emits a regular expression that matches the language generated by the grammar.

Here’s a simplified version of the problem. A grammar specification is limited to a series of one or more atoms. For example, “a b c” represents the atom “a”, followed by the atom “b”, followed by the atom “c”. To generate the grammar, the series of atoms is interpreted such that each atom (except the last) generates a production rule of the following form:

atom_rule ::=
  <the literal atom> (SPACE <the next rule> | NOTHING)

(SPACE represents literal white space and NOTHING represents an empty string.) The grammar as a whole is rooted in the first atom’s rule.

Thus the specification “a b c” represents the following grammar:

grammar ::= a_rule
a_rule  ::= "a" (SPACE b_rule | NOTHING)
b_rule  ::= "b" (SPACE c_rule | NOTHING)
c_rule  ::= "c" 

Note that the final atom’s production matches only the literal atom itself: it has no following rule on which to chain.

The grammar, in turn, generates the following language:

a
a b
a b c

Thus, given the grammar specification “a b c”, my code had to produce a regular expression that would match “a”, “a b”, or “a b c”.

At this point, please stop for a moment and think about this little programming exercise. Do any solutions leap to mind? How would you approach the problem? Form your opinions now, because I’m going to ask you about them later. (If you’re feeling especially caffeinated, try coding a solution before reading on.)

Posted in functional programming
Tags folds, fp, haskell, python
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Fun stuff: Video of Type B Erie steam shovel in action!

Posted by Tom Moertel Sun, 10 Aug 2008 18:12:00 GMT

As an update to my previous post on the 2008 convention of the Historical Construction Equipment Association, I have posted an action-packed video of a Type-B Erie steam-powered shovel! Wait until you see this old beast belch steam and smoke and you hear it chug, clank, and huff and puff – it’s like stepping back in time. And it’s definately fun stuff!

I took this footage on 8 August 2008 in Brownsville, Pennsylvania. (I also have footage of other equipment – dozers, draglines, trucks, shovels, and more. Let me know if you’re interested, and I’ll upload those, too.)

Posted in fun stuff
Tags fun_stuff, hcea, hcea2008, steam_shovel, video
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Fun stuff: Historical Construction Equipment Association's 2008 convention

Posted by Tom Moertel Sun, 10 Aug 2008 00:23:00 GMT

Today, my dad and I went to the 2008 annual convention of the Historical Construction Equipment Association. We were impressed with the quantity and quality of the machinery on active display: steam shovels, dozers, graders, crawlers, scrapers, cranes, steamrollers, and a bunch of other old but well-maintained construction equipment. I’m talking dozens of massive machines – not just sitting there, but working!

This year’s convention is in Brownsville, Pennsylvania and runs through August 10, 2008. If you are within driving distance and think smoke-belching, earth-shaking construction equipment is fun stuff, don’t miss it. There’s still time to go.

If you can’t make it, I took some photos for you. Not quite the real thing, but better than nothing.

Posted in fun stuff
Tags fun_stuff, hcea, hcea2008
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