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Always interested in offers/projects/new ideas. Eclectic experience in fields like: numerical computing; Python web; Java enterprise; functional languages; GPGPU; SQL databases; etc. Based in Santiago, Chile; telecommute worldwide. CV; email.

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Lepl parser for Python.

Colorless Green.

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SVG experiment.

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Calibration of seismometers.

Data access via web services.

Cache rewrite.

Extending OpenSSH.

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Those little tab things on the side of jet engines; Re: Python's sad, unimaginative Enum; Some explanation; Printing binary trees sideways; About "Python's sad, unimaginative Enum"; Atoms in python; Some good feedback here; Frustration Understood; I agree with you #nt; What would be imaginative?; Re: Enum; this is fucking useless; Enum; Python's sad, unimaginative Enum; Possible Fix; Work, Exhaustion, Vacation; VirtualBox with Centos 6.3 to 6.4, client; Matasano - Programming Lessons Learned; PDF to HTML; Alternate Substitution; Why RSA Works; Trigger; Dreaming of Death; Example: Tracing; Using Coroutines In Protocol Simulations; Python 3.3 Only; Pure Python SHA1 and MD4 Implementations; Ubuntu on VirtualBox; Starting TOR as a service on OpenSuse 12.3; 1001 Albums; Using fail2ban on OpenSuse 12.3; PPPoE on OpenSuse 12.3; Good Article on Unified Physics; It's Police (Carabineros); Linux Software for Listening to and Exploring Music; Android is Pretty Bad; Lucky Number; 3D Printing for Casting; Cover Art for MPDroid; Who'd a thought the French were so bigoted?; PS Input Signal; Small Problem with Roksan K2 Amp; Roksan K2 Amp + ATC SCM7 Speakers; Do What Makes Sense; Re: Arguing About Tests, Still; Arguing About Tests, Still; Images; Good Article on NY Drummers; Related Bug Report; Getting Python 3.3 and Virtualenv Working in OpenSuse 12.3; How I Am; Awesome video about digital audio; The Difference Between Dimensional and Normalized Databases; The rise of the new Chinese bogeyman; Updated Syntax; Very First Steps to C-ORM; The Ideal User Interface For Music Exploration; Can The Republicans Be Saved?; Rate Limiting Calls to EchoNest; Mods to Cache; Comparing UYKFG and UYKFD/E/F; Someone Else is Concerned; EchoNest-based Playlist Generator for MPD; Example Voting Results; A Heavyweight Python Cache; Identifying Artists with EchoNest; Notes on Pregalex / Pregabalina / Lyrica; The Neil Cowley Trio; Drake - Make for Data; A Reliable Python Web Service; Useful Python Date/Time Library?; Need to Sleep, But this is Good; Command Line Set Difference; Little Details...; Linux Command Line Tricks; AutoTools Tutorial; Hangman Tactics; A Tor Proxy Embedded In A Web Page; Tree (Nested Dicts) in Python; Sleeping at Parties; I Know Someone Who Hurts Other People; Light and Tea; Description of the LCS35 Time Capsule Crypto-Puzzle; Re: I can relate to that ...; I can relate to that ...; Re: It's 2012 Why Does My IDE Suck?; My Own Alternative Medicine; Nice explanation of SVM; Why and How Writing Crypto is Hard; Re: It's 2012 Why Does My IDE Suck?; Incremental Regular Expressions; BBC Map Confused at Pole; Social Media: Ground Zero in the Culture War; My Visit to the Psycho Doc; Learning Modern 3D Graphics Programming; Hope you got some crackers to go with the cheese; Re: But how easy would it be ...; But how easy would it be ...; Powerline Freq Fingerprinting of Audio; The Folly of Scientism; Cheese - Because You're Going to Die Anyway

Implementing a Regular Expression Engine

From: "andrew cooke" <andrew@...>

Date: Sun, 22 Mar 2009 20:21:29 -0400 (CLT)

A week or two ago I posted a message here saying I had implemented a
regular expression engine.  I deleted it today...

It would be more correct to say I have been learning about how to
implement a regular expression engine by failing to implement one. 
However, I am making some progress.

My initial take on regular expressions was to treat them as a tree
(basically the parse tree you would expect from their string
representation).  While that wasn't necessarily wrong, it made life a lot
harder than it should have been - it is much easier to model them as
directed graphs.

One translated into graph form, it's pretty easy to generate a
non-deterministic finite automaton that does the appropriate matching. 
That's because it's pretty much the same as the core loop for trampolined
recursive descent parser.  You can even get all the different matches with
back-tracking (technically I am therefore implementing the NFA (with eta
transitions, which are useful to order different parts of the automoaton)
using a PDA, which is more general and so explains the connection to
recursive descent parsing).

That's as far as I have got.  A previous post here gives references on how
to translate the NFA to a DFA (which being deterministic is a lot easier
to "run"; the flip side is that it may have exponentially more states and
there's no way to implement it so that all variations (non greedy matching
etc) are returned).

My aim is to make this NFA a standard LEPL matcher.  The DFA
implementation will be used for lexing.  In the future I'd also like to
see if compiling Any, Literal, Word etc (and combinations with And, Or,
Repeat) to NFA make things faster.

Andrew

http://en.wikipedia.org/wiki/Automata_theory - the table at the bottom is
particularly useful.

Initial DFA Results

From: "andrew cooke" <andrew@...>

Date: Tue, 24 Mar 2009 20:52:27 -0400 (CLT)

This is sweet - it's nice when a piece of code does things you didn't
really expect it to do (I mean, in theory, I can see why it works, but in
practice, the way it solves the problems is almost "intelligent").

Here's an example for the regexp a(bc|b*d):

     a      d
  0 ---> 1 +--> 2* <--+----.
           |b     c/d |    |
           `--> 3 +---'    |
                  |b      d|
                  `--> 4 +-'
                  '      |b
                  |      |
                  `------'

or, as printed (the [...] are the original nfa nodes):

  0 [0]       a:1,
  1 [3, 5, 6] d:2;b:3,
  2 [1, 2]    label,
  3 [4, 5, 6] b:4;[c-d]:2,
  4 [5, 6]    b:4;d:2

Andrew

Original NFA

From: "andrew cooke" <andrew@...>

Date: Tue, 24 Mar 2009 21:11:09 -0400 (CLT)

Just for fun, here's the underlying NFA (with eta/empty transitions). 
This is easier to construct (both by hand and in code)

      a     b      c
  0 ---> 3 +--> 4 ----------+> 1 ---> 2 "label"
           |                |
           |              d |
           `--> 5 +--> 6 ---'
           '      |
           |   b  |
           `------'

0 a:3
1 2
2 label
3 b:4 5
4 c:1
5 b:5 6,
6 d:1

(This is all left to right except for the b* loop from/to 5 at the bottom)

Andrew

Epsilon!

From: "andrew cooke" <andrew@...>

Date: Tue, 24 Mar 2009 21:25:35 -0400 (CLT)

I've been calling my epsilons etas!  Ooops.  Andrew

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