| Andrew Cooke | Contents | Latest | RSS | Twitter | Previous | Next

C[omp]ute

Welcome to my blog, which was once a mailing list of the same name and is still generated by mail. Please reply via the "comment" links.

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.

Personal Projects

Lepl parser for Python.

Colorless Green.

Photography around Santiago.

SVG experiment.

Professional Portfolio

Calibration of seismometers.

Data access via web services.

Cache rewrite.

Extending OpenSSH.

C-ORM: docs, API.

Last 100 entries

Navier Stokes Incomplete; More on Benford; FBI Claimed Vandalism; Architectural Tessellation; Also: Go, Blake's 7; Delusions of Gender (book); Crypto AG DID work with NSA / GCHQ; UNUMS (Universal Number Format); MOOCs (Massive Open Online Courses); Interesting Looking Game; Euler's Theorem for Polynomials; Weeks 3-6; Reddit Comment; Differential Cryptanalysis For Dummies; Japanese Graphic Design; Books To Be Re-Read; And Today I Learned Bugs Need Clear Examples; Factoring a 67 bit prime in your head; Islamic Geometric Art; Useful Julia Backtraces from Tasks; Nothing, however, is lost with less discomfort than that which, when lost, cannot be missed; Article on Didion; Cost of Living by City; British Slavery; Derrida on Metaphor; African SciFi; Traits in Julia; Alternative Japanese Lit; Pulic Key as Address (Snow); Why Information Grows; The Blindness Of The Chilean Elite; Some Victoriagate Links; This Is Why I Left StackOverflow; New TLS Implementation; Maths for Physicists; How I Am 8; 1000 Word Philosophy; Cyberpunk Reading List; Detailed Discussion of Message Dispatch in ParserCombinator Library for Julia; FizzBuzz in Julia w Dependent Types; kokko - Design Shop in Osaka; Summary of Greece, Currently; LLVM and GPUs; See Also; Schoolgirl Groyps (Maths); Japanese Lit; Another Example - Modular Arithmetic; Music from United; Python 2 and 3 compatible alternative.; Read Agatha Christie for the Plot; A Constructive Look at TempleOS; Music Thread w Many Recommendations; Fixed Version; A Useful Julia Macro To Define Equality And Hash; k3b cdrom access, OpenSuse 13.1; Week 2; From outside, the UK looks less than stellar; Huge Fonts in VirtualBox; Keen - Complex Emergencies; The Fallen of World War II; Some Spanish Fiction; Calling C From Fortran 95; Bjork DJ Set; Z3 Example With Python; Week 1; Useful Guide To Starting With IJulia; UK Election + Media; Review: Reinventing Organizations; Inline Assembly With Julia / LLVM; Against the definition of types; Dumb Crypto Paper; The Search For Quasi-Periodicity...; Is There An Alternative To Processing?; CARDIAC (CARDboard Illustrative Aid to Computation); The Bolivian Case Against Chile At The Hague; Clear, Cogent Economic Arguments For Immigration; A Program To Say If I Am Working; Decent Cards For Ill People; New Photo; Luksic And Barrick Gold; President Bachelet's Speech; Baltimore Primer; libxml2 Parsing Stream; configure.ac Recipe For Library Path; The Davalos Affair For Idiots; Not The Onion: Google Fireside Chat w Kissinger; Bicycle Wheels, Inertia, and Energy; Another Tax Fraud; Google's Borg; A Verion That Redirects To Local HTTP Server; Spanish Accents For Idiots; Aluminium Cans; Advice on Spray Painting; Female View of Online Chat From a Male; UX Reading List; S4 Subgroups - Geometric Interpretation; Fucking Email; The SQM Affair For Idiots; Using Kolmogorov Complexity; Oblique Strategies in bash; Curses Tools

© 2006-2015 Andrew Cooke (site) / post authors (content).

Interpreter for Python Regexps

From: andrew cooke <andrew@...>

Date: Thu, 27 May 2010 08:16:19 -0400

I have been working on a regular expression package for Python - a pure Python
implementation that will, eventually, be integrated into Lepl.  So far parsing
works (I can now parse almost all of Python's regular expression syntax) and I
have just got a very basic interpreter (effectively NFA) based engine running
some basic matches.  The following tests pass:

class VisitorTest(TestCase):
    
    def test_string(self):
        assert Visitor(Unicode(), parse('abc'), 'abc')
        assert Visitor(Unicode(), parse('abc'), 'abcd')
        assert not Visitor(Unicode(), parse('abc'), 'ab')
        
    def test_dot(self):
        assert Visitor(Unicode(), parse('a.c'), 'abc')
        assert Visitor(Unicode(), parse('...'), 'abcd')
        assert not Visitor(Unicode(), parse('...'), 'ab')

As I hoped, the parsing has been by far the hardest part.  Actually writing an
implementation given the parsed graph and visitor interfaces is pretty easy.

The parser, as implied above, generates a directed graph of nodes that reflect
the different operations supported.  This could then be "compiled" by an
implementation or simply used directly.  For direct use it supports a basic
visitor pattern, where each node implements .visit(visitor, state) and then
"calls back" on the visitor.  So the visitor callback methods are equivalent
to the different bytecodes that would be used in compilation:

class Visitor(object):
    def string(self, next, text, state=None):
    def character(self, next, state=None):
    def start_group(self, next, number, state=None):
    def end_group(self, next, number, state=None):
    def group_reference(self, next, number, state=None):
    def conditional(self, next, number, state=None):
    def split(self, next, state=None):
    def match(self, state=None):
    def dot(self, next, multiline, state=None):
    def start_of_line(self, next, multiline, state=None):
    def end_of_line(self, next, multiline, state=None):
    def lookahead(self, next, sense, forwards, state=None):
    def repeat(self, next, begin, end, state=None):
    def word_boundary(self, next, inverted, state=None):
    def digit(self, next, inverted, state=None):
    def space(self, next, inverted, state=None):
    def word(self, next, inverted, state=None):

(Note that "repeat" is replaced by explicit expansion in the parser if the
appropriate options are set; also, expansion of character classes is handled
by an "alphabet" that is not otherwise explicit here).

Andrew

Comment on this post