| 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

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; Markov Chain Monte Carlo Without all the Bullshit; Email Para Matias Godoy Mercado; The Penta Affair For Idiots; Example Code To Create numpy Array in C; Good Article on Bias in Graphic Design (NYTimes); Do You Backup github?; Data Mining Books; SimpleDateFormat should be synchronized; British Words; Chinese Govt Intercepts External Web To DDOS github; Numbering Permutations; Teenage Engineering - Low Price Synths; GCHQ Can Do Whatever It Wants; Dublinesque; A Cryptographic SAT Solver; Security Challenges; Word Lists for Crosswords; 3D Printing and Speaker Design; Searchable Snowden Archive; XCode Backdoored; Derived Apps Have Malware (CIA); Rowhammer - Hacking Software Via Hardware (DRAM) Bugs; Immutable SQL Database (Kinda); Tor GPS Tracker; That PyCon Dongle Mess...; ASCII Fluid Dynamics; Brandalism; Table of Shifter, Cassette and Derailleur Compatability; Lenovo Demonstrates How Bad HTTPS Is; Telegraph Owned by HSBC; Smaptop - Sunrise (Music); Equation Group (NSA); UK Torture in NI; And - A Natural Extension To Regexps; This Is The Future Of Religion; The Shazam (Music Matching) Algorithm; Tributes To Lesbian Community From AIDS Survivors; Nice Rust Summary; List of Good Fiction Books; Constructing JSON From Postgres (Part 2); Constructing JSON From Postgres (Part 1); Postgres in Docker; Why Poor Places Are More Diverse; Smart Writing on Graceland; Satire in France; Free Speech in France; MTB Cornering - Where Should We Point Our Thrusters?; Secure Secure Shell; Java Generics over Primitives; 2014 (Charlie Brooker); How I am 7; Neural Nets Applied to Go; Programming, Business, Social Contracts; Distributed Systems for Fun and Profit; XML and Scheme; Internet Radio Stations (Curated List); Solid Data About Placebos; Half of Americans Think Climate Change Is a Sign of the Apocalypse; Saturday Surf Sessions With Juvenile Delinquents; Ssh, tty, stdout and stderr; Feathers falling in a vacuum; Santiago 30m Bike Route; Mapa de Ciclovias en Santiago; How Unreliable is UDP?; SE Santiago 20m Bike Route; Cameron's Rap; Configuring libxml with Eclipse; Reducing Combinatorial Complexity With Occam - AI; Sentidos Comunes (Chilean Online Magazine); Hilary Mantel: The Assassination of Margaret Thatcher - August 6th 1983; NSA Interceptng Gmail During Delivery; General IIR Filters; What's happening with Scala?; Interesting (But Largely Illegible) Typeface; Retiring Essentialism; Poorest in UK, Poorest in N Europe; I Want To Be A Redneck!; Reverse Racism; The Lost Art Of Nomography; IBM Data Center (Photo); Interesting Account Of Gamma Hack; The Most Interesting Audiophile In The World; How did the first world war actually end?; Ky - Restaurant Santiago; The Black Dork Lives!; The UN Requires Unaninmous Decisions; LPIR - Steganography in Practice

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

Good Hacks, Bad Hacks - Experiences with DSLs in Java

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

Date: Wed, 28 Jun 2006 10:05:29 -0400 (CLT)

Some simple observations / notes / reflections.

Implementing a system to load a set of database tables with data, I used a
DSL to specify the relationship between the tables (key relations) and the
data source.

I separated the language into two stages.  In the first stage you could
only define types (table structures).  The second stage extended the
first, allowing the full set of features.

That seemed a bit odd, and the implementation was rather ugly, but still
turned out to be a good idea.  The goodneess came from the possibility of
generating the first stage from the database (via postgres's "meta"
tables).

Having this information as a simple AST allowed us to combine (incomplete)
database meta-information with extra user-added text (by merging ASTs). 
That may not be clear - I am talking about the first stage only.  We could
both generate the description from the database and via text files.  The
two were complementary.

Extra checks in the second stage guaranteed that all referenced tables
were fully defined (ie non "not null" values were missing).  This check
cannot be made on the first stage because that includes all tables (even
those nto populated by this particular invocation).  In otehr words, the
first stage defines the database; the second stage selects some tables
from that for populating.

However, there were also some bad points.  First, what is the relationship
(implementation-wise) between the two stages?  I had them sharing common
base classes and copying data across (so when a table is references in the
second stage for the first time, all data from the first stage is copied
across).

It would have been better for the second stage to include a reference to
the first stage ("has a", rather than a bastardised "is a").

Another bad point was the syntax.  I argued that I didn't have time to
write a parser, and came up with what seemed like an elegant hack -
http://www.acooke.org/cute/UsefulJava0.html - which gave me the parse tree
directly (note that the language is declarative, so order of statements is
unimportant).

However, this has confused users, since the lhs of the syntax is a set of
arbitrary names to label branches in the AST and therefore has no direct
connection between the two stages.

At the same time, in another part of the system, I wrote (in less time
than the hack above, I suspect) a very simple "lazy scheme" (without,
currently, function defn / lambda abstraction, continuations, macros, or
most standard functions) (laziness allows "everything" to be a function). 
We could have used that here.

One other regret - I should have been clearer about the DSL approach. 
I've written enough language-related code to have absorbed many of the
patterns, which led to using them without a clear high-level description
(I had a design/sketch for how things would work, but not a simple,
unifying "vision").  Just thinking of the system "as a language" would
have helped clarify things, I believe.  Certainly it would have made it
easier to explain to others later (the current system, with no real
language to speak of - just this "parse trees as properties" - looks like
a monolith with arbitrarily complex configuration values, rather than an
interpreter).

Andrew

Comment on this post