| 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

Weird Finite / Infinite Result; Your diamond is a beaten up mess; Maths Books; Good Bike Route from Providencia / Las Condes to Panul\; Iain Pears (Author of Complex Plots); Plum Jam; Excellent; More Recently; For a moment I forgot StackOverflow sucked; A Few Weeks On...; Chilean Book Recommendations; How To Write Shared Libraries; Jenny Erpenbeck (Author); Dijkstra, Coins, Tables; Python libraries error on OpenSuse; Deserving Trump; And Smugness; McCloskey Economics Trilogy; cmocka - Mocks for C; Concept Creep (Americans); Futhark - OpenCL Language; Moved / Gone; Fan and USB issues; Burgers in Santiago; The Origin of Icosahedral Symmetry in Viruses; autoenum on PyPI; Jars Explains; Tomato Chutney v3; REST; US Elections and Gender: 24 Point Swing; PPPoE on OpenSuse Leap 42.1; SuperMicro X10SDV-TLN4F/F with Opensuse Leap 42.1; Big Data AI Could Be Very Bad Indeed....; Cornering; Postcapitalism (Paul Mason); Black Science Fiction; Git is not a CDN; Mining of Massive Data Sets; Rachel Kaadzi Ghansah; How great republics meet their end; Raspberry, Strawberry and Banana Jam; Interesting Dead Areas of Math; Later Taste; For Sale; Death By Bean; It's Good!; Tomato Chutney v2; Time ATAC MX 2 Pedals - First Impressions; Online Chilean Crafts; Intellectual Variety; Taste + Texture; Time Invariance and Gauge Symmetry; Jodorowsky; Tomato Chutney; Analysis of Support for Trump; Indian SF; TP-Link TL-WR841N DNS TCP Bug; TP-Link TL-WR841N as Wireless Bridge; Sending Email On Time; Maybe run a command; Sterile Neutrinos; Strawberry and Banana Jam; The Best Of All Possible Worlds; Kenzaburo Oe: The Changeling; Peach Jam; Taste Test; Strawberry and Raspberry Jam; flac to mp3 on OpenSuse 42.1; Also, Sebald; Kenzaburo Oe Interview; Otake (Kitani Minoru) move Black 121; Is free speech in British universities under threat?; I am actually good at computers; Was This Mansplaining?; WebFaction / LetsEncrypt / General Disappointment; Sensible Philosophy of Science; George Ellis; Misplaced Intuition and Online Communities; More Reading About Japan; Visibilty / Public Comments / Domestic Violence; Ferias de Santiago; More (Clearly Deliberate); Deleted Obit Post; And then a 50 yo male posts this...; We Have Both Kinds Of Contributors; Free Springer Books; Books on Religion; Books on Linguistics; Palestinan Electronica; Books In Anthropology; Taylor Expansions of Spacetime; Info on Juniper; Efficient Stream Processing; The Moral Character of Crypto; Hearing Aid Info; Small Success With Go!; Re: Quick message - This link is broken; Adding Reverb To The Echo Chamber; Sox Audio Tools; Would This Have Been OK?; Honesty only important economically before institutions develop

© 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