I've been reading the ``Types and Programming Languages'' ( TAPL ) book bought from Amazon.com and I've been playing with functional languages. The TAPL book uses OCaml for sample interpreter implementations and I started by learning OCaml in the hope of using it in $work. Sadly OCaml's json-static and dbd-pg/postgresql libraries gave me too much pain to install and OCaml's restricted type system made me rather unhappy. So I turned to Haskell . Well, I should have said ``returned'' ;)

The syntax of Haskell is even cleaner than OCaml and its type system is much more powerful. I quickly got familiar with Parsec and monads in general by going through the famous tutorial ``Write yourself a scheme in 48 hours''. Furthermore, the TAPL book's introduction to the lambda-calculus language helped me understand the functional programming paradigms ubiquitous in Haskell.

Great. Within just a few days, I came up with a working minisql parser for OpenResty which parses simple SQL select statements using Parsec. Building combinator parsers is really enjoyable. The whole parser is composed by several smaller ones which are in turn built upon even smaller ones and so on. Each combinator parser can also take parameters if necessary because they're essentially Haskell functions after all. The ability to do infinite look-aheads in Parsec gives me a lot of freedom to disambiguate my grammar without much hassles. Moreover, Parsec does not backtrack by default, so the parsing speed is still pretty good. Compared to the old minisql parser written in Perl (via the Parse::Yapp module), the Haskell version is at least 1 order of magnitude faster. Besides, the source of the Haskell one is also shorter and cleaner.

In the next few days, I happily mudded with the AST constructed by the parser and built four emitters atop it. These emitters are required by the new version of the OpenResty View API.

I successfully used Perl along with its modules Test::Base and IPC::Run3 to build a test scaffold for my Haskell compiler. The test suite is completely declarative and extensible. Surprisingly, I could still use the Haskell Program Coverage ( hpc ) toolchain to obtain a pretty HTML report for the code coverage of the whole test suite driven by Perl. So glad to have such a Devel::Cover equivalent on the Haskell land!

The source repository for my Haskell version of minisql compiler is located at

http://svn.openfoundry.org/openapi/trunk/haskell/

In the following journal or two I'd like to share the experience of optimizing my minisql compiler and making it several times faster.

Here's the video for my D2 talk about OpenResty (well, it's mostly a Chinese talk :P):

  Part 1: http://www.tudou.com/programs/view/3Tn42pPk0aU/
  Part 2: http://www.tudou.com/programs/view/Q5stEI3TSIc/
  Part 3: http://www.tudou.com/programs/view/peznAkBaJHA/
  Part 4: http://vimeo.com/1013264

Videos for other speakers can be found here:

http://www.tudou.com/home/user_programs.php?userID=25459589&page=1

Enjoy!