Saturday, April 19, 2008

Using JSON for communicating between Ruby and Lisp or Scheme

JSON is very much lighter weight than XML and is meeting a need for easily calling some Scheme code from a Ruby program. The Scheme code I am using is old, I wrote it years ago to extract entities from plain text. Since the Scheme program starts very quickly, I am able to simply start a Scheme interpreter as a separate process using back quotes to capture any output to stdout in a Ruby string variable:
require 'json'
s = `gsi extraction.scm -e '(get-proper-names "President Bush moved to South America.")'`
# parse JSON text...
Here I am using Gambit-C Scheme interpretively. It is very easy to write any structured data in JSON format in the Scheme (or Lisp) code and parse it on the Ruby side. It is also easy to speed things up and compile my program:
gsc -c extraction.scm
gsc -link extraction.c
gcc -o extraction extraction.c extraction_.c -lgambc -I/Library/Gambit-C/current/include/ -L/Library/Gambit-C/current/lib/
which both makes the program faster and reduces the startup time down to a few milliseconds. Since the extraction program starts very quickly, this solution is good enough. However, I have been looking at an alternative idea in case I ever need to use a Lisp or Scheme program that has a long startup time. I have not done this yet, but here are my ideas for Gambit-C Scheme:
  • Write a C wrapper for the Scheme (a good reference) to create a Ruby callable class whose initialization method performs the long running initialization for the Scheme library
  • Wrap the Scheme side library according to this reference
This looks easy enough, but getting memory allocation and deallocation correct might be difficult. For now, I am calling my old Scheme code from Ruby the easy way :-)

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