I remembered that test language that defined a lot of new
keywords-as-symbols for testing, though not its author. I’d love to do
that here, but I don’t (yet?) have approval to use Ruby as the base
language for the test harness (I do have it in there as a tool for
as-needed use, though, and have written a few tools for the harness with
it). I skipped most of the native-XML thread here, so sorry for the
duplication.
Al
···
-----Original Message-----
From: James Britt [mailto:jamesUNDERBARb@seemyemail.com]
Sent: Tuesday, October 21, 2003 5:40 PM
To: ruby-talk ML
Subject: Re: weird(?) thought about programming languages
Albert Chou wrote:
This thought isn’t necessarily about Ruby specifically, though the
occasional wish expressed here that Ruby have Lisp-like macros added
to
it resonates with it.I’ve been reading Paul Graham’s On Lisp to finally learn what all
this
talk of Lisp macros is about, and I’ve read enough (I’m into chapter
15
so far) to understand a lot of it, generally speaking.
I tried reading that, but after about three or four chapters I decided I
didn’t know enough Lisp to follow along. 
But I was motivated by the same reason, to better understand macros.
I spent some
time trying to understand how it might be possible to use macros to
give
Lisp (or Scheme) a syntax that’s easier for me to read (for instance,
I
find most of the function names I’ve encountered in Common Lisp to be
pretty incomprehensible). I even came across a USENET posting from
about 1991 from a guy who had done that with Scheme, but I couldn’t
find
any more references or a way to contact him. Further searches of the
Web turned up another discussion about making Scheme need fewer
parentheses that finally taught me what I think is a core lesson about
language syntax: it’s difficult, if not impossible, to change the
punctuation of a programming language using its own mechanisms. By
punctuation I mean how tokens are delimited/defined.
There was some similar discussion here about implementing a syntax in
Ruby that would allow one to manipulate XML using near-literal XPath
syntax (along the lines of ECMAScript and E4X).
The discussion about making a less-parenthesized version of Scheme
concluded that you’d have to write a special-purpose reader (basically
parser, IIRC) to accomplish the task. Thus you can write as highly
abstracted and domain-specific a language as you like on top of
Lisp/Scheme, as long as you adhere to the way these parent languages
uses parentheses, whitespace, and alphanumeric characters to define
language tokens. Adding words (and even language constructs, in a
language that has macros) to a language’s vocabulary is easy, but
redefining how to define words is impossible without stepping outside
the language. Of course, you could write a parser for your extended
language in the language you’re extending, but my point is there’s no
way to make a parser for the original language work with the extended
language if you violate the parent language’s punctuation rules.
I believe Phil Thomson has done some work creating a meta-language in
Ruby to allow QA/testers to write and run scripts that are, techincally,
Ruby, but do not require any profound understanding of Ruby’s nuts and
bolts. (And Ruby itself is a meta-language on top of C.)
That sort of thing, as well as Graham’s On Lisp macro stuff, is along
the lines of “build a language, not an application.”[0]
James
[0] http://www.pragmaticprogrammer.com/ppllc/papers/1998_03.html