Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!wuarchive!usc!apple!amdahl!key!tomf
From: tomf@key.COM (Tom Faulhaber)
Newsgroups: comp.lang.lisp
Subject: Re: Re: extension languages can be darn small, yet still powerfull
Message-ID: <2083@key.COM>
Date: 29 Aug 90 23:59:47 GMT
References: <1990Aug26.205018.18067@cbnewsc.att.com> <1350028@otter.hpl.hp.com>
Reply-To: tom@marble.COM (Tom Faulhaber)
Organization: Marble Associates
Lines: 45

In article <1350028@otter.hpl.hp.com> sfk@otter.hpl.hp.com (Steve Knight) writes:
>It is quite easy to imagine a programming language with (say) an Algol-like
>syntax in which the parse tree is available as a standard data-structure.
>Extending the language has several solutions.  The elegant solution might
>be to create new grammar rules with associated rewrite actions.

Actually a language that I think meets your criteria was developed at
Harvard in the early 70s.  It was called EL1 (Extensible Language 1) and
it was like Algol on the outside and like Lisp on the inside.  A system
called PDS (Program Development System) was built around it which
supplied the capabilty to write rewrite rules.  These rules were very
similar to macros in modern Lisps, but with an Algol-like syntax.  The
approach commonly used could be described as somewhat object-oriented in
that programmers would develop interfaces to their datatypes at a high
level without concern for the underlying impelmentation and then specify
the rewrite rules to translate the high-level primtives into actual
code.

Interfaces included not only functions but operators (any symbol could
be an operator) and iterators (and any syntactic sugar you could think
of to make the job easier).

EL1 had many of the shortcomings of the Lisps of its day, including
totally dynamic scoping, but it fostered an interesting approach to
programming.

EL1 was taught to upper-level undergraduates in a course called AM113
throughout the seventies and into the early eighties.  Some ex-students
still haven't fully recovered :-).

I don't have the references on EL1 handy, but the primary source was Ben
Wegbreit's Ph.D. thesis at Harvard (around 1974, I think).  Others who
wrote about aspects of the system were Tom Cheatham (the Prof behind it
all), Judy Townley, and Glenn Holloway.

Send me mail if you want more info and I'll try to dig it out.

Tom


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Thomas A. Faulhaber, Jr.	tom@marble.com
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