Path: utzoo!utgpu!watserv1!ria!ria.ccs.uwo.ca!yukngo
From: yukngo@obelix.gaul.csd.uwo.ca (Cheung Yukngo)
Newsgroups: comp.lang.lisp
Subject: Re: Lisp shells for Unix (was: Extensible languages....)
Message-ID: <YUKNGO.90Aug30165843@obelix.gaul.csd.uwo.ca>
Date: 30 Aug 90 15:58:43 GMT
References: <13198@hydra.gatech.EDU>
Sender: news@ria.ccs.uwo.ca
Organization: Dept. of C.S., University of Western Ontario
Lines: 53
In-reply-to: ken@dali.gatech.edu's message of 30 Aug 90 22:10:32 GMT

Last year, I implemented a Lisp-based shell using the ELI lisp that
comes with the Andrew toolkit from CMU. I got to the stage that pipes,
redirections, job control, etc can be done. I did the implementation
to learn how shells do the things they do. I did not debug it to the
stage that it could replace /bin/csh or /bin/sh, not to mention bash
or tcsh. I did not read the papers discussing Lisp shells (I did not
know of their existance). I'd appreciate it if somebosy could give the
references. I did encounter quite a few interesting problems with my
implementation.

I don't think I should bore you with all the problems I encountered.
Here is a few more interesting ones (in my opinion):

1. How should pipes be specified? 

   (pipe (cat prog.c) (egrep "here") (> "matches")) ?

   Think how the lisp interpreter should execute this thing. After you
   evaluate the arguments, then you do the pipe? Don't evaluate the
   arguments, and let each builtin function worries about the
   evaluation of the arguments (like is done in ELI)? How to mix
   outputs from, say 'car' and output from 'cat'?

2. What exactly are the programs in your search PATH? Are they in the
   same class as 'car' and 'cdr'? Should we have:

   (cat "a.c")
      or
   (! 'cat "a.c") ?

   Should the PATH variable be continued?

3. What status should be given to the output of a program? Is it a
   return value? Part of a return value? Side effects and nothing
   else?

4. With the use of lisp, the traditional one line command buffer for
   executing commands can be discarded (since most lisp program is not
   going to be one line or should be typed on the same line). What
   should replace it? A screen for issuing commands and one screen for
   executing them? One window for the commands and one window for the
   output, in a window system? Think about doing terminal handling and
   command editing as in tcsh or bash. Seems like we need a full
   editor.

There are a lot of good things to say about a shell based in Lisp. I
like the idea. The problems are interesting and challenging.
Unfortunately, I have not met a single graduate student here that was
interested enough to actually tried the shell. Pretty tough to tell
them that parentheses are good for them :-)

Khun Yee