Path: utzoo!attcan!uunet!husc6!uwvax!tank!uxc!uxc.cso.uiuc.edu!m.cs.uiuc.edu!wsmith
From: wsmith@m.cs.uiuc.edu
Newsgroups: comp.software-eng
Subject: Re: Structured Editor vs. Text Editor
Message-ID: <39400004@m.cs.uiuc.edu>
Date: 4 Nov 88 20:40:00 GMT
References: <3385@pt.cs.cmu.edu>
Lines: 59
Nf-ID: #R:pt.cs.cmu.edu:3385:m.cs.uiuc.edu:39400004:000:3212
Nf-From: m.cs.uiuc.edu!wsmith    Nov  4 14:40:00 1988


I will try to briefly respond to the points raised by Johnny Martin.

First, one should not make generalizations about an editor based on such a
short description.  Leif is a complex program that is more than a "background 
syntax checker."  It contains an incremental parser that efficiently 
maintains a parse tree that may be consulted to visualize the syntactic 
structure of the program as well as locate errors.  Leif is definitely not 
slow.

Secondly, there are other ways of categorizing language oriented
editors.  Martin's categorization begs the question by implying that "True
SDE's have great power" and thus must abandon text editing commands to provide 
this power.  Leif does not yet provide all of the transformational 
power of the ideal philosopher's stone SDE but it provides enough power to
be worthwhile.

While emphasizing that a nice user interface is "a godsend," he assumes that 
text editing does not fit in such a user interface.  Consider Richard Waters 
article "Program Editors Should not Abandon Text Commands."  Syntax directed 
editing is possible within a framework of textual editing and Leif proves 
that.  The transformation and holophrasting capabilities espoused by Martin 
are possible within the Leif framework although they have not been 
implemented yet.  I believe researchers at Berkeley are also independently 
developing an editor with similar capabilities to Leif.

Transformational commands are valuable, but is it possible to proved a complete
set of such commands?  Many transformations should be based on semantic 
information which may be unavailable because of undecidability of understanding
some aspects of programs.

Martin implies that a programmer only wants to use a language oriented editor
on a fixed, standardized language.  In my research, Leif demonstrates that there
is a demand for easily constructed language oriented editors. In Leif, it 
takes only a few hours to create an useful editor once a lexical analyzer and 
LALR grammar have been written.  The problem of creating a useful set of 
transformations is difficult and time consuming.  Similarly, writing emacs 
lisp code to edit in a new language-sensitive mode is non-trivial.

By quickly developing an editor for a special purpose language, the quality
of the language may be improved through an iterative design process.  This
same design process may be used to teach compiler design techniques.
Leif allows many different languages to be edited with no modifications to
the user interface.

The original question that started this discussion demonstrates that the 
design of language oriented editors still pose several research questions.  
The foremost research issue is the user interface.  Leif provides a user 
interface that is radically different that that provided by Xinotech's 
Program Composer that Martin champions.

Finally, evidence that language oriented editors (or syntax directed editors)
are not a solved problem is that they are not widespread and they have only
a limited user community.  Research should continue to improve the tools
available to programmers beyond the limited editing techniques available now.

Bill Smith
wsmith@cs.uiuc.edu
uiucdcs!wsmith