Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!think.com!spool.mu.edu!munnari.oz.au!bruce!goanna!ok
From: ok@goanna.cs.rmit.oz.au (Richard A. O'Keefe)
Newsgroups: comp.lang.prolog
Subject: Re: better than 4-port debugger
Message-ID: <6477@goanna.cs.rmit.oz.au>
Date: 24 Jun 91 09:17:32 GMT
Article-I.D.: goanna.6477
References: <1793@usage.csd.unsw.oz.au>
Organization: Comp Sci, RMIT, Melbourne, Australia
Lines: 31

In article <1793@usage.csd.unsw.oz.au>, jim@hydra.maths.unsw.oz.au writes:
> IMHO, four-port debugging may be fine as an underlying model,
> but is bad as a view of that model. recently, i was doing some
> partial evaluation work and the strutures i was generating filled
> several lines on my 4-port debugger.

That is *precisely* what the print/1 and portray/1 predicates were
invented for.  The (tty interface to) the four-port debugger *must*
call print/1 to display the goals.  You get to define portray/1 to
do whatever level of abbreviation you like.  When I say that print/1
and portray/1 were invented for this, I am writing the literal
truth.  Chris Mellish was working on a program written in DEC-10
Prolog where the goals (even when acyclic) tended to take up a whole
screen.  print/1 and portray/1 were added so that he could abbreviate
the output.  The 'w' command and its relatives in the tty interface
to the 4-port debugger let you over-ride that.

> what i would have prefered
> is a debugger ala Smalltalk where the call history is on a
> click and point list in a window and clicking on item in that
> list pops up another window with all the arguments listed in another
> list. clicking on any one argument would print it to a third window.

> sound tricky, right?
No.
I'm glad that there is a tty interface to some Prolog debuggers,
because I'm using a 24x80 terminal here...  That's not to say that
there shouldn't be additional interfaces.  (

-- 
I agree with Jim Giles about many of the deficiencies of present UNIX.