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From: markf@zurich.ai.mit.edu (Mark Friedman)
Newsgroups: comp.lang.scheme
Subject: Re: function tracing in Scheme
Message-ID: <MARKF.91Apr26151741@montreux.ai.mit.edu>
Date: 26 Apr 91 19:17:41 GMT
References: <JAFFER.91Apr26120238@kleph.ai.mit.edu>
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In-reply-to: jaffer@zurich.ai.mit.edu's message of 26 Apr 91 16:02:38 GMT

In article <JAFFER.91Apr26120238@kleph.ai.mit.edu> jaffer@zurich.ai.mit.edu (Aubrey Jaffer) writes:

   Here is code for tracing functions which should work in any scheme.
   If you have macros on you system you can add some syntactic sugar and
   finish the job.  And yes, it can trace itself.  And no, it doesn't get
   screwed up if you trace functions it uses.

   ;;;; Utility functions for debugging in Scheme.

   ;;; to TRACE type
   ;;; (set! <symbol> (tracef <symbol>)) or
   ;;; (set! <symbol> (tracef <symbol> '<symbol>)) or
   ;;; (define <symbol> (tracef <function>)) or
   ;;; (define <symbol> (tracef <function> '<symbol>))

   ;;; to UNTRACE type
   ;;; (set! <symbol> (untracef <symbol>))

   [code for trace and untrace omitted]

This is all well and good, but only useful for procedures that are
referenced by name (and it only traces them where they are referenced
by that name, and you lose eq-ness for traced procedures). You need
some hackery in the interpreter and/or compiler to make tracing work
for arbitrary procedures.

   ;;; TRACEF REALLY NEEDS A `PRINT ANYTHING ON ONE LINE' ROUTINE.  DOES
   ;;; SOMEONE CARE TO WRITE IT?

Unless I misunderstand what you mean I think that the following will
do it.

(define (display-anything-on-one-line . things)
  (if (not (null? things))
      (let loop ((things things))
	(if (null? things)
	    (newline)
	    (begin
	      (display (car things))
	      (loop (cdr things)))))))

-Mark
--

Mark Friedman
MIT Artificial Intelligence Lab
545 Technology Sq.
Cambridge, Ma. 02139

markf@zurich.ai.mit.edu