Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!tut.cis.ohio-state.edu!snorkelwacker!bloom-beacon!ZURICH.AI.MIT.EDU!jinx
From: jinx@ZURICH.AI.MIT.EDU ("Guillermo J. Rozas")
Newsgroups: comp.lang.scheme
Subject: Bug in MIT-Scheme
Message-ID: <9003221201.AA11816@zurich.ai.mit.edu>
Date: 22 Mar 90 12:01:42 GMT
References: <2063@laura.UUCP>
Sender: daemon@athena.mit.edu (Mr Background)
Reply-To: jinx@zurich.ai.mit.edu
Organization: The Internet
Lines: 60


   Date: 21 Mar 90 13:46:55 GMT
   From: Holger Muenx <mcsun!unido!laura!heike.informatik.uni-dortmund.de!muenx@uunet.uu.net>

   I think I found a small bug in MIT-Scheme V7.0. Look at the following
   transcript:

	   1 ]=> (string->symbol "loadConst")

	   ;Value: loadConst

   The resulting symbol consists of upcase und lowercase letters. It's a bit
   disturbing if you look at these lines:

	   1 ]=> (eq? (string->symbol "loadConst") 'loadConst)

	   ;Value: ()

	   1 ]=> (eq? (string->symbol "loadConst") 'loadconst)

	   ;Value: ()

   Any idea?

						      -Holger

The R3RS report, in the section for symbols (sectin 6.4) reads:

"The string->symbol procedure, however, can create symbols for which
this write/read invariance may not hold because their names contain
special characters of letters in the non-standard case."

Given that MIT Scheme uses lower case as the standard case, the print
name for symbol 'loadConst is "loadconst", and (string->symbol
"loadConst") returns a symbol whose print name is "loadConst", so they
are clearly distinguishable.

In other words, there is no way to type the symbol whose print name
is "loadConst", since READ canonicalizes 'loadConst to 'loadconst and
(eq? 'loadConst 'loadconst) -> #t

It would be nice if the reports included a procedure called INTERN (or
something like that) which when given a string, would canonicalize it
(transform it to the standard case) and then use string->symbol on it.
The report does not have such functionality, although it can be
defined portably (using some inessential procedures), albeit somewhat
awkwardly:

(define intern
  (let ((standard-is-lower?
	 (string=? "a" (symbol->string 'A))))
    (lambda (string)
      (string->symbol
       (list->string
	(map (if standard-is-lower?
		 char-downcase
		 char-upcase)
	     (string->list string)))))))

MIT Scheme (>= 7.0) has INTERN pre-defined.