This is the mail archive of the guile@sourceware.cygnus.com mailing list for the Guile project.

Index Nav:	[Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav:	[Date Prev] [Date Next]	[Thread Prev] [Thread Next]

Re: another nit.

To: Dirk Herrmann <dirk at ida dot ing dot tu-bs dot de>
Subject: Re: another nit.
From: Han-Wen Nienhuys <hanwen at cs dot uu dot nl>
Date: Thu, 6 Jul 2000 15:29:58 +0200 (CEST)
Cc: Michael Livshin <mlivshin at bigfoot dot com>,Guile Mailing List <guile at sourceware dot cygnus dot com>
References: <s3d7krv85l.fsf@bigfoot.com><Pine.LNX.4.21.0007061444090.14582-100000@marvin.ida.ing.tu-bs.de>
Reply-To: hanwen at cs dot uu dot nl

dirk@ida.ing.tu-bs.de writes:
> that it is an error to pass a key that is not in the alist.  Returning any
> other object is ambiguous.  Even my suggestion to have an unique tag to be
> returned if the key is not found is ambiguous:
> You can simply use this
> tag to construct another alist, where it would be a valid return

This comes in handy in my situation. If tails of the alists are shared
and therefore read-only (as they are in my application), you can
"remove" a value from the alist by consing (KEY .  #<unspecified> )
onto the list.

The problem is that #f is not ok as a tag for "does not contain the
key". (and #<unspecified> is)

-- 

Han-Wen Nienhuys   |   hanwen@cs.uu.nl    | http://www.cs.uu/~hanwen/

References:
- Re: another nit.
  - From: Michael Livshin
- Re: another nit.
  - From: Dirk Herrmann

Index Nav:	[Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav:	[Date Prev] [Date Next]	[Thread Prev] [Thread Next]