From ...
From: Erik Naggum <erik@naggum.net>
Subject: Re: Get subseq of alist using regexp mathcing on cars
Date: 2000/07/26
Message-ID: <3173631943791755@naggum.net>#1/1
X-Deja-AN: 651124041
References: <8ln0j7$1qa$1@newsx.cc.uic.edu> <8ln4d4$2kk$1@newsx.cc.uic.edu>
mail-copies-to: never
Content-Type: text/plain; charset=us-ascii
X-Complaints-To: newsmaster@eunet.no
X-Trace: oslo-nntp.eunet.no 964643352 11665 195.0.192.66 (26 Jul 2000 20:29:12 GMT)
Organization: Naggum Software; vox: +47 8800 8879; fax: +47 8800 8601; http://naggum.no; http://naggum.net
User-Agent: Gnus/5.0803 (Gnus v5.8.3) Emacs/20.7
Mime-Version: 1.0
NNTP-Posting-Date: 26 Jul 2000 20:29:12 GMT
Newsgroups: comp.lang.lisp

* "Bruce Lambert" <lambertb@uic.edu>
| This is what I came up with myself.  It seems to work in the simple
| case where the cars are all single-character symbols.  This will
| work for my current application.  It could, of course, be much
| fancier.  I still welcome suggestions.

  I must admit to not having understood your original request, as
  "assoc" is just not what you're asking for.

| "Takes a regular expression and an alist and returns the subsequence
| of alist whose cars match the regexp.  Assume cars are all symbols
| whose print-names are single characters."

  It doesn't really assume that.  The cars may be one-character
  strings, characters, or symbols with one-character names.

(defun regexp-subseq (sequence regexp &key (key #'car))
  (destructuring-bind (match &optional (start . end))
      (multiple-value-list
       (match-regexp regexp
                     (map 'string (compose #'character key) sequence)
		     :return :index))
    (if match
        (subseq sequence start end)
      nil)))

  compose is either a macro or a function that composes functions.  In
  this case, it produces (lambda (x) (character (funcall key x))).

#:Erik
-- 
  If this is not what you expected, please alter your expectations.