Subject: Re: Get subseq of alist using regexp mathcing on cars
From: Erik Naggum <>
Date: 2000/07/26
Newsgroups: comp.lang.lisp
Message-ID: <>

* "Bruce Lambert" <>
| 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))
       (match-regexp regexp
                     (map 'string (compose #'character key) sequence)
		     :return :index))
    (if match
        (subseq sequence start end)

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

  If this is not what you expected, please alter your expectations.