On Feb 22, 2008, at 12:30, Nikodemus Siivola wrote:
How about LENGTH= ?
;; stupid version (defun length= (n seq) (= n (length seq)))
I think the idea is to have something you can use as an argument to functions like find-if. My own solution when I wanted that was functions returning closures:
my need comes from cl-rdbms: it can be configured to return resultsets both as vectors and lists, and code dealing with them is full of calls to FIRST, SECOND, LENGTH=1 and friends that should work transparently on both lists and vectors. for a short moment i wanted to suggest to shadow CL:FIRST and friends in the alexandria package with unexported versions that work on generic sequences and let users :shadowing-import-from as/when they need them. that way i could forget FIRST*. but then i realized that it's kind of like a blasphemy to talk about this, so i only hypothetically mention this idea now, hoping that i won't be thrown with stones... :) so, could this survive without any vetos? there's already FIRST-ELT in sequences.lisp... but to be specific about length=1: diff -rN -u old-alexandria/sequences.lisp new-alexandria/sequences.lisp --- old-alexandria/sequences.lisp 2008-02-22 15:53:06.000000000 +0100 +++ new-alexandria/sequences.lisp 2008-02-22 15:53:06.000000000 +0100 @@ -107,9 +107,17 @@ (list (null sequence)) (sequence (zerop (length sequence))))) +(declaim (inline length=1)) +(defun length=1 (sequence) + (declare (inline sequence-of-length-p) + (optimize speed)) + (sequence-of-length-p sequence 1)) + (defun sequence-of-length-p (sequence length) "Return true if SEQUENCE is a sequence of length LENGTH. Signals an error if SEQUENCE is not a sequence. Returns FALSE for circular lists." + (declare (type array-index length) + (optimize speed)) (etypecase sequence (null (zerop length)) -- attila