alexandria-devel May 2009

alexandria-devel@common-lisp.net

1 participants
4 discussions

[alexandria-devel] Review cycle 2: SWITCH, ESCWITCH, and CSWITCH
by Nikodemus Siivola 08 Apr '10

08 Apr '10

macro switch ((object &key test key) &body clauses) "Evaluates first matching clause, returning its values, or evaluates and returns the values of DEFAULT if no keys match." macro eswitch ((object &key test key) &body clauses) "Like SWITCH, but signals an error if no key matches." cswitch ((object &key test key) &body clauses) "Like SWITCH, but signals a continuable error if no key matches."

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[alexandria-devel] cdr assoc (now called alist-get)
by John Fremlin 25 Nov '09

25 Nov '09

For http://common-lisp.net/project/cl-irregsexp/ and in fact for many other projects, it is quite handy to have a way of storing key value pairs in a table that is more lightweight than a hashtable, and that preserves ordering. The obvious way to do it in Lisp is to store a list like '((key0 . value0) (key1 . value1) ...) However in the ANSI standard there is no easy way to implement (setf (gethash key table) value). (cdr (assoc ...)) is sufficient for lookup. To that end there is commonly available in extensions a (setf cdr-assoc). I posted one to the list before but I had managed to mangle it utterly in my last edit of it and it didn't work. I hope that was why you Alexandrians ignored me . . . Anyway, one problem with cdr-assoc is that the order of parameters is apparently non-standard. To alleviate this problem I have come back with a new name, alist-get and also ralist-get (for cdr-rassoc, the (value.key) convention). Feedback very much appreciated! (declaim (inline racons)) (defun racons (key value ralist) (acons value key ralist)) (macrolet ((define-alist-get (name get-pair get-value-from-pair add) `(progn (declaim (inline ,name)) (defun ,name (alist key &key (test 'eql)) (let ((pair (,get-pair key alist :test test))) (values (,get-value-from-pair pair) pair))) (define-setf-expander ,name (place key &key (test ''eql) &environment env) (multiple-value-bind (dummies vals newvals setter getter) (get-setf-expansion place env) (when (cdr newvals) (error "~A cannot store multiple values in one place" ',name)) (with-unique-names (store key-val test-val alist found) (values `(,@dummies ,key-val ,test-val) `(,@vals ,key ,test) (list store) `(let ((,alist ,getter)) (let ((,found (,',get-pair ,key-val ,alist :test ,test-val))) (cond (,found (setf (,',get-value-from-pair ,found) ,store)) (t (let ,newvals (setf ,(first newvals) (,',add ,key ,store ,alist)) ,setter))) ,store)) `(,',name ,getter ,key)))))))) (define-alist-get alist-get assoc cdr acons) (define-alist-get ralist-get rassoc car racons))

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[alexandria-devel] darcs patch: Add #.#+ readtime conditional functions.
by asf＠boinkor.net 02 Oct '09

02 Oct '09

Mon Oct 16 10:00:31 CEST 2006 asf(a)boinkor.net * Add #.#+ readtime conditional functions. * This adds functions that can be used in #+#. readtime conditionals, for example: #+#.(alexandria:read-if (find-package :asdf-install)) :yay #+#.(alexandria:read-if-fbound :install :asdf-install :exportedp t) :yay * included in the patch is a commented-out portion that allows the user to activate a #? read syntax. I'm not sure if that fits into the conservativism constraints.

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[alexandria-devel] Adding ignorability to once-only
by John Fremlin 24 May '09

24 May '09

Dear Alexandrians, Thanks for your great library. However, consider this (on SBCL) CL-USER> (macrolet ((m (x) (alexandria:once-only (x) (declare (ignore x)) t))) (m t)) ; in: LAMBDA NIL ; (LET ((#:X871 T)) ; T) ; ; caught STYLE-WARNING: ; The variable #:X871 is defined but never used. ; ; compilation unit finished ; caught 1 STYLE-WARNING condition T CL-USER> (macrolet ((m (x) (alexandria:once-only (x) `(locally (declare (ignorable ,x)) t)))) (m t)) ; in: LAMBDA NIL ; (LOCALLY (DECLARE (IGNORABLE #:X830)) T) ; ; caught STYLE-WARNING: ; declaring unknown variable #:X830 to be ignored ; (LET ((#:X830 T)) ; (LOCALLY (DECLARE (IGNORABLE #:X830)) T)) ; ; caught STYLE-WARNING: ; The variable #:X830 is defined but never used. In complex macros sometimes it's nice to be able to declare a once-only variable ignorable. I've been using this version in my fast Lisp webserver. http://github.com/vii/teepeedee2/tree/master (defun force-first (x) (if (listp x) (first x) x)) (defun force-rest (x) (when (listp x) (rest x))) (defmacro once-only ((&rest names-and-decls) &body body) ;; Each name is already lexically bound to something in the macro M using once-only ;; For each NAME: ;; - Generate a unique symbol SYM with value a unique symbol SYM-VAL ;; - In the macro-expansion of M, bind SYM-VAL to the value of NAME ;; - For BODY, bind NAME to SYM ;; It is necessary to use the indirection SYM -> SYM-VAL so that a ;; new symbol will be created for each invocation of M, not just ;; for each invocation of once-only (let* ((names (mapcar 'force-first names-and-decls)) (declarations (mapcar 'force-rest names-and-decls)) (symbols (loop for name in names collect (gensym (string name))))) `(let ,(loop for symbol in symbols for name in names collect `(,symbol (gensym ,(string name)))) `(let ,(list ,@(loop for name in names for symbol in symbols collect `(list ,symbol ,name))) ,@(list ,@(loop for symbol in symbols for decl in declarations append (loop for d in decl collect ``(declare (,@,(if (listp d) d `(list `,',d)) ,,symbol))))) ,(let ,(loop for symbol in symbols for name in names collect `(,name ,symbol)) ,@body))))) I wrote this macro when I was quite unfamiliar with Lisp. I'm sure you can think a better syntax and can improve it. The result is syntax like this CL-USER> (macrolet ((m (x) (once-only ((x ignorable)) (declare (ignore x)) t))) (m t)) T

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alexandria-devel May 2009