diff --git a/LICENSE.md b/LICENSE.md deleted file mode 100644 index cba6f6a..0000000 --- a/LICENSE.md +++ /dev/null @@ -1,660 +0,0 @@ -### GNU AFFERO GENERAL PUBLIC LICENSE - -Version 3, 19 November 2007 - -Copyright (C) 2007 Free Software Foundation, Inc. - - -Everyone is permitted to copy and distribute verbatim copies of this -license document, but changing it is not allowed. - -### Preamble - -The GNU Affero General Public License is a free, copyleft license for -software and other kinds of works, specifically designed to ensure -cooperation with the community in the case of network server software. - -The licenses for most software and other practical works are designed -to take away your freedom to share and change the works. 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Additional Terms. - -"Additional permissions" are terms that supplement the terms of this -License by making exceptions from one or more of its conditions. -Additional permissions that are applicable to the entire Program shall -be treated as though they were included in this License, to the extent -that they are valid under applicable law. If additional permissions -apply only to part of the Program, that part may be used separately -under those permissions, but the entire Program remains governed by -this License without regard to the additional permissions. - -When you convey a copy of a covered work, you may at your option -remove any additional permissions from that copy, or from any part of -it. (Additional permissions may be written to require their own -removal in certain cases when you modify the work.) 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If the Program as you -received it, or any part of it, contains a notice stating that it is -governed by this License along with a term that is a further -restriction, you may remove that term. If a license document contains -a further restriction but permits relicensing or conveying under this -License, you may add to a covered work material governed by the terms -of that license document, provided that the further restriction does -not survive such relicensing or conveying. - -If you add terms to a covered work in accord with this section, you -must place, in the relevant source files, a statement of the -additional terms that apply to those files, or a notice indicating -where to find the applicable terms. - -Additional terms, permissive or non-permissive, may be stated in the -form of a separately written license, or stated as exceptions; the -above requirements apply either way. - -#### 8. 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You may not convey a covered work if you -are a party to an arrangement with a third party that is in the -business of distributing software, under which you make payment to the -third party based on the extent of your activity of conveying the -work, and under which the third party grants, to any of the parties -who would receive the covered work from you, a discriminatory patent -license (a) in connection with copies of the covered work conveyed by -you (or copies made from those copies), or (b) primarily for and in -connection with specific products or compilations that contain the -covered work, unless you entered into that arrangement, or that patent -license was granted, prior to 28 March 2007. - -Nothing in this License shall be construed as excluding or limiting -any implied license or other defenses to infringement that may -otherwise be available to you under applicable patent law. - -#### 12. No Surrender of Others' Freedom. - -If conditions are imposed on you (whether by court order, agreement or -otherwise) that contradict the conditions of this License, they do not -excuse you from the conditions of this License. If you cannot convey a -covered work so as to satisfy simultaneously your obligations under -this License and any other pertinent obligations, then as a -consequence you may not convey it at all. For example, if you agree to -terms that obligate you to collect a royalty for further conveying -from those to whom you convey the Program, the only way you could -satisfy both those terms and this License would be to refrain entirely -from conveying the Program. - -#### 13. Remote Network Interaction; Use with the GNU General Public License. - -Notwithstanding any other provision of this License, if you modify the -Program, your modified version must prominently offer all users -interacting with it remotely through a computer network (if your -version supports such interaction) an opportunity to receive the -Corresponding Source of your version by providing access to the -Corresponding Source from a network server at no charge, through some -standard or customary means of facilitating copying of software. This -Corresponding Source shall include the Corresponding Source for any -work covered by version 3 of the GNU General Public License that is -incorporated pursuant to the following paragraph. - -Notwithstanding any other provision of this License, you have -permission to link or combine any covered work with a work licensed -under version 3 of the GNU General Public License into a single -combined work, and to convey the resulting work. The terms of this -License will continue to apply to the part which is the covered work, -but the work with which it is combined will remain governed by version -3 of the GNU General Public License. - -#### 14. Revised Versions of this License. - -The Free Software Foundation may publish revised and/or new versions -of the GNU Affero General Public License from time to time. Such new -versions will be similar in spirit to the present version, but may -differ in detail to address new problems or concerns. - -Each version is given a distinguishing version number. If the Program -specifies that a certain numbered version of the GNU Affero General -Public License "or any later version" applies to it, you have the -option of following the terms and conditions either of that numbered -version or of any later version published by the Free Software -Foundation. If the Program does not specify a version number of the -GNU Affero General Public License, you may choose any version ever -published by the Free Software Foundation. - -If the Program specifies that a proxy can decide which future versions -of the GNU Affero General Public License can be used, that proxy's -public statement of acceptance of a version permanently authorizes you -to choose that version for the Program. - -Later license versions may give you additional or different -permissions. However, no additional obligations are imposed on any -author or copyright holder as a result of your choosing to follow a -later version. - -#### 15. Disclaimer of Warranty. - -THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY -APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT -HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS" WITHOUT -WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT -LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR -A PARTICULAR PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND -PERFORMANCE OF THE PROGRAM IS WITH YOU. SHOULD THE PROGRAM PROVE -DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR OR -CORRECTION. - -#### 16. Limitation of Liability. - -IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING -WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES AND/OR -CONVEYS THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, -INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES -ARISING OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT -NOT LIMITED TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR -LOSSES SUSTAINED BY YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM -TO OPERATE WITH ANY OTHER PROGRAMS), EVEN IF SUCH HOLDER OR OTHER -PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. - -#### 17. Interpretation of Sections 15 and 16. - -If the disclaimer of warranty and limitation of liability provided -above cannot be given local legal effect according to their terms, -reviewing courts shall apply local law that most closely approximates -an absolute waiver of all civil liability in connection with the -Program, unless a warranty or assumption of liability accompanies a -copy of the Program in return for a fee. - -END OF TERMS AND CONDITIONS - -### How to Apply These Terms to Your New Programs - -If you develop a new program, and you want it to be of the greatest -possible use to the public, the best way to achieve this is to make it -free software which everyone can redistribute and change under these -terms. - -To do so, attach the following notices to the program. It is safest to -attach them to the start of each source file to most effectively state -the exclusion of warranty; and each file should have at least the -"copyright" line and a pointer to where the full notice is found. - - - Copyright (C) - - This program is free software: you can redistribute it and/or modify - it under the terms of the GNU Affero General Public License as - published by the Free Software Foundation, either version 3 of the - License, or (at your option) any later version. - - This program is distributed in the hope that it will be useful, - but WITHOUT ANY WARRANTY; without even the implied warranty of - MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the - GNU Affero General Public License for more details. - - You should have received a copy of the GNU Affero General Public License - along with this program. If not, see . - -Also add information on how to contact you by electronic and paper -mail. - -If your software can interact with users remotely through a computer -network, you should also make sure that it provides a way for users to -get its source. For example, if your program is a web application, its -interface could display a "Source" link that leads users to an archive -of the code. There are many ways you could offer source, and different -solutions will be better for different programs; see section 13 for -the specific requirements. - -You should also get your employer (if you work as a programmer) or -school, if any, to sign a "copyright disclaimer" for the program, if -necessary. For more information on this, and how to apply and follow -the GNU AGPL, see . diff --git a/README.md b/README.md index cba7615..1cc75a6 100644 --- a/README.md +++ b/README.md @@ -1,61 +1,42 @@ # CL-ASYNC-AWAIT This library allows you to have async functions similar to those -in JavaScript, only these async functions are implemented with -threads instead of an event dispatching mechanism. +in JavaScript. -Cross-thread error handling is easy using `CL-ASYNC-AWAIT`, since -the `AWAIT` operator propagates errors from the promise, and also -propagates invoked restarts back to the promise. +Example: -## Simple example - -``` -(defun-async my-async-reader (stream) - (read-byte stream)) - -(defvar *promise* (my-async-reader *some-stream*)) -(defvar *my-byte* (await *promise*)) ``` +(defun-async :delay example-function (p1 p2) + (async-handler-case + (await-let* ((x p1) + (y p2)) + (/ x y)) + (division-by-zero (db0) (format *error-output* "Caught error: ~a~%" db0)))) -## Usage +(defun-async promise-value (n) n) +(defvar *p1* (example-function (promise-value 1) (promise-value 2))) +(defvar *p2* (example-function (promise-value 1) (promise-value 0))) ``` -(lambda-async lambda-list &body body) -``` -Creates a `CL:LAMBDA` function that creates a `PROMISE` when FUNCALLed. +Since Common Lisp is not a fully asynchronous language built around PROMISE objects, +it is necessary for the programmer to decide when each PROMISE will be FORCEd. + +By default, DEFUN-ASYNC and LAMBDA-ASYNC will create IMMEDIATE-PROMISEs, which +resolve as soon as they are created. Delayed promises can be created with +the :DELAY keyword, whose usage is shown for both DEFUN-ASYNC and +LAMBDA-ASYNC below: ``` -(defun-async name lambda-list &body body) +(defun-async :delay function-name lambda-list &body body) +(lambda-async :delay lambda-list &body body) ``` -Like `LAMBDA-ASYNC` but expands to a `CL:DEFUN` form instead of a `CL:LAMBDA` form. +Delayed promises will execute if and only if the FORCE method is invoked on them: ``` -(await promise) +(force promise) ``` -Wait for a `PROMISE` to resolve to one or more values. If the promise -succeeds, the values will be returned using `CL:VALUES`. - -If an error occurs in the `PROMISE` thread and is not handled within the -promise, execution of the `PROMISE` thread is suspended until the `AWAIT` -method is called. - -That error will then be signalled in the thread from which `AWAIT` is called, in -a context where all the same restarts are defined as are defined in the `PROMISE` -thread. If `INVOKE-RESTART` is called with one of these restarts, that restart -will be invoked in the `PROMISE` thread, and `AWAIT` will return that restart's value form. - -If the stack frame for the call to `AWAIT` is unwound without invoking a restart, -the `PROMISE` thread will invoke its `CL:ABORT` restart. - -Whether the `PROMISE` succeeds or fails, the result is memoized. Calling `AWAIT` a second time -on the same `PROMISE` will yield the same values. - -If an error occurred and `AWAIT` is called a second time, the same error will be signalled, but -the restarts will not be available, since the `PROMISE` thread is expected to be dead as a result -of invoking the `ABORT` restart. diff --git a/async-functions.lisp b/async-functions.lisp new file mode 100644 index 0000000..ee0aaa4 --- /dev/null +++ b/async-functions.lisp @@ -0,0 +1,99 @@ +(in-package :cl-async-await) + +(defmacro with-declare-form (var function-body &body body) + `(let ((,var (if (and (consp (car ,function-body)) + (eq (caar ,function-body) 'declare)) + (list (pop ,function-body))))) + ,@body)) + +(defmacro lambda-async (lambda-list &body body) + "Usage: + +(lambda-async lambda-list &body body) or +(lambda-async :kw lambda-list &body body) + +Expands to a CL:LAMBDA that returns a PROMISE when FUNCALLed. + +The PROMISE resolves to whatever the BODY returns. + +The :KW parameter, if provided, must be replaced with either :DELAY or +:IMMEDIATE. If :DELAY is given, the lambda will return a PROMISE +object which won't execute until its value is requested (ie, until it is +FORCEd). + +If :IMMEDIATE is given, the BODY is executed synchronously, and an +already-resolved promise will be returned. + +If no :KW argument is given, then a PARALLEL-PROMISE is created. Its +code will execute immediately in a new thread. +" + (let ((promise-type (cond ((eq lambda-list :delay) + (setf lambda-list (pop body)) + 'promise) + ((eq lambda-list :immediate) + (setf lambda-list (pop body)) + 'immediate-promise) + (t 'parallel-promise)))) + (with-declare-form declare-form body + `(lambda ,lambda-list + (make-instance ',promise-type + :thunk (lambda (resolve) + ,@declare-form + (apply resolve + (multiple-value-list + (progn ,@body))))))))) + +(defmacro defun-async (name lambda-list &body body) + "Just like LAMBDA-ASYNC, except it expands to a CL:DEFUN form instead of CL:LAMBDA." + (let ((promise-type (cond ((eq name :delay) + (setf name lambda-list) + (setf lambda-list (pop body)) + 'promise) + ((eq name :immediate) + (setf name lambda-list) + (setf lambda-list (pop body)) + 'immediate-promise) + (t 'parallel-promise)))) + (with-declare-form declare-form body + `(defun ,name ,lambda-list + ,@declare-form + (make-instance ',promise-type + :thunk (lambda (resolve) + (apply resolve + (multiple-value-list + (block ,name + ,@body))))))))) + +(defmacro await-let1 ((var promise) &body body) + (alexandria:with-gensyms (ignored-values) + `(then ,promise + (lambda (,var &rest ,ignored-values) + (declare (ignore ,ignored-values)) + ,@body)))) + +(defmacro await-let* (bindings &body body) + "Sequentially bind variables to different promises." + (unless bindings + (error "AWAIT-LET* with null BINDINGS is disallowed.")) + `(await-let1 ,(car bindings) + ,@(if (cdr bindings) + (list `(await-let* ,(cdr bindings) ,@body)) + body))) + +(defmacro await-multiple-value-bind (lambda-list promise &body body) + "Bind the multiple values returned by the PROMISE to a lambda-list." + `(then ,promise + (lambda ,lambda-list ,@body))) + +(defmacro async-handler-case (form &body cases) + "Behaves just like CL:HANDLER-CASE, except if the FORM evals to a CL-ASYNC-AWAIT:PROMISE, +it will attach error handlers to the promise and then return it." + (let ((promise (gensym))) + `(handler-case + (let ((,promise ,form)) + ,@(loop for (condition-type lambda-list . body) in cases + collect `(catch-exception ,promise ',condition-type + (lambda ,lambda-list ,@body))) + ,promise) + ,@cases))) + diff --git a/cl-async-await.asd b/cl-async-await.asd index cdc7e54..ccf4ca3 100644 --- a/cl-async-await.asd +++ b/cl-async-await.asd @@ -3,8 +3,9 @@ :version "1" :license "AGPLv3" :description "An implementation of async/await for Common Lisp" - :depends-on (:closer-mop :bordeaux-threads :simple-actors) + :depends-on (:closer-mop :bordeaux-threads) :components ((:file "package") (:file "utils" :depends-on ("package")) + (:file "async-functions" :depends-on ("package" "promise" "utils")) (:file "promise" :depends-on ("package" "utils")))) diff --git a/package.lisp b/package.lisp index 2c0ea39..3252517 100644 --- a/package.lisp +++ b/package.lisp @@ -1,4 +1,3 @@ (cl:defpackage :cl-async-await - (:use :closer-common-lisp :bordeaux-threads :simple-actors/ipc) - (:export :await :defun-async :lambda-async :promise) + (:use :closer-common-lisp :bordeaux-threads) (:shadow assoc)) diff --git a/promise.lisp b/promise.lisp index 74dfd1d..887529b 100644 --- a/promise.lisp +++ b/promise.lisp @@ -7,126 +7,123 @@ :documentation "The final values that the promise generated. Only valid if the RESOLVEDP slot is non-nil." :accessor promise-resolution) - (mutex :type lock - :initform (make-lock "PROMISE-MUTEX")) + (resolvedp :type boolean + :initform nil + :accessor promise-resolved-p) + (continuation :type function + :initarg :continuation + :initform #'values + :accessor promise-continuation) + (error-continuations :type list + :initform nil + :accessor error-continuations) (error :type (or condition null) - :initarg :error - :initform nil - :accessor promise-error) - (thread :type (or thread null) - :initarg :thread - :initform nil - :accessor promise-thread) - (outbox :type simple-actors/ipc::simple-process-mailbox - :initform (simple-actors/ipc:make-mailbox) - :reader promise-outbox) - (inbox :type simple-actors/ipc::simple-process-mailbox - :initform (simple-actors/ipc:make-mailbox) - :reader promise-inbox) + :initarg :error + :initform nil + :accessor promise-error) (thunk :type function :initarg :thunk :reader promise-thunk))) +(defclass immediate-promise (promise) () + (:documentation "A PROMISE that is FORCEd upon creation.")) + +(defclass parallel-promise (promise) + ((mutex :type lock :initform (make-lock "PARALLEL-PROMISE-MUTEX")))) + +(defgeneric force (promise) + (:documentation "Invokes the thunk attached to the PROMISE. The promise will then be +either resolved or broken.")) + +(defmethod force ((promise promise)) + (unless (or (promise-resolved-p promise) + (promise-error promise)) + (handler-case + (funcall (promise-thunk promise) + (lambda (&rest values) + (setf (promise-resolution promise) + values) + (setf (promise-resolved-p promise) t))) + (t (exn) + (loop for (type . thunk) in (error-continuations promise) + when (typep exn type) + return (funcall thunk exn)) + (setf (promise-error promise) exn) + (setf (promise-resolution promise) nil))) + (if (promise-resolved-p promise) + (apply (promise-continuation promise) + (promise-resolution promise)))) + promise) + +(defmethod force ((promise parallel-promise)) + (with-lock-held ((slot-value promise 'mutex)) + (call-next-method))) + (defmethod print-object ((promise promise) stream) - (let ((resolution-string (acond ((promise-error promise) - (format nil " Promise broken due to error: ~a" it)) - ((promise-resolution promise) - (format nil " ~a " it)) - (t " Not awaited")))) + (let ((resolution-string (cond ((promise-resolved-p promise) + (format nil " Resolved to: ~s" (promise-resolution promise))) + ((promise-error promise) + (format nil " Promise broken due to error: ~a" (promise-error promise))) + (t " Pending"))) + (continuation-string (aif (promise-continuation promise) + (format nil " Continuation: ~s" it) + ""))) - (format stream "#<~s~a>" - 'promise resolution-string))) - -(defun make-promise-handler (p) - (lambda () - (handler-bind ((error (lambda (exn) - (send-message (promise-outbox p) - `(:error ,exn - :restarts ,(loop for r in (compute-restarts) - collect `(:name ,(restart-name r) - :report ,(format nil "~a" r))))) - (let ((restart-invocation (get-message (promise-inbox p)))) - (apply #'invoke-restart restart-invocation))))) - (restart-case - (let ((result - (multiple-value-list (funcall (promise-thunk p))))) - (send-message (promise-outbox p) - `(:values ,@result))) - (abort () - :report "Terminate the promise's thread." - (send-message (promise-outbox p) '(:values))))))) - -(defmethod initialize-instance :after ((p promise) &key) - (setf (promise-thread p) - (make-thread (make-promise-handler p) - :name "PROMISE-THREAD"))) - - -(defgeneric await (promise) - (:documentation "Wait for a PROMISE to resolve to one or more values. If the promise -succeeds, the values will be returned using CL:VALUES. - -If an error occurs in the PROMISE thread, that error will be signalled in the thread -from which AWAIT is called, in a context where all the same restarts are defined -as are defined in the PROMISE thread. If INVOKE-RESTART is called with one of the -restarts defined in the PROMISE thread, that restart will be invoked in the PROMISE -thread, and AWAIT will return that restart's value form. - -If the stack frame for the call to AWAIT is unwound without invoking a restart, -the PROMISE thread will invoke its CL:ABORT restart. - -Whether the PROMISE succeeds or fails, the result is memoized. Calling AWAIT a second time -on the same PROMISE will yield the same values. - -If an error occurred and AWAIT is called a second time, the restarts will not be available, -since the PROMISE thread is expected to be dead as a result of invoking the ABORT restart.")) - -(defun raise-error-with-restarts (promise err restarts) - (let ((p promise)) - (eval `(let ((restart-invoked nil)) - (unwind-protect - (restart-case (error ,err) - ,@(loop for restart-description in restarts - collect `(,(getf restart-description :name) - (&rest restart-arguments) - :report ,(getf restart-description :report) - (setf restart-invoked t) - (send-message ,(promise-inbox p) - (cons ',(getf restart-description :name) - restart-arguments)) - (setf (promise-resolution ,p) nil) - (await-internal ,p)))) - (unless restart-invoked - (setf (promise-error ,p) ,err) - (send-message (promise-inbox ,p) '(abort)))))))) - -(defun await-internal (p) - (aif (promise-error p) - (error it) - (let ((message (or (promise-resolution p) - (setf (promise-resolution p) - (get-message (promise-outbox p)))))) - (ecase (car message) - (:values - (apply #'values (cdr message))) - (:error - (raise-error-with-restarts p (getf message :error) - (getf message :restarts))))))) - -(defmethod await ((p promise)) - (with-lock-held ((slot-value p 'mutex)) - (await-internal p))) - -(defmacro lambda-async (lambda-list &body body) - "Creates a closure that creates a PROMISE when FUNCALLed. The BODY -will run in its own thread. - -See also: AWAIT" - `(lambda ,lambda-list - (make-instance 'promise :thunk (lambda () - ,@body)))) - -(defmacro defun-async (name lambda-list &body body) - "Like LAMBDA-ASYNC but expands to a CL:DEFUN form instead of CL:LAMBDA." - `(defun ,name ,lambda-list - (make-instance 'promise :thunk (lambda () ,@body)))) + (format stream "#<~s~a;~a; ~a error continuations>" + 'promise resolution-string continuation-string + (length (error-continuations promise))))) + +(defmethod initialize-instance :after ((p immediate-promise) &key) + (force p)) + +(defmethod initialize-instance :after ((p parallel-promise) &key) + (make-thread (lambda () + (force p)) + :name "PARALLEL-PROMISE thread")) + +(defgeneric then (promise thunk) + (:documentation "Returns a new promise that will be forced when the first PROMISE's +continuation is called. The new promise resolves to the value of THUNK, +which will receive all the parameters of the continuation.")) + +(defmethod then ((promise promise) thunk) + (let* ((continuation-params nil) + (new-promise (make-instance 'promise :thunk (lambda (resolve) + (funcall resolve (apply thunk continuation-params))))) + (continuation (lambda (&rest values) + (setf continuation-params values) + (force new-promise)))) + (setf (promise-continuation promise) continuation) + (when (promise-resolved-p promise) + (apply (promise-continuation promise) + (promise-resolution promise))) + new-promise)) + +(defmethod then ((promise parallel-promise) thunk) + (with-lock-held ((slot-value promise 'mutex)) + (call-next-method))) + +(defmethod then ((not-promise t) thunk) + (make-instance 'immediate-promise + :thunk (lambda (resolve) + (funcall resolve + (funcall thunk not-promise))))) + +(defgeneric catch-exception (promise condition-type thunk)) + +(defmethod catch-exception ((promise promise) condition-type thunk) + (when (and (promise-error promise) + (typep (promise-error promise) condition-type)) + (funcall thunk (promise-error promise))) + (aif (assoc condition-type (error-continuations promise)) + (setf (cdr it) thunk) + (push (cons condition-type thunk) + (error-continuations promise))) + promise) + +(defmethod catch-exception ((promise parallel-promise) condition-type thunk) + (with-lock-held ((slot-value promise 'mutex)) + (call-next-method))) + +(defmethod catch-exception ((not-promise t) condition-type thunk) + nil) diff --git a/utils.lisp b/utils.lisp index 5c66cb8..e6be56f 100644 --- a/utils.lisp +++ b/utils.lisp @@ -10,13 +10,6 @@ (defmacro aif (cond if-true &optional if-false) `(if-let it ,cond ,if-true ,if-false)) -(defmacro acond (&body clauses) - (if (null clauses) - nil - `(aif ,(caar clauses) - (progn ,@(cdar clauses)) - (acond ,@(cdr clauses))))) - (defun (setf assoc) (new-value key alist) (aif (assoc key alist) (progn