`com.evocomputing.clos-helpers` is a small Common Lisp library providing utility functions for inspecting and working with CLOS (Common Lisp Object System) classes and instances. It leverages the Closer to MOP (Metaobject Protocol) to offer convenient ways to retrieve slot definitions, readers, writers, initargs, and map over slot values.
This library was originally extracted from the cl-mop project (MIT) and then it began to accrete more functionality as I ran across a need for more utilities dealing with the CLOS/MOP.
This library is not available via Quicklisp. To install it, git-clone into your quicklisp local-project directory:
cd ~/quicklisp/local-projects
git clone https://github.com/jolby/clos-helpersThen evaluate:
(ql:quickload :com.evocomputing.clos-helpers :force t)Here are some examples of how to use the functions provided by `com.evocomputing.clos-helpers`.
Let’s define a couple of simple classes for demonstration:
(defclass person ()
((name :initarg :name :accessor person-name)
(age :initarg :age :reader person-age)
(city :initarg :city :writer person-city)
(id :initform (gensym "ID-") :reader person-id))
(:documentation "Represents a person."))
(defclass employee (person)
((employee-id :initarg :employee-id :accessor employee-id)
(department :initarg :department)) ; No reader/writer
(:documentation "Represents an employee, inheriting from person."))
(defmethod print-object ((p person) stream)
(print-unreadable-object (p stream :type t)
(format stream "~S~%" (com.evocomputing.clos-helpers:to-plist p))))
(defmethod print-object ((e employee) stream)
(print-unreadable-object (e stream :type t)
(format stream "~S~%" (com.evocomputing.clos-helpers:to-plist e))))
(values (find-class 'person)
(find-class 'employee))You can retrieve various information about the slots of a class:
;; This is necessary for CLOS introspection, otherwise:
;; SB-MOP:CLASS-SLOTS called on #<STANDARD-CLASS COMMON-LISP-USER::EMPLOYEE>, which is not yet finalized.
;; [Condition of type SB-INT:SIMPLE-REFERENCE-ERROR]
(com.evocomputing.clos-helpers:ensure-class-finalized 'person)
(com.evocomputing.clos-helpers:ensure-class-finalized 'employee)
(com.evocomputing.clos-helpers:slot-names 'employee)
;; => (:NAME :AGE :CITY :ID :EMPLOYEE-ID :DEPARTMENT) ; Order may vary
(com.evocomputing.clos-helpers:direct-slot-names 'employee)
;; => (:EMPLOYEE-ID :DEPARTMENT) ; Order may vary
(com.evocomputing.clos-helpers:all-direct-slots 'employee)
;; => List of slot definition objects for employee and person
(com.evocomputing.clos-helpers:class-slot-exists-p 'person 'name)
;; => T
(com.evocomputing.clos-helpers:class-slot-exists-p 'person 'salary)
;; => NIL
(com.evocomputing.clos-helpers:slot-definition-for-name 'person 'age)
;; => Slot definition object for the AGE slotFunctions to find the associated reader, writer, or initarg for a specific slot:
(com.evocomputing.clos-helpers:slot-reader 'person 'name)
;; => PERSON-NAME
(com.evocomputing.clos-helpers:slot-writer 'person 'city)
;; => (SETF PERSON-CITY)
(com.evocomputing.clos-helpers:slot-initarg 'person 'age)
;; => :AGE
(com.evocomputing.clos-helpers:slot-reader 'person 'city) ; city has no reader
;; => NIL
(com.evocomputing.clos-helpers:slot-writer 'person 'age) ; age has no writer
;; => NIL
(com.evocomputing.clos-helpers:slot-initarg 'person 'id) ; id has no initarg
;; => NILYou can also get all initargs for a class:
(com.evocomputing.clos-helpers:all-slot-initargs 'employee)
;; => (:NAME :AGE :CITY :EMPLOYEE-ID :DEPARTMENT) ; Order may varyFunctions to iterate over bound slots or convert slot values to standard data structures:
(let ((emp (make-instance 'employee
:name "Alice"
:age 30
:city "Wonderland"
:employee-id "E123")))
(com.evocomputing.clos-helpers:map-slots #'list emp)
;; => ( (NAME "Alice") (AGE 30) (CITY "Wonderland") (ID #:ID-1) (EMPLOYEE-ID "E123") (DEPARTMENT NIL) ) ; Order may vary, ID is a gensym
)
(let ((emp (make-instance 'employee
:name "Bob"
:age 45
:city "Metropolis"
:employee-id "E456")))
(com.evocomputing.clos-helpers:to-alist emp)
;; => ((NAME . "Bob") (AGE . 45) (CITY . "Metropolis") (ID . #:ID-2) (EMPLOYEE-ID . "E456") (DEPARTMENT . NIL)) ; Order may vary, ID is a gensym
)
(let ((emp (make-instance 'employee
:name "Charlie"
:age 25
:city "Gotham"
:employee-id "E789")))
(com.evocomputing.clos-helpers:to-plist emp)
;; => (:NAME "Charlie" :AGE 25 :CITY "Gotham" :ID #:ID-3 :EMPLOYEE-ID "E789" :DEPARTMENT NIL) ; Order may vary, ID is a gensym
)Functions to get the actual function objects for readers and writers, useful for programmatic access:
(values
(let ((person (make-instance 'person :name "David")))
(let ((name-reader-fn (com.evocomputing.clos-helpers:slot-reader-fn 'person 'name))
(age-reader-fn (com.evocomputing.clos-helpers:slot-reader-fn 'person 'age)))
(format t "Name: ~A~%" (funcall name-reader-fn person))
(format t "Age: ~A~%" (funcall age-reader-fn person)))
person)
;; Output:
;; Name: David
;; Age: NIL ; age was not initialized
(let ((person (make-instance 'person)))
(let ((name-writer-fn (com.evocomputing.clos-helpers:slot-writer-fn 'person 'name))
(city-writer-fn (com.evocomputing.clos-helpers:slot-writer-fn 'person 'city)))
(funcall name-writer-fn person "Eve")
(funcall city-writer-fn person "Star City")
(format t "Person: ~S~%" person))
person)
)
;; Output:
;; Person: #<PERSON { ... } NAME: "Eve" CITY: "Star City" ...>Functions to get pairs of initargs and their corresponding writer function symbols or function objects. This is particularly useful for programmatically setting slot values from a plist of initargs.
(com.evocomputing.clos-helpers:initarg-writer-pair 'person 'name)
;; => (:NAME . PERSON-NAME)
(com.evocomputing.clos-helpers:all-initarg-writer-pairs 'person)
;; => ((:NAME . PERSON-NAME) (:CITY . (SETF PERSON-CITY))) ; Order may vary
;; Example of getting all initarg/writer-fn pairs:
(com.evocomputing.clos-helpers:all-initarg-writer-fn-pairs 'person)
;; => ((:NAME . #<FUNCTION ...>) (:CITY . #<FUNCTION ...>)) ; Order may vary
;; Example of using the pairs to set values from a plist:
(let ((person (make-instance 'person)))
(let ((pairs (com.evocomputing.clos-helpers:all-initarg-writer-fn-pairs 'person)))
(let ((initarg-plist '(:name "Frank" :age 50 :city "Central City"))) ; Note: :age will be ignored as there's no writer-fn pair for it
(loop for (initarg . writer-fn) in pairs
for value = (getf initarg-plist initarg)
when (and value (not (eq value :unspecified))) ; Check if value is provided and not the default nil/unspecified
do (funcall writer-fn person value)))
(format t "Person after setting: ~S~%" person))
person)
;; Output will show NAME and CITY set, but AGE will remain NIL (or its initform if any):
;; Person after setting: #<PERSON { ... } NAME: "Frank" CITY: "Central City" ...>Contributions are welcome! Please feel free to submit issues or pull requests on the GitHub repository.
This library is licensed under the MIT License. See the LICENSE file for details.