Title here
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Structs in Lisp
Our chosen language is Lisp. The code example demonstrates how to use structs to group data together. Here’s the full translation:
Go’s structs are typed collections of fields. They’re useful for grouping data together to form records.
(defstruct person
name
age)new-person constructs a new person struct with the given name.
(defun new-person (name)
(let ((p (make-person :name name)))
(setf (person-age p) 42)
p))This function safely returns a pointer to a local variable. It will only be cleaned up by the garbage collector when there are no active references to it.
(defun main ()
;; This syntax creates a new struct.
(format t "~a~%" (make-person :name "Bob" :age 20))
;; You can name the fields when initializing a struct.
(format t "~a~%" (make-person :name "Alice" :age 30))
;; Omitted fields will be zero-valued.
(format t "~a~%" (make-person :name "Fred"))
;; An & prefix yields a pointer to the struct.
(format t "~a~%" (copy-struct (make-person :name "Ann" :age 40)))
;; It’s idiomatic to encapsulate new struct creation in constructor functions.
(format t "~a~%" (new-person "Jon"))
;; Access struct fields with a dot.
(let ((s (make-person :name "Sean" :age 50)))
(format t "~a~%" (person-name s))
;; You can also use dots with struct pointers.
(let ((sp s))
(format t "~a~%" (person-age sp))
;; Structs are mutable.
(setf (person-age sp) 51)
(format t "~a~%" (person-age sp))))
;; If a struct type is only used for a single value, we don’t have to give it a name.
(let ((dog (make-struct :name "Rex" :is-good t)))
(format t "~a~%" dog)))To run the program, execute the main function.
(main)This will output:
#S(PERSON :NAME "Bob" :AGE 20)
#S(PERSON :NAME "Alice" :AGE 30)
#S(PERSON :NAME "Fred" :AGE 0)
#S(PERSON :NAME "Ann" :AGE 40)
#S(PERSON :NAME "Jon" :AGE 42)
Sean
50
51
#S((:NAME "Rex" :IS-GOOD T))Now that we can run and build basic Lisp programs, let’s learn more about the language.