Today we will learn Lisp in One video. I’ll cover how to Install Lisp, reading input, Format, Math Functions, Equality, If, Case, When, Unless, Cond, Loop, DoTimes, Lists, Car / Cdr, , Association Lists, Functions, Optional, Receiving Multiple Values, Key, Return-From, Quasi Quoting, MapCar, Returning Multiple Values, Higher Order Functions, Lambda, Macros, Classes, Generic Functions, Inheritance, Arrays, Hash Tables, Structures, File I/O and so much more.

All of the code follows the video below. I hope you like it.

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Code From the Video

;;;; Lisp stands for List Processing, not
;;;; Lots of Irritating Superflous Parentheses
;;;; Lisps great strength is that you can use data to generate code

;;; ---------- INTRO ----------

;;; Comment
;; Comment that is indented with code
; Comment after a line of code

#||
Multiline Comment
||#

;;; ~% prints a newline with format
(format t "Hello world~%")

;;; The format statement starts with t to print to the console
;;; The control sequence begins with a ~
;;; ~a : Shows the value
;;; ~s : Shows quotes around the value
;;; ~10a : Adds 10 spaces for the value with extra space to the right
;;; ~10@a : Adds 10 spaces for the value with extra space to the left

;;; Print out a string without a newline
(print "What's your name ")

;;; Create a variable which receives the value passed by read
;;; A variable name or symbol is made of letters, numbers, and + - _ * = < > ? !
;;; and are lowercase because Lisp isn't case sensitive
;;; You can't use white space in names because list items are separated
;;; with white space
;;; Asterisks surround global variable names
(defvar *name* (read))

;;; Create a function and say hello to value passed
;;; Your supposed to keep closing parentheses on the same line, but that
;;; is up to you if the code is easier to follow
(defun hello-you (*name*)
	(format t "Hello ~a!~%" *name*)
)

;;; Change the case to capitalize just the first letter (:upcase :downcase)
(setq *print-case* :capitalize)

(hello-you *name*)

;;; A form is a list with a command function name at the beginning
;;; Everything that follows the command is sent as parameters to the function
(+ 5 4) ; = 9

;;; You can nest a form inside of a form 
(+ 5 (- 6 2)) ; = 9

;;; You define a Data Mode command by proceeding with a quote '
'(+ 5 4)

;;; Everything is a list in which each piece is held in a Cons Cell (Consecutive 
;;; Cell) [+] [5] [4] [nil] with nil defining the end of the list

;;; Change the value of a variable with setf
(setf *number* 6)

;;; You can define variables local to only the let body
;;; (let ((var-1 5) (var-2 10)) (... Body ...))

(let ((var-1 5) 
	  (var-2 10)) 
	  	(print (+ var-1 var-2))
	  	(terpri) ; Prints a newline
)

;;; ---------- FORMAT ----------

(format t "Number with commas ~:d" 10000000)

(format t "PI to 5 characters ~5f" 3.141593)

(format t "PI to 4 decimals ~,4f" 3.141593)

(format t "10 Percent ~,,2f" .10)

(format t "10 Dollars ~$ ~%" 10)

;;; ---------- MATH FUNCTIONS ----------

(format t "(+ 5 4) = ~d ~%" (+ 5 4))
(format t "(- 5 4) = ~d ~%" (- 5 4))
(format t "(* 5 4) = ~d ~%" (* 5 4))
(format t "(/ 5 4) = ~d ~%" (/ 5 4)) ; = 5/4
(format t "(/ 5 4.0) = ~d ~%" (/ 5 4.0)) ; = 1.25
(format t "(rem 5 4) = ~d ~%" (rem 5 4)) ; = 1 Returns the remainder
(format t "(mod 5 4) = ~d ~%" (mod 5 4)) ; = 1 Returns the remainder

(format t "(expt 4 2) = ~d ~%" (expt 4 2)) ; = Exponent 4^2
(format t "(sqrt 81) = ~d ~%" (sqrt 81)) ; = 9
(format t "(exp 1) = ~d ~%" (exp 1)) ; = e^1
(format t "(log 1000 10) = ~d ~%" (log 1000 10)) ; = 3 = Because 10^3 = 1000
(format t "(eq 'dog 'dog) = ~d ~%" (eq 'dog 'dog)) ; = T Check Equality
(format t "(floor 5.5) = ~d ~%" (floor 5.5)) ; = 5
(format t "(ceiling 5.5) = ~d ~%" (ceiling 5.5)) ; = 6
(format t "(max 5 10) = ~d ~%" (max 5 10)) ; = 10
(format t "(min 5 10) = ~d ~%" (min 5 10)) ; = 5
(format t "(oddp 15) = ~d ~%" (oddp 15)) ; = T Check if 15 is odd 
(format t "(evenp 15) = ~d ~%" (evenp 15)) ; = NIL = FALSE Check if 15 is even 
(format t "(numberp 2) = ~d ~%" (numberp 2)) ; = T Is 2 a number
(format t "(null nil) = ~d ~%" (null nil)) ; = T Is something equal to nil

;;; There is also sin, cos, tan, asin, acos, atan

;;; ---------- EQUALITY ----------

;;; Symbols are compared with eq

(defparameter *name* 'Derek)
(format t "(eq *name* 'Derek) = ~d ~%" (eq *name* 'Derek))

;;; Everything else is compared with equal for the most part

(format t "(equal 'car 'truck) = ~d ~%" (equal 'car 'truck))
(format t "(equal 10 10) = ~d ~%" (equal 10 10))
(format t "(equal 5.5 5.3) = ~d ~%" (equal 5.5 5.3))
(format t "(equal \"string\" \"String\") = ~d ~%" (equal "string" "String"))
(format t "(equal (list 1 2 3) (list 1 2 3)) = ~d ~%" 
	(equal (list 1 2 3) (list 1 2 3)))
	
;;; equalp can compare strings of any case and integers to floats
(format t "(equalp 1.0 1) = ~d ~%" (equalp 1.0 1))
(format t "(equalp \"Derek\" \"derek\") = ~d ~%" (equalp "Derek" "derek"))

;;; ---------- CONDITIONALS ----------

(defparameter *age* 18) ; Create variable age

;;; Relational Operators > < >= <= =

;;; Check if age is greater than or equal to 18

(if (= *age* 18)
(format t "You can vote~%")
(format t "You can't vote~%"))

;;; How to check for not equal

(if (not (= *age* 18))
(format t "You can vote~%")
(format t "You can't vote~%"))

;;; Logical Operators : and, or, not

(if (and (>= *age* 18) (<= *age* 67) )
(format t "Time for work~%")
(format t "Work if you want~%"))

(if (or (<= *age* 14) (>= *age* 67) )
(format t "You shouldn't work~%")
(format t "You should work~%"))

(defparameter *num* 2)
(defparameter *num-2* 2)
(defparameter *num-3* 2)

;;; You can execute multiple statements in an if with progn

(if (= *num* 2)
	(progn 
		(setf *num-2* (* *num-2* 2))
		(setf *num-3* (* *num-3* 3))
	)
	(format t "Not equal to 2~%"))

(format t "*num-2* = ~d ~%" *num-2*)
(format t "*num-3* = ~d ~%" *num-3*)

;;; Case performs certain actions depending on conditions
(defun get-school (age)
	(case age
		(5 (print "Kindergarten"))
		(6 (print "First Grade"))
		(otherwise '(middle school))
	))
	
(get-school 5)

(terpri) ; Newline

;;; when allows you to execute multiple statements by default

(when (= *age* 18)
	(setf *num-3* 18)
	(format t "Go to college you're ~d ~%" *num-3*)
)

;;; With unless code is executed if the expression is false

(unless (not (= *age* 18))
	(setf *num-3* 20)
	(format t "Something Random ~%")
)

;;; cond is like if else if else

(defvar *college-ready* nil)

(cond ( (>= *age* 18) ; If T do this
		(setf *college-ready* 'yes)
		(format t "Ready for College ~%"))
	  ( (< *age* 18) ; Else If T do this
	  	(setf *college-ready* 'no)
		(format t "Not Ready for College ~%"))
	  (t (format t "Don't Know ~%"))) ; Else do this by default (t is for true)
	  
;;; ---------- LOOPING ----------

;;; loop executes code a defined number of times
;;; Create a list using numbers 1 through 10
(loop for x from 1 to 10
	do(print x))

;;; Loop until the when condition calls return
(setq x 1)
(loop
	(format t "~d ~%" x)
	(setq x (+ x 1))
	(when (> x 10) (return x))
)

;;; loop for can cycle through a list or iterate commonly
;;; It will execute any number of statements after do
(loop for x in '(Peter Paul Mary) do 
	(format t "~s ~%" x)
)

(loop for y from 100 to 110 do
	(print y)
)

;;; dotimes iterates a specified number of times
(dotimes (y 12)
	(print y))

;;; ---------- CONS CELLS / LISTS ----------

;;; Link together 2 objects of data
(cons 'superman 'batman)

;;; Create a list with list
(list 'superman 'batman 'flash)

;;; Add item to the front of another list
(cons 'aquaman '(superman batman))

;;; Get the first item out of a list with car
(format t "First = ~a ~%" (car '(superman batman aquaman)))

;;; Get everything but the first item with cdr
(format t "Everything Else = ~a ~%" (cdr '(superman batman aquaman)))

;;; Get the 2nd item d = (batman flash joker) a = (batman)
(format t "2nd Item = ~a ~%" (cadr '(superman batman aquaman flash joker)))

;;; Get the 3rd item = aquaman
(format t "3rd Item = ~a ~%" (caddr '(superman batman aquaman flash joker)))

;;; Get the 4th item (Max you can go)
(format t "4th Item = ~a ~%" (cadddr '(superman batman aquaman flash joker)))

;;; Get the 4th item = joker
(format t "4th Item = ~a ~%" (cddddr '(superman batman aquaman flash joker)))

;;; Get the 2nd item in the second list
;;; d : (aquaman flash joker) (wonderwoman catwoman)
;;; a : (aquaman flash joker)
;;; d : (flash joker)
;;; a : (flash)
(format t "2nd Item 2nd List = ~a ~%" 
(cadadr '((superman batman) (aquaman flash joker) (wonderwoman catwoman))))

;;; Get the 3rd item in the 2nd list = joker
(format t "3rd Item 2nd List = ~a ~%" 
(cddadr '((superman batman) (aquaman flash joker) (wonderwoman catwoman))))

;;; = T Is something a list
(format t "Is it a List = ~a ~%" (listp '(batman superman))) 

;;; Is 3 a member of the list
(format t "Is 3 in the List = ~a ~%" (if (member 3 '(2 4 6)) 't nil)) 

;;; Combine lists into 1 list
(append '(just) '(some) '(random words))

;;; Push an item on the front of a list
(defparameter *nums* '(2 4 6))
(push 1 *nums*)

;;; Get the nth value from a list
(format t "2nd Item in the List = ~a ~%" (nth 2 *nums*)) 

;;; Create a plist which uses a symbol to describe the data
(defvar superman (list :name "Superman" :secret-id "Clark Kent"))

;;; This list will hold heroes
(defvar *hero-list* nil)

;;; Adds items to our list
(push superman *hero-list*)

;;; Cycle through all heros in the list and print them out
(dolist (hero *hero-list*)

	;; Surround with ~{ and ~} to automatically grab data from list
	(format t "~{~a : ~a ~}~%" hero)
)

;;; ---------- ASSOCIATION LIST ----------

;;; The hero name represents the key

(defparameter *heroes*
	'((Superman (Clark Kent))
	(Flash (Barry Allen))
	(Batman (Bruce Wayne))))
	
;;; Get the key value with assoc
(format t "Superman Data ~a ~%" (assoc 'superman *heroes*)) 

;;; Get secret identity
(format t "Superman is ~a ~%" (cadr (assoc 'superman *heroes*))) 
 
(defparameter *hero-size*
	'((Superman (6 ft 3 in) (230 lbs))
	(Flash (6 ft 0 in) (190 lbs))
	(Batman (6 ft 2 in) (210 lbs))))
	
;;; Get height
(format t "Superman is ~a ~%" (cadr (assoc 'Flash *hero-size*)))
 
;;; Get weight
(format t "Batman is ~a ~%" (caddr (assoc 'Batman *hero-size*))) 

;;; ---------- FUNCTIONS ----------

;;; Create a function that says hello
(defun hello ()
	(print "Hello")
	(terpri)) ; Newline
	
(hello)
	
;;; Get average
(defun get-avg (num-1 num-2)
	(/ (+ num-1 num-2) 2 ))
	
(format t "Avg 10 & 50 = ~a ~%" (get-avg 10 50)) 
	
;;; You can define some parameters as optional in a function with &optional
(defun print-list (w x &optional y z)
	(format t "List = ~a ~%" (list w x y z))
)

(print-list 1 2 3)

;;; Receive multiple values with &rest
(defvar *total* 0)

(defun sum (&rest nums)
	(dolist (num nums)
		(setf *total* (+ *total* num))
	)
	(format t "Sum: ~a ~%" *total*)
)

(sum 1 2 3 4 5)

;;; Keyword parameters are used to pass values to specific variables
(defun print-list(&optional &key x y z)
	(format t "List: ~a ~%" (list x y z))
)

(print-list :x 1 :y 2)

;;; Functions by default return the value of the last expression
;;; You can also return a specific value with return-from followed by the 
;;; function name
(defun difference (num1 num2)
	(return-from difference(- num1 num2))
)

(format t "10 - 2 = ~a ~%" (difference 10 2))	
	
;;; Get Supermans data
;;; When you use ` you are using quasiquoting which allows you to switch from 
;;; code to data mode
;;; The function between ,() is code mode
	
(defun get-hero-data (size)
	(format t "~a ~%" 
	`(,(caar size) is ,(cadar size) and ,(cddar size))))	
	
(defparameter *hero-size*
	'((Superman (6 ft 3 in) (230 lbs))
	(Flash (6 ft 0 in) (190 lbs))
	(Batman (6 ft 2 in) (210 lbs))))
	
(get-hero-data *hero-size*)

;;; Check if every item in a list is a number
(format t "A number ~a ~%" (mapcar #'numberp '(1 2 3 f g)))
 	
;;; You can define functions local only to the flet body
;;; (flet ((func-name (arguments)
;;;	... Function Body ...))
;;;	... Body ...)

(flet ((double-it (num)
		(* num 2)))
		(double-it 10))
		
;;; You can have multiple functions in flet
(flet ((double-it (num)
		(* num 2))
		(triple-it (num)
		(* num 3)))
		(format t "Double & Triple 10 = ~d~%" (triple-it (double-it 10)))
)

;;; labels is used when you want to have a function call itself, or if you want 
;;; to be able to call another local function inside a function
(labels ((double-it (num)
			(* num 2))
		(triple-it (num)
			(* (double-it num) 3)))
		(format t "Double & Triple 3 = ~d~%" (triple-it 3))
)

;;; Return multiple values from a function
(defun squares (num)
	(values (expt num 2) (expt num 3)))

;;; Get multiple values from a function
(multiple-value-bind (a b) (squares 2) 
	(format t "2^2 = ~d  2^3 = ~d~%" a b)
)

;;; Higher Order Functions
;;; You can use functions as data

(defun times-3 (x) (* 3 x))
(defun times-4 (x) (* 4 x))

;;; Pass in the function without attributes just like a variable
(defun multiples (mult-func max-num)

	;; Cycle through values up to the max supplied
	(dotimes (x max-num)
		
		;; funcall is used when you know the number of arguments
		(format t "~d : ~d~%" x (funcall mult-func x))		
))

(multiples #'times-3 10)
(multiples #'times-4 10)

;;; ---------- LAMBDA ----------

;;; The lambda command allows you to create a function without giving it a name
;;; You can also pass this function just like you pass variables

;;; Multiply every item in a list
(mapcar (lambda (x) (* x 2)) '(1 2 3 4 5))

;;; ---------- MACROS ---------- 
;;; A function runs when it is called to execute, while a macro is compiled
;;; first and is available immediately like any other lisp built in function
;;; Macros are functions used to generate code rather then perform actions

(defvar *num* 2)
(defvar *num-2* 0)

;;; It can be irritating to have to use progn with if
(if (= *num* 2)
	(progn 
		(setf *num-2* 2)
		(format t "*num-2* = ~d ~%" *num-2*)
	)
	(format t "Not equal to 2 ~%"))

(defmacro ifit (condition &rest body)

	;;; The backquote generates the code
	;;; The , changes the condition to code mode from data mode
	;;; The &rest body parameter will hold commands in a list
	;;; The "Can't Drive" Works as the else
	
	`(if ,condition (progn ,@body) (format t "Can't Drive ~%") ))

(setf *age* 16)

(ifit (>= *age* 16) 
	(print "You are over 16")
	(print "Time to Drive")
	(terpri)
)

;;; let can also get confusing with its parentheses

(defun add (num1 num2)
	(let ((sum (+ num1 num2)))
		(format t "~a + ~a = ~a ~%" num1 num2 sum)))

;;; Define a macro to clean up let

(defmacro letx (var val &body body)
	`(let ((,var ,val)) ,@body))
	
(defun subtract (num1 num2)
	(letx dif (- num1 num2)
		(format t "~a - ~a = ~a ~%" num1 num2 dif)))

(subtract 10 6)

;;; ---------- CLASSES ----------
;;; defclass defines your custom data type 
;;; Define the class name and attributes it has

(defclass animal ()
	(name
	sound))
	
;;; Create an animal object
(defparameter *dog* (make-instance 'animal))

;;; Set the values for dog
(setf (slot-value *dog* 'name) "Spot")
(setf (slot-value *dog* 'sound) "Woof")

;;; Get the values for dog
(format t "~a says ~a ~%" 
	(slot-value *dog* 'name) 
	(slot-value *dog* 'sound))

;;; You can define initialization options for objects
;;; :initarg defines the key used to assign to the slot
;;; :initform defines a default value 
;;; You can define an error message if an attribute isn't provided
;;; :accessor generates getter and setters for the slot using the name you 
;;; provide. 
;;; You could use :reader mammal-sound to generate only a getter
;;; You could use :writer (setf mammal-sound) to generate only a setter
(defclass mammal ()
	((name
		:initarg :name
		:initform (error "Must provide a name"))
	(sound
		:initarg :sound
		:initform "No Sound"
		:accessor mammal-sound)
	)
)

(defparameter *king-kong*
	(make-instance 'mammal :name "King Kong" :sound "Rawwwr")
)

;;; Output data on the mammal
(format t "~a says ~a ~%" 
	(slot-value *king-kong* 'name) 
	(slot-value *king-kong* 'sound))

;;; Displays an error because name wasn't defined
;;; (defparameter *king-kong* (make-instance 'mammal))

;;; Create mammal Fluffy
(defparameter *fluffy*
	(make-instance 'mammal :name "Fluffy" :sound "Meow")
)

;;; A generic function has a name and parameter list but no implementation
;;; In Lisp methods don't belong to classes, but instead belong to generic
;;; functions which are responsible for executing the correct method based
;;; on the data passed

(defgeneric make-sound (mammal))

(defmethod make-sound ((the-mammal mammal))
	(format t "~a says ~a ~%" 
	(slot-value the-mammal 'name)
	(slot-value the-mammal 'sound))
) 

(make-sound *king-kong*)
(make-sound *fluffy*)

;;; You can define your own getters and setters

;;; Define setter
(defgeneric (setf mammal-name) (value the-mammal))

(defmethod (setf mammal-name) (value (the-mammal mammal))
	(setf (slot-value the-mammal 'name) value))
	
;;; Define getter
(defgeneric mammal-name (the-mammal))

(defmethod mammal-name ((the-mammal mammal))
	(slot-value the-mammal 'name))
	
(setf (mammal-name *king-kong*) "Kong")

(format t "I am ~a ~%" (mammal-name *king-kong*))

;;; Use the auto generated sound getters and setters instead
(setf (mammal-sound *king-kong*) "Rawwwwwwwwr")
(format t "I say ~a ~%" (mammal-sound *king-kong*))

;;; Inheritance allows you to inherit all the attributes of the superclass
;;; and call methods that accept the superclass

(defclass dog (mammal)
	())

(defparameter *rover*
	(make-instance 'dog :name "Rover" :sound "Woof")
)

(make-sound *rover*)

;;; ---------- ARRAYS ---------- 

;;; Create an array with 3 storage areas
(defparameter names (make-array 3))

;;; Add a value to an array
(setf (aref names 1) 'Bob)

;;; Get a value in an index
(aref names 1)

;;; Make a 3 by 3 array
(setf num-array (make-array '(3 3)
	:initial-contents '((0 1 2) (3 4 5) (6 7 8))))
	
;;; Cycle through and print the array
(dotimes (x 3)
	(dotimes (y 3)
		(print (aref num-array x y))
	)
)

;;; ---------- HASH TABLE ---------- 
;;; A collection of key value pairs

;;; Create a hash table
(defparameter people (make-hash-table))

;;; Set the key as 102 and the value to Paul Smith
(setf (gethash '102 people) '(Paul Smith))
(setf (gethash '103 people) '(Sam Smith))

;;; Get the value stored in the key 102
(gethash '102 people)

;;; maphash executes a function on each item
;;; ~% = newline
(maphash #'(lambda (k v) (format t "~a = ~a~%" k v)) people)

;;; Remove an entry with the key
(remhash '103 people)

;;; ---------- STRUCTURES ----------
;;; A user defined data type with multiple different data types

;;; Define the data names in the struct
(defstruct customer name address id)

;;; Store data in the struct
(setq paulsmith (make-customer 
	:name "Paul Smith"
	:address "123 Main St"
	:id 1000
))

;;; Get a value stored
(customer-name paulsmith)

;;; Change a value in the struct
(setf (customer-address paulsmith) "125 Main St")
(write paulsmith)

(setq sally-smith-1001 (make-customer 
	:name "Sally Smith"
	:address "123 Main St"
	:id 1001
))

;;; ---------- FILE I O ---------- 

;;; Write text to a file
;;; A keyword symbol starts with a colon and it only means itself
(with-open-file (my-stream
				"test.txt"
				:direction :output ; We are writing to the file
				:if-exists :supersede) ; If the file exists delete it
	(princ "Some random Text" my-stream))

;;; Read data from a file
(let ((in (open "test.txt" :if-does-not-exist nil)))
   (when in
      (loop for line = (read-line in nil)
      while line do (format t "~a~%" line))
      (close in)
   )
)