lisp-cheatsheet.org

Common Lisp Cheatsheet

This cheatsheet covers most of the stuff needed for COMP-348. Every function referenced in the lectures and tutorials should appear here. If there’s something that I missed, please let me know!

Functions and variables

Function	Example	Output	Description
defvar	(defvar x 10)	X = 10	Creates a new global variable
defun	(defun f (x) ...)	F(X) = …	Creates a new function
set	(set 'x 20)	X = 20	Sets the value of a quoted symbol.
setq	(setq x 30)	X = 30	Same as set except you don’t need to quote
setf	(setf x 40)	X = 40	Same as setq except you can set inside lists
let	(let ((x 1)) x)	X = 1	Creates a locally-scoped variable inside the block
let*	(let ((x 1) (y (+ x 2))) y)	3	Same as let, but you can use previous bindings
defconstant	(defconstant x 10)	X = 10	Creates a new global constant. Cannot change value.
boundp	(boundp 'x)	t	Returns t if symbol is bound to a value

Functions

Function	Example	Output	Description
defun	(defun f (x) ...)	F(X) = …	Creates a new function
lambda	(lambda (x) (* x 2))	<function>	An instance of a lambda function. Can be assigned to variables.
funcall	(funcall #'oddp 1)	T	Calls the given function with it’s arguments
apply	(apply #'oddp '(1))	T	Calls the given function with a list of it’s arguments

Lists

Function	Example	Output	Description
null	(null (list 1 2 3))	NIL	Returns t if the list is empty or value is nil.
listp	(listp (list 1 2 3))	T	Returns t if the element passed in is a list
list	(list 1 2 3)	‘(1 2 3)	Returns a new list of the elements passed to it.
cons	(cons 1 '(2 3))	‘(1 2 3)	Constructs a list given a head and a tail.
car	(car '(1 2 3))	1	Returns the head of a list.
cdr	(cdr '(1 2 3))	‘(2 3)	Returns the tail of a list.
append	(append '(1) '(2) '(3))	‘(1 2 3)	Appends multiple lists together.
length	(length '(1 2 3))	3	Returns the length of the given list.
member	(member 2 '(1 2 3))	‘(2 3)	Returns the list starting at the first occurence of the element
copy-list	(copy-list '(1 2 3))	‘(1 2 3)	Returns a copy of the list, copying each element.
mapcar	(mapcar #'oddp '(1 2 3))	‘(T NIL T)	Returns a new list with a given function applied to every element

Conditionals

Function	Example	Output	Description
if	(if t 10 20)	10	If the condition is true, run the first block, otherwise the second.
and	(and 10 20)	20	Return the last value, or nil if they’re not all true.
or	(or nil 10)	10	Return the first non-nil value, or nil if non are true.
cond	(cond (nil 1) (t 2))	2	Runs the first body who’s condition evaluates to true.
case	(case 'a ('a 1) (t 3))	1	Runs the first body who’s condition evaluates to true.
when	(when t (print 1) 2)	1, 2	Runs the body if the condition evaluates to true.
unless	(unless nil (print 1) 2)	1, 2	Runs the body if the condition evaluates to false.
not	(not nil)	T	Returns T if argument is NIL, returns NIL if argumnent in non-nil.

Comparisons

Function	Example	Output	Description
=	(= 1 2)	nil	Used for comparing the equality of numbers only.
<	(< 1 2)	t	Checks if all arguments are smaller than the following arguments
>	(> 1 2)	nil	Checks if all arguments are greater than the following arguments
<=	(<= 1 2)	t	Checks if all arguments are smaller than or equal to the following arguments
=>	(=> 1 2)	nil	Checks if all arguments are greater than or equal to the following arguments
eq	(eq 1 2)	nil	Checks if two numbers or characters have the same value.
eql	(eql 1 2)	nil	Checks if two values refer to the same object or are eq.
equal	(equal 1 2)	nil	Checks if two values are equal. Numbers, symbols, strings, lists, etc.

Numerical functions

Function	Example	Output	Description
numberp	(numberp 1)	T	Returns true if it’s argument is a number.
zerop	(zerop 0)	T	Returns true if it’s argument is zero.
evenp	(evenp 2)	T	Returns true if it’s argument is an even number.
oddp	(oddp 3)	T	Returns true if it’s argument is an odd number.
plusp	(plusp -1)	NIL	Returns true if it’s argument is a positive number
integerp	(integerp 1.2)	NIL	Returns true if it’s argument is an integer
+	(+ 1 2 3 4 5)	15	Takes the sum of all it’s arguments
-	(- 5 4 3 2 1)	-5	Subtracts all of it’s arguments
*	(* 1 2 3 4 5)	120	Takes the product of all it’s arguments
/	(/ 20 2 2)	5	Divides all of it’s arguments
gcd	(gcd 64 72)	8	Finds the greatest common denominator of it’s arguments
abs	(abs -3)	3	Finds the absolute value of it’s argument
sin	(sin 0)	0	Finds sin(x)
cos	(cos 0)	1	Fins cos(x)

Output

Function	Example	Output	Description
print	(print "Hello")	“Hello”	Prints it’s arguments to stdout
format	(format t "X: ~a" 'Y)	“X: Y”	Print’s it’s formatted arguments to stdout
terpri	(terpri)	“\n”	Prints a newline. Equivalent to (format t "\~%").

Predicates

Function	Example	Output	Description
boundp	(boundp 'x)	T	Returns true if symbol is bound to a value
null	(null (list 1 2 3))	NIL	Returns true if the list is empty or value is nil.
atom	(atom "hello")	T	Returns true if it’s argument is an atom or nil
listp	(listp '(1 2))	T	Returns true if it’s argument is a list or nil.
numberp	(numberp 1)	T	Returns true if it’s argument is a number.
evenp	(evenp 2)	T	Returns true if it’s argument is an even number.
oddp	(oddp 3)	T	Returns true if it’s argument is an odd number.
zerop	(zerop 0)	T	Returns true if it’s argument is zero.
plusp	(plusp -1)	NIL	Returns true if it’s argument is a positive number
integerp	(integerp 1.2)	NIL	Returns true if it’s argument is an integer
stringp	(stringp "a")	T	Returns true if it’s argument is a string.
symbolp	(symbolp 'a)	T	Returns true if it’s argument is a symbol.
keywordp	(keywordp :a)	T	Returns true if it’s argument is a keyword.

Miscellaneous

Function	Example	Output	Description
quote	(quote a)	A	Returns it’s arguments literally, as passed in.
'	'a	A	Same as quote, but a nice shorthand.
progn	(progn (print 1) 2)	1, 2	Evaluates every expression in it’s body and returns the last value.