Lisp: Common Lisp, Racket, Clojure, Emacs Lisp

a side-by-side reference sheet

grammar and invocation | variables and expressions | arithmetic and logic | strings | lists
arrays | dictionaries | functions | execution control | file handles | file buffers | files | directories | processes and environment | libraries and namespaces | objects | macros | reflection | java interop

common lisp racket clojure emacs lisp
version used
 
SBCL 1.0.48 Racket 5.1 Clojure 1.2 Emacs 24.1
show version
 
$ sbcl --version $ racket --version displayed by repl on startup $ emacs --version
grammar and invocation
common lisp racket clojure emacs lisp
compiler $ mzc module.rkt M-x byte-compile-file
making a standalone executable (sb-ext:save-lisp-and-die
  "executable"
  :executable t
  :toplevel 'function)
$ mzc —exe executable file see note
shebang #!/usr/bin/env sbcl --script #!/usr/bin/env racket --script specify full path to clojure jar:
#!/usr/bin/env java -jar clojure.jar
#!/usr/bin/env emacs --script
repl
 
$ sbcl $ racket $ java -jar /PATH/TO/clojure.jar M-x ielm
word separator whitespace whitespace whitespace and commas whitespace
are identifiers case sensitive?
 
no yes yes yes
identifier characters everything except whitespace and:
( ) " , ' ` : ; # | \

reserved for user macros:
? ! [ ] { }
everything except whitespace and:
( ) [ ] { } " , ' ` ; # | \
alphanumerics and these:
* + ! - _ ?

these have special meaning or are reserved:
/ . :
everything except whitespace and:
( ) " , ' ` ; # | \ _ [ ]
escaping characters in identifiers (setq white\ space\ symbol 3) racket:
(define white\ space\ symbol 3)
none (setq white\ space\ symbol 3)
quoting characters in identifiers (setq |white space symbol| 3) (define |white space symbol| 3) none none
end-of-line comment (+ 1 1) ; adding (+ 1 1) ; adding (+ 1 1) ; adding (+ 1 1) ; adding
multiple line comment (+ 1 #| adding |# 1) r6rs:
(+ 1 #| adding |# 1)
variables and expressions
common lisp racket clojure emacs lisp
label
 
set,setq,defun define def,defn set,setq,defun
quote
 
quote quote quote quote
cell types
 
value, function, struct, class, … value value value, function, struct, …
null nil null nil nil
null test (null foo) (null? foo) (nil? foo) (null foo)
is the empty list null? yes yes no yes
is null literal a symbol? yes yes no yes
type predicates null symbolp atom consp listp numberp characterp stringp null? symbol? none pair? list? number? char? string?
racket: cons? synonym for pair?
nil? symbol? none none list? number? none string? null symbolp atom consp listp numberp characterp stringp
set property
 
(setf (get 'foo :prop) 13) none (def foo (with-meta 'x { :prop 13 })) (setf (get 'foo :prop) 13)
get property
 
(get 'foo :prop) none (get (meta foo) :prop) (get 'foo :prop)
remove property (remprop 'foo :prop) none none (remprop 'foo :prop)
quoted symbol 'foo
(quote foo)
'foo
(quote foo)
'foo
(quote foo)
'foo
(quote foo)
keyword
 
:foo #:foo :foo :foo
arithmetic and logic
common lisp racket clojure emacs lisp
true and false t nil #t #f
racket: true false
true false t nil
falsehoods nil () #f
racket: #f false
false nil nil ()
is true a symbol? yes no no yes
logical operators (or (not t) (and t nil)) (or (not #t) (and #t #f)) (or (not true) (and true false)) (or (not t) (and t nil))
relational operators = /= < > <= >= = none < > <= >= = none < > <= >= = /= < > <= >=
eq, equal, = eq, equal, = eq?, equal?, = = works on symbols and is true for lists with identical members eq, equal, =
min and max (min 1 2 3)
(max 1 2 3)
(min 1 2 3)
(max 1 2 3)
(min 1 2 3)
(max 1 2 3)
(min 1 2 3)
(max 1 2 3)
numeric predicates numberp integerp
rationalp floatp
realp complexp
number? integer?
rational? inexact?
real? complex?
number? integer?
rational? float?
none none
numberp integerp
none floatp
none none
arithmetic operators + - * / mod + - * / modulo + - * / mod + - * / %
algebraic notation
integer division
and remainder
(truncate 7 3)
(rem 7 3)
(quotient 7 3)
(remainder 7 3)
(quot 7 3)
(rem 7 3)
(/ 7 3)
(% 7 3)
integer division by zero arith-error
float division rational:
(/ 7 3)

float:
(/ 7 (* 3 1.0))
rational:
(/ 7 3)

float:
(/ 7 (float 3))
rational:
(/ 7 3)

float:
(/ 7 (* 3 1.0))
integer quotient:
(/ 7 3)

float:
(/ 7 (* 3 1.0))
float division by zero -1.0e+INF, -0.0e+NaN, or 1.0e+INF
power (expt 2 32) (expt 2 32) returns float:
(Math/pow 2 32)
(expt 2 32)
sqrt (sqrt 2) (sqrt 2) (Math/sqrt 2) (sqrt 2)
sqrt -1 #C(0.0 1.0) 0+1i (Math/sqrt -1): NaN -0.0e+NaN
transcendental functions exp log sin cos tan asin acos atan atan exp log sin cos tan asin acos atan atan Math/exp Math/log Math/sin Math/cos Math/tan Math/asin Math/acos Math/atan Math/atan2 exp log sin cos tan asin acos atan atan
float truncation return two values, first is integer:
truncate round ceiling floor
return floats:
truncate round ceiling floor
return integers:
int Math/round
return floats:
Math/ceil Math/floor
truncate round ceiling floor
fround fceiling ffloor
truncate returns integer
absolute value
and signum
abs signum abs
racket: sgn
Math/abs Math/signum abs signum
rational decomposition numerator denominator numerator denominator (.numerator x)
(.denominator x)
none none
complex decomposition realpart imagpart real-part imag-part none
none
none none
random number
uniform integer, uniform float, normal float
(random 100)
(random 1.0)
none
gambit and srfi 27:
(random-integer 100)
(random-real)
none
 
racket:
(random 100)
(random)
none
(def rnd (java.util.Random.))
(.nextInt rnd 100)
(.nextFloat rnd)
(.nextGaussian rnd)
(random 100)
none
none
random seed
bit operators ash left shift when 2nd argument positive logand logior logxor lognot arithmetic-shift left shift when 2nd argument positive bitwise-and bitwise-ior bitwise-xor bitwise-not bit-shift-left bit-shift-right bit-and bit-or bit-xor bit-not lsh left shift when 2nd argument positive logand logior logxor lognot
strings
common lisp racket clojure emacs lisp
character literals #\a #\Space #\Newline #\Backspace #\Tab #\Linefeed #\Page #\Return #\Rubout #\a #\space #\newline #\backspace #\tab #\linefeed #\page #\return #\nul #\vtab #\alarm #\esc #\delete
not in racket: #\alarm #\esc #\delete
\a \newline \space \backspace \tab ? \formfeed \return ? ?a ?\b ?\t ?\n ?\f ?\r ?\" ?\\ ?\ooo ?\uhhhh ?\xh - ?\xhhhhhh ?\C-x ?\M-x
string literal
 
"foo bar" "foo bar" "foo bar" "foo bar"
string escapes \" \\ \t \n \r \" \\ \ooo \uhhhh \b \t \n \f \r \" \\ \ooo \uhhhh \b \t \n \f \r \" \\ \ooo \uhhhh \xh - \xhhhhhh \C-x \M-x
character access (char "foo" 0) (string-ref "foo" 0) (.charAt "foo" 0) (aref "foo" 0)
find substring (search "bar" "foo bar") racket:
(require srfi/13/string)
(string-contains "foo bar" "bar")
(.indexOf "foo bar" "bar") (search "bar" "foo bar")
extract substring (subseq "foo bar" 4 7) (substring "foo bar" 4 7) (.substring "foo bar" 4 7) (substring "foo bar" 4 7)
length
 
(length "foo") (string-length "foo") (.length "foo") (length "foo")
constructors (make-string 3 :initial-element #\f)
 
(reduce (lambda (m o)
    (concatenate 'string m
      (string o)))
  '(#\f #\o #\o)
  :initial-value "")
(make-string 3 #\f)
 
(string #\f #\o #\o)
(String. (into-array
  (. Character TYPE)
  (repeat 3 \f)))
 
(String. (into-array
  (. Character TYPE)
  '(\f \o \o)))
(make-string 3 ?f)
 
(string ?f ?o ?o)
comparison (string= "foo" "bar")
(string< "foo" "bar")
(string=? "foo" "bar")
(string<? "foo" "bar")
(.equals "foo" "bar")
(.compareTo "foo" "bar")
(string= "foo" "bar")
(string< "foo" "bar")
case (string-downcase "FOO")
(string-upcase "foo")
(string-capitalize "foo")
(string-downcase "FOO") (.toLowerCase "FOO") (downcase "FOO")
(upcase "foo")
(capitalize "foo")
trim (string-trim
  '(#\Space #\Tab #\Newline)
  " foo ")
(require srfi/13/string)
(string-trim-both " foo ")
(.trim " foo ") none; see notes for an implementation
concat (concatenate 'string
  "foo "
  "bar "
  "baz")
(string-append
  "foo "
  "bar "
  "baz")
(str "foo " "bar " "baz") (concat "foo " "bar " "baz")
convert from string, to string (+ 7 (parse-integer "12"))
 
(+ 73.9 (read-from-string ".037"))
 
(concatenate 'string
  "value: "
  (princ-to-string 8))
(+ 7 (string->number "12"))
 
(+ 73.9 (string->number ".037"))
 
(string-append
  "value: "
  (number->string 8))
(+ 7 (Integer/parseInt "12"))
 
(+ 73.9 (Float/parseFloat ".037"))
 
(str "Value: " 8)
(+ 7 (string-to-number "12"))
 
(+ 73.9
  (string-to-number ".037"))
 
(concat
  "value: "
  (number-to-string 8))
split (cl-ppcre:split
  "[ \t\n]+"
  "foo bar baz")
(regexp-split #rx"[ \n\t]+"
  "foo bar baz")
(seq
  (.split "foo bar baz"
    "[ \t\n]+"))
(split-string "foo bar baz")
join (reduce
  (lambda (m o)
    (concatenate 'string m " " o))
  '("foo" "bar" "baz"))
(string-join
  '("foo" "bar" "baz")
  " ")
(reduce #(str %1 " " %2)
  '("foo" "bar" "baz"))
(reduce
  (lambda (m o) (concat m " " o))
  '("foo" "bar" "baz"))
format (format nil "~a: ~a ~,2F"
  "Foo"
  7
  13.457)
(format "~a ~a ~a" "Foo" 7 13.457) (String/format "%s: %d %.2f"
  (to-array ["Foo" 7 13.457]))
(format "%s: %d %.2f"
  "Foo"
  7
  13.457)
regular expressions (cl-ppcre:all-matches
  "bar"
  "foo bar")
(regexp-match #rx"bar" "foo bar") (re-seq #"bar" "foo bar") (string-match "bar" "foo bar")
regex substitution (cl-ppcre:regex-replace "[^l]l"
  "hello"
  "EL")
 
(cl-ppcre:regex-replace-all "[^l]l"
  "hello hello"
  "EL")
(regexp-replace #rx"el"
  "hello"
  "EL")
 
(regexp-replace* #rx"el"
  "hello hello"
  "EL")
(.replaceFirst "hello" "[^l]l" "XX")
 
(.replaceAll "hello hello"
  "[^l]l" "XX")
?
 
(replace-regexp-in-string "[^l]l"
  "EL"
  "hello hello")
regex special characters (cl-ppcre:all-matches
  "^[0-9a-f]+$"
  "1ab7")
 
(cl-ppcre:all-matches
  "(\\d\\w\\s)\\1"
  "8a 8a ")
(regexp-match #rx"^[a-f0-9]+$"
  "1ab7")
 
(regexp-match #px"(\\d\\w\\s)\\1"
  "8a 8a ")
(re-seq #"^[0-9a-f]+$" "1ab7")
 
(re-seq #"(\d\w\s)\1" "8a 8a ")
(string-match
  "^[0-9a-f]+$"
  "1abf")
lists
common lisp racket clojure emacs lisp
list literal
 
'(1 2 3) '(1 2 3) or '[1 2 3] or '{1 2 3} '(1 2 3) '(1 2 3)
pair literal
 
'(1 . 2) '(1 . 2) none '(1 . 2)
car
 
car, first car racket: car, first first car
cdr
 
cdr, rest cdr racket: cdr, rest rest, next cdr
cons
 
cons cons cons 2nd arg must be a list cons
atom
 
(atom x) (not (pair? x)) (not (list? x)) (atom x)
(car '())
 
nil error first: nil nil
(cdr '()) nil error rest: ()
next: nil
nil
(eval '())
 
nil error () nil
list functions
 
list listp length append reverse list list? length append reverse list list? count concat reverse list listp length append reverse
nth
 
(nth 3 '(0 1 2 3)) (list-ref '(0 1 2 3) 3) (nth '(0 1 2 3) 3) (nth 3 '(0 1 2 3))
index of list element (position 7 '(5 6 7 8)) srfi-1:
(list-index
  (lambda (x) (= x 7))
  '(5 6 7 8))
none (position 7 '(5 6 7 8))
last butlast (setq a '(1 2 3))
(car (last a))
(butlast a)
racket:
(define a '(1 2 3))
(last a)
(take a (- (length a) 1))
(def a '(1 2 3))
(last a)
(butlast a)
(car (last a))
(butlast a)
set-car set-cdr (setq a '(1 2 3))
(setf (car a) 3)
(setf (cdr a) '(4 5 6))
r5rs only:
(define a '(1 2 3))
(set-car! a 3)
(set-cdr! a '(4 5 6))
none (setq a '(1 2 3)
(setcar a 3)
(setcdr a '(4 5 6))
sort
 
(sort '(3 2 4 1) '<) (sort '(3 2 4 1) <) (sort < '(3 2 4 1)) (sort '(3 2 4 1) '<)
assoc
 
(assoc 3 '((1 2) (3 4))) (assoc 3 '((1 2) (3 4))) none, see note (assoc 3 '((1 2) (3 4)))
getf
 
(getf '(1 2 3 4) 3) none none (getf '(1 2 3 4) 3)
map (mapcar
  (lambda (x) (* x x))
  '(1 2 3))
(map (lambda (x) (* x x)) '(1 2 3)) (map #(* % %) '(1 2 3)) (mapcar
  (lambda (x) (* x x))
  '(1 2 3))
filter (remove-if-not
  (lambda (x) (> x 2))
  '(1 2 3))
remove-if returns complement
racket and srfi-1:
(filter
  (lambda (x) (> x 2))
  '(1 2 3))
filter-not returns complement
(filter #(> % 2) '(1 2 3))
remove returns complement
(remove-if-not
  (lambda (x) (> x 2))
  '(1 2 3))
remove-if returns complement
reduce (left fold) (reduce '-
  '(1 2 3 4)
  :initial-value 0)
srfi-1:
(fold - 0 '(1 2 3 4))
racket:
(foldl - 0 '(1 2 3 4))
(reduce - 0 '(1 2 3 4)) (reduce '-
  '(1 2 3 4)
  :initial-value 0)
right fold (reduce '-
  '(1 2 3 4)
  :initial-value 0
  :from-end t)
srfi-1:
(fold-right - 0 '(1 2 3 4))
racket:
(foldr - 0 '(1 2 3 4))
none (reduce '-
  '(1 2 3 4)
  :initial-value 0
  :from-end t)
sublis (sublis '((1 . 2) (3 . 4))
  '(1 (3 3 (1))))
(sublis '((1 . 2) (3 . 4))
  '(1 (3 3 (1))))
dolist (dolist (x '(1 2 3))
  (print x)
  (print (- x)))
racket:
(for ((x '(1 2 3)))
  (printf "~a~n" x)
  (printf "~a~n" (- x)))
(doseq [x '(1 2 3)]
  (println x)
  (println (- x)))
(dolist (x '(1 2 3))
  (print x)
  (print (- x)))
universal predicate (every
  (lambda (i) (= 0 (rem i 2)))
  '(1 2 3 4))
racket:
(for/and ((i '(1 2 3 4)))
  (= 0 (remainder i 2)))
(every? #(= 0 (rem % 2)) '(1 2 3 4)) (every
  (lambda (i) (= 0 (% i 2)))
  '(1 2 3 4))
existential predicate (some
  (lambda (i) (= 0 (rem i 2)))
  '(1 2 3 4))
racket:
(for/or ((i '(1 2 3 4)))
  (= 0 (remainder i 2)))
(some #(= 0 (rem % 2)) '(1 2 3 4)) (some
  (lambda (i) (= 0 (% i 2)))
  '(1 2 3 4))
take none racket and srfi-1:
(take '(1 2 3 4) 2)
(take 2 '(1 2 3 4)) none
drop (nthcdr 2 '(1 2 3 4)) racket and srfi-1:
(drop '(1 2 3 4) 2)
(drop 2 '(1 2 3 4)) (nthcdr 2 '(1 2 3 4))
push and pop (setq x '(1 2 3))
(push 4 x)
(pop x)
none (def x '(1 2 3)
none
(pop x)
(setq x '(1 2 3))
(push 4 x)
(pop x)
arrays
common lisp racket clojure emacs lisp
vector literal
 
#(1 2 3) #(1 2 3) [1 2 3] [1 2 3]
vector access (elt #(1 2 3) 0) or
(aref #(1 2 3) 0)
(vector-ref #(1 2 3) 0) (nth [1 2 3] 0) (elt [1 2 3] 0)
set vector element (setq v [1 2 3])
(setf (aref v 2) 4)
(define v (vector 1 2 3))
(vector-set! v 2 4)
(replace { 2 4 } [1 2 3]) (setq v #(1 2 3))
(setf (aref v 2) 4)
vector to list
 
(coerce #(1 2 3) 'list) (vector->list #(1 2 3)) (seq [1 2 3]) (coerce [1 2 3] 'list)
list to vector
 
(coerce '(1 2 3) 'vector) (list->vector '(1 2 3)) (vec '(1 2 3)) (coerce '(1 2 3) 'vector)
sequence data types list vector list vector hash-table string input-port range all collections and strings list vector
sequence predicate (typep '(1 2 3) 'sequence)
(typep #(1 2 3) 'sequence)
(sequence? '(1 2 3)) (seq? '(1 2 3))
(seq? (seq [1 2 3]))
(typep '(1 2 3) 'sequence)
(typep [1 2 3] 'sequence)
list functions usable on sequences length reduce remove-if-not sort for for/list for/hash for/and for/or for/fold vectors support all list functions; seq will convert any other collection to an object which supports list functions length reduce remove-if-not
make-array (make-array '(4 3 2)
  :initial-element 0)
 
(make-array '(3 2)
  :initial-contents
  '((1 2) (3 4) (5 6)))
none none none
array access (setq a
  (make-array '(3 2)
    :initial-contents
    '((1 2) (3 4) (5 6))))
 
(aref a 2 1)
none none none
set array element (setf (aref a 2 1) 7) none none none
array dimensions (setq a
  (make-array '(4 3 2)
    :initial-element 0))
 
(array-rank a)
(array-dimensions a)
(array-dimension a 0)
none none none
range none (in-range 1 101) use in for constructs (range 1 101) none
list comprehension none (for*/list ((file "ABCDEFGH") (rank (in-range 1 9))) (printf "~a~a" file rank)) (for [file "ABCDEFGH" rank (range 1 9)] (format "%c%d" file rank)) none
dictionaries
common lisp racket clojure emacs lisp
make-hash (setq h (make-hash-table)) (define h (make-hash))
(define ih (make-immutable-hash '(("hello" . 5))))
(def h (hash-map "hello" 5)) (setq h
  (make-hash-table
    :test 'equal))
hash literal
 
none #hash(("hello" . 5) ("goodbye" . 7)) {"hello" 5 "goodbye" 7} none
put-hash (setf (gethash "hello" h) 5) (hash-set! h "hello" 5)
(define ih2 (hash-set ih "goodbye" 7))
none
(def h2 (assoc h "goodbye" 7))
(puthash "hello" 5 h)
get-hash
 
(gethash "hello" h) (hash-ref h "hello") (get h "hello") (gethash "hello" h)
hash key not found nil error nil nil
rem-hash (remhash "hello" h) (hash-remove! h "hello")
 
(define ih2
  (hash-remove ih "hello"))
none
(def h2 (dissoc h "hello"))
(remhash "hello" h)
hash size
 
(hash-table-count h) (hash-count h) (count h) (hash-table-count h)
iterate over hash entries (maphash
  (lambda (k v)
    (print k)
    (print v))
  h)
(hash-for-each h
  (lambda (k v)
    (printf "~a~n" k)
    (printf "~a~n" v)))
(doseq [p h]
  (println (first p))
  (println (second p)))
(maphash
  (lambda (k v)
    (print k)
    (print v))
  h)
map hash to list none (define hkeys (hash-map h (lambda (k v) k)))
(define hvals (hash-map h (lambda (k v) v)))
(def hkeys (map (fn [p] (first p)) h))
(def hvals (map (fn [p] (second p)) h))
none
defstruct (defstruct account id balance) (define-struct account (id (balance #:mutable))) (defstruct account :id :balance) (defstruct account id balance)
struct (setq a
  (make-account
    :id 3
    :balance 17.12))
(define a (make-account 3 17.12)) (def a (struct account 3 17.12)) (setq a
  (make-account :id 3 :balance 17.12))
struct getter
 
(account-id a) (account-id a) (:id a) (account-id a)
struct setter
 
(setf (account-balance a) 0) (set-account-balance! a 0) none (setf (account-balance a) 0)
struct predicate
 
(account-p a) (account? a) none (account-p a)
functions
common lisp racket clojure emacs lisp
let (let ((x 3) (y 4))
  (+ x y))
(let ((x 3) (y 4))
  (+ x y))
(let [x 3 y 4]
  (+ x y))
(let ((x 3) (y 4))
  (+ x y))
use lexical-let for lexical scope
let* (let* ((x 3) (y (* x x)))
  (+ x y))
(let* ((x 3) (y (* x x)))
  (+ x y))
(let [x 3 y (* x x)]
  (+ x y))
(let* ((x 3) (y (* x x)))
  (+ x y))
use lexical-let* for lexical scope
define function
 
(defun add (x y) (+ x y)) (define (add x y) (+ x y)) (defn add [x y] (+ x y)) (defun add (x y) (+ x y))
optional argument (defun add (a &optional b)
  (if (null b) a (+ a b)))
(define (add a (b null))
  (if (null? b) a (+ a b)))
(defn add ([a] a) ([a b] (+ a b)))
no syntax error if called with more than 2 args:
(defn add [a & [b]]
  (if (nil? b) a (+ a b)))
(defun add (a &optional b)
  (if (null b) a (+ a b)))
variable number of arguments (defun add (a &rest b)
  (if (null b)
    a
    (+ a (eval (cons '+ b)))))
(define (add a . b)
  (if (null? b)
    a
    (+ a (apply + b))))
(defn add [a & b]
  (if (nil? b) a (+ a (apply + b))))
(defun add (a &rest b)
  (if (null b)
    a
    (+ a (eval (cons '+ b)))))
default value (defun add (a &optional (b 0))
  (+ a b))
racket:
(define (add a (b 0)) (+ a b))
(defn add
  ([a] (add a 0))
  ([a b] (+ a b)))
none
named parameter (defun logarithm (&key number base)
  (/ (log number) (log base)))
 
(logarithm :base 2 :number 8)
none (defn logarithm [{x :number b :base}] (/ (Math/log x) (Math/log b)))
(logarithm {:base 2 :number 8})
(defun logarithm
  (&key number &key base)
  (if base
    (/ (log number) (log base))
    (log number)))
 
order significant, not key names:
(logarithm :foo 8 :bar 2)
return multiple values (defun sqrts (x)
  (values (sqrt x) (- (sqrt x))))
(define (sqrts x)
  (values (sqrt x) (- (sqrt x))))
(defn sqrts [x] (list (Math/sqrt x) (- (Math/sqrt x)))) values creates a list:
(defun sqrts (x)
  (values (sqrt x) (- (sqrt x))))
assign multiple values to local variables (multiple-value-bind (r1 r2)
  (sqrts 3)
  r2)
(let-values
  (((r1 r2) (sqrts 3)))
  r2)
(let [[r1 r2] (sqrts 3)] r2) (multiple-value-bind
  (r1 r2)
  (sqrts 3)
  r2)
assign multiple values to global variables (multiple-value-setq (r1 r2)
  (sqrts 3))
(define-values (r1 r2) (sqrts 3)) none (multiple-value-setq (r1 r2) (sqrts 3))
convert list to multiple values (values-list '(1 2 3)) (apply values '(1 2 3)) multiple values are lists multiple values are lists
assign multiple values to list (multiple-value-list (sqrts 3)) (call-with-values
  (lambda () (sqrts 3))
  list)
multiple values are lists multiple values are lists
tail call optimization yes for sbcl yes yes with recur no
lambda (lambda (x) (* x x)) (lambda (x) (* x x)) #(* % %)
(fn [x] (* x x))
(lambda (x) (* x x))
apply ((lambda (x) (* x x)) 2)
 
(apply #'(lambda (x) (* x x)) '(2))
((lambda (x) (* x x)) 2)
 
(apply (lambda (x) (* x x)) '(2))
(#(* % %) 2)
 
((fn [x] (* x x)) 2)
 
(apply #(* % %) '(2))
((lambda (x) (* x x)) 2)
 
(apply
  #'(lambda (x) (* x x))
  '(2))
get docstring
 
(describe #'mapcar) none (doc map) (describe-function 'mapcar)
define function with docstring (defun add (x y)
  "add x and y"
  (+ x y))
none (defn add "add x and y" [x y]
  (+ x y))
(defun add (x y)
  "add x and y"
  (+ x y))
apropos and documentation search none none (apropos #"^add$")
(find-doc #"add \S+ and \S+")
(apropos "^add$")
none
execution control
common lisp racket clojure emacs lisp
progn
 
progn prog1 prog2 begin none none
r6rs:
begin begin0 none
do none none progn prog1 prog2
loop (setq i 1)
(loop (print "hello")
  (if (> i 10)
    (return)
    (setq i (+ i 1))))
none, use recursion (loop [i 1]
  (if (<= i 10)
      (do (println "hello")
          (recur (+ i 1)))))
(setq i 1)
(loop (print "hello")
      (if (> i 10)
          (return)
          (setq i (+ i 1))))
do (do ((i 1) (sum 0))
  ((> i 100) sum)
  (setq sum (+ sum i))
  (setq i (+ i 1)))
do* initializes serially
none none (do ((i 1) (sum 0))
    ((> i 100) sum)
    (setq sum (+ sum i))
    (setq i (+ i 1)))
do* initializes sequentially
dotimes (dotimes (i 10 nil)
  (format t "hello~%"))
none (dotimes [_ 10]
  (println "hello"))
(dotimes (i 10 nil)
  (print "hello\n"))
if
 
(if (< x 0) (- x) x) (if (< x 0) (- x) x) (if (< x 0) (- x) x) (if (< x 0) (- x) x)
when (when (< x y)
  (print "x is less ")
  (print "than y"))
racket:
(when (< x y)
  (display "x is less ")
  (display "than y"))
(when (< x y)
  (println "x is less ")
  (println "than y"))
(when (< x y)
  (print "x is less ")
  (print "than y"))
cond (cond ((> x 0) 1)
  ((= x 0) 0)
  (t -1))
(cond ((> x 0) 1)
  ((= x 0) 0)
  (else -1))
(cond (> x 0) 1
  (= x 0) 0
  true -1)
(cond ((> x 0) 1)
  ((= x 0) 0)
  (t -1))
error
 
(error "failed") (error "failed") (throw (Exception. "failed")) (error "failed")
handle error (handler-case
  (error "failed")
  (simple-error (e)
    (format t "error: ~a" e)))
(with-handlers
  ((exn:fail?
     (lambda (e)
       (printf "error: ~a"
         (exn-message e)))))
  (error "failed"))
(try (throw (Exception. "failure"))
  (catch Exception e
    (printf "error: %s"
      (.getMessage e))))
(condition-case e
  (error "failed")
  (error (message "error: %s"
    (error-message-string e))))
define exception (define-condition odd-err (error)
  ((num :accessor odd-err-num
        :initarg :num))
  (:report
    (lambda (e s)
      (format s "odd number: ~a"
        (odd-err-num e)))))
(define exn:odd-err? "odd number") only symbols and keywords can be thrown and caught
throw exception (error 'odd-err :num 7) (raise exn:odd-err?) (throw (Exception. "failed")) (throw 'odd-err t)
catch exception (handler-case (/ 1 0)
  (division-by-zero ()
    (progn
      (format t "division by zero")
      nil)))
(with-handlers ((exn:fail? (lambda (e) (begin (printf "division by zero~n") null)))) (/ 1 0)) (try (/ 1 0) (catch ArithmeticException _ (do (println "division by zero") nil))) (catch 'failed (throw 'failed nil) t)
restart-case (defun halve (l)
  (mapcar (lambda (x)
    (restart-case
      (if (= (rem x 2) 0) (/ x 2)
        (error 'odd-error :num x))
      (round-down () (/ (- x 1) 2))
      (round-up () (/ (+ x 1) 2)))) l))
none none
invoke-restart (handler-bind
  ((odd-err
      (lambda (c)
        (invoke-restart
          'round-down))))
      (halve '(1 2 4 9)))
none none
finally clause (unwind-protect
  (error "failure")
  (print "clean up"))
none (try (throw (Exception. "failure"))
     (finally (println "clean up")))
(unwind-protect
  (error "failure")
  (print "clean up"))
lazy evaluation (define x (delay (/ 1 0)))
(promise? x)
(+ 1 (force x))
continuations (define cc null)
(+ 1 (call/cc (lambda (x) (set! cc x) 0)))
(cc 5)
create thread (.start (Thread. #(println "running…")))
wait on a thread (def t (Thread. #(Thread/sleep (* 30 1000))))
(.start t)
(.join t)
file handles
common lisp racket clojure emacs lisp
standard file handles *standard-input*
*standard-output*
*error-output*
end-of-file behavior read-line returns two values, the 2nd set to T at end-of-file.

EOF-OF-FILE is signaled when reading past end of file.
read line from stdin (setq line (read-line))
chomp
write line to stdout (defun println (s)
  (format t "~a~%" s))
 
(println "hello")
(define (println s)
  (printf "~a~n" s))

(println "hello")
(println "hello")
write formatted string to stdout (format t "~s ~d: ~2$~%"
  "foo"
  7
  13.7)
(printf "~a ~a: ~a~n"
  "foo"
  7
  (/ (round (* 13.7 100)) 100))
(printf "%s %d %.2f\n" "foo" 7 13.7)
open file for reading (setq in (open "/etc/hosts")) (define in (open-input-file "/etc/hosts")) (def in (java.io.BufferedReader. (java.io.FileReader. "/etc/hosts")))
open file for writing (setq out (open "/tmp/test" :direction :output :if-exists :supersede))
open file for appending (setq out (open "/tmp/test" :direction :output :if-exists :append))
close file
 
(close in) (close-input-port in) (.close in)
close file implicitly (with-open-file (out #P"/tmp/test" :direction :output) (write-line "lorem ipsum" out))
read line
 
(setq line (read-line in)) (define line (read-line in)) (def line (.readLine in))
iterate over file by line
read file into array of strings
read file into string
write string
write line
flush file handle
file buffers
emacs lisp
list buffers ;; list of buffer objects:
(buffer-list)

;; name of first buffer in list:
(buffer-name (car (buffer-list)))

;; name of current buffer:
(buffer-name (current-buffer))
current buffer
get and set
;; name of current buffer:
(buffer-name (current-buffer))

;; open in current pane:
(switch-to-buffer "foo.txt")

;; open in other pane:
(switch-to-buffer-other-window
  "bar.txt")
clear buffer ;; current buffer:
(erase-buffer)

;; buffer named "foo.txt:
(with-current-buffer "foo.txt"
  (erase-buffer))
point
get and set
;; 1-based index of char under cursor:
(point)

;; go to beginning of current buffer:
(goto-char 1)

;; go to end of current buffer:
(goto-char (buffer-size))
search and set point ;; Set point to character after string.
;; 1st arg is position in buffer beyond
;;   which search stops.
;; If 2nd arg is true, return nil
;;   on failure, otherwise raise error.
;; 3rd argument is the occurrence
;;   of the string, if negative
;;   search backwards from point.

(search-forward "lorem" nil t 1)
insert at string point ;; takes 1 or more args:
(insert "lorem" " ipsum")
current buffer as string (buffer-string)
insert file contents at point (insert-file "/etc/passwd")
mark
get and set
;; to beginning of current buffer:
(set-mark 1)

;; to point of current buffer:
(set-mark (point))
files
common lisp racket clojure emacs lisp
file test, regular file test (osicat:file-exists-p "/tmp/foo")
(osicat:regular-file-exists-p "/tmp/foo")
(file-exists-p "/etc/hosts")

(file-regular-p "/etc/hosts")
file size (eighth
  (file-attributes "/etc/hosts"))
is file readable, writable, executable
set file permissions (set-file-modes "/tmp/foo" #o755)
copy file, remove file, rename file (cl-fad:copy-file #P"/tmp/foo"
  #P"/tmp/bar")

(delete-file #P"/tmp/foo")

(rename-file #P"/tmp/bar"
  #P"/tmp/foo")
(copy-file "/tmp/foo" "/tmp/bar")
(delete-file "/tmp/foo")
(rename-file "/tmp/bar" "/tmp/foo")
create symlink, symlink test, get target (osicat:make-link "/tmp/hosts" :target "/etc/hosts") (make-symbolic-link "/etc/hosts" /tmp/hosts")

returns target if symlink or nil:
(file-symlink-p "/tmp/hosts")
temporary file (make-temp-file "foo")
in memory file (setq out (make-string-output-stream)

(write-string "lorem ipsum)

(get-output-stream-string out)

(setq in (make-string-input-stream "dolor sit amet"))

(read-line in)
directories
common lisp racket clojure emacs lisp
build pathname (make-pathname
  :directory '(:absolute "etc")
  :name "hosts")
dirname and basename (pathname-directory #P"/etc/hosts")

(pathname-name #P"/etc/hosts")
(file-name-directory "/etc/hosts")

(file-name-nondirectory
  "/etc/hosts")
absolute pathname (expand-file-name "..")
iterate over directory by file (dolist (file (osicat:list-directory "/tmp")) (format t "~a~%" file)) (dolist
  (file (directory-files "/etc"))
  (print file)))
make directory creates parents if 2nd arg non-nil:
(make-directory "/tmp/foo/bar" t)
recursive copy
remove empty directory (delete-directory "/tmp/foodir") (delete-directory "/tmp/foodir")
remove directory and contents (osicat:delete-directory-and-files "/tmp/foodir") (delete-directory "/tmp/foodir" t)
directory test (osicat:directory-exists-p #P"/etc") (file-directory-p "/etc")
processes and environment
common lisp racket clojure emacs lisp
external command (run-program "ls" '( "/etc")) (require scheme/system)
(system "ls /etc")
(.exec (Runtime/getRuntime) "ls") (shell-command "ls /etc")
backticks (shell-command-to-string "ls /etc")
command line arguments *posix-argv* current-command-line-arguments *command-line-args* in shebang mode only:
command-line-args or argv
environment variables (posix-getenv "HOME") (getenv "HOME") (System/getenv "HOME") (getenv "HOME")
libraries and namespaces
common lisp racket clojure emacs lisp
load a file
 
(load "a.lisp") (load "a.rkt") (load-file "a.clj") (load-file "a.el")
load a library
 
(require a) (require 'a) (load "a")
list installed packages, install a package (ql:quickload "osicat")
objects
common lisp racket clojure emacs lisp
define class (defclass rectangle ()
  (
    (height
      :accessor rectangle-height
      :initarg :height)
    (width
      :accessor rectangle-width
      :initarg :width)))
(define rectangle%
  (class object%
    (init width)
    (init height)
    (super-new)
    (define curr-height height)
    (define curr-width width)
    (define/public (get-height)
      curr-height)
    (define/public (get-width)
      curr-width)
    (define/public (set-height ht)
      (set! curr-height ht))
    (define/public (set-width wd)
      (set! curr-width wd))))
use java:
public class Rectangle {
  public float height;
  public float width;
  public Rectangle(float h, float w) {
    this.height = h;
    this.width = w;
  }
  public void setHeight(float h) {
    this.height = h;
  }
  public void setWidth(float w) {
    this.width = w;
}
make instance (make-instance 'rectangle
  :height 3
  :width 7)
(define rect
  (new rectangle
    (height 7)
    (width 3)))
(import 'Rectangle)
(def r (Rectangle. 7 3))
read attribute
 
(rectangle-height rect) (send rect get-height) (.height r)
write attribute
 
(setf (rectangle-height rect) 4) (send rect set-height 4) (.setHeight r 8)
define method (defmethod area ((figure rectangle))
  (* (rectangle-height figure)
    (rectangle-width figure)))
(define/public (area)
  (* curr-height curr-width))
(defmulti area class)
(defmethod area Rectangle [r] (* (.height r) (.width r)))
invoke method
 
(area rect) (send rect area) (area r)
universal superclass standard-object t object% Object
multiple inheritance yes no only one direct superclass; can implement multiple interfaces
macros
common lisp racket clojure emacs lisp
backquote and comma (setq op '+)
(eval `(,op 1 1))
(define op '+)
(eval `(,op 1 1))
(eval (quasiquote ((unquote op) 1 1)))
(def op +)
(eval `(,op 1 1))
(setq op '+)
(eval `(,op 1 1))
defmacro (defmacro rpn (arg1 arg2 op)
  (list op arg1 arg2))
(define-syntax-rule (rpn arg1 arg2 op) (op arg1 arg2)) (defmacro rpn [arg1 arg2 op]
  (list op arg1 arg2))
(defmacro rpn (arg1 arg2 op)
  (list op arg1 arg2))
defmacro w/ backquote (defmacro rpn (arg1 arg2 op)
  `(,op ,arg1 ,arg2))
(define-syntax-rule (rpn3 arg1 arg2 op)
  (eval ‘(,op ,arg1 ,arg2)))
(defmacro rpn [arg1 arg2 op] `(~op ~arg1 ~arg2)) (defmacro rpn (arg1 arg2 op)
  `(,op ,arg1 ,arg2))
macro predicate (macro-function rpn) none none none
macroexpand (macroexpand ’(rpn 1 2 +)) (syntax-object->datum (expand-to-top-form '(rpn 1 2 +))) (macroexpand '(rpn 1 2 +)) (macroexpand '(rpn 1 2 +))
splice quote (defmacro add ( &rest args )
  `(+ ,@args))
(define-syntax-rule ( add first …) (+ first …)) (defmacro add [ & args ] `(+ ~@args)) (defmacro add ( &rest args )
  `(+ ,@args))
recursive macro (defmacro add (a &rest b)
  `(if (null ',b)
    (+ ,a)
    (+ ,a (add ,@b))))
(define-syntax add (syntax-rules ()
  [(add x) x]
  [(add x y) (+ x y)]
  [(add x y …) (+ x (add y …))]))
(defmacro add ([a] `(+ ~a)) ([a & b] `(+ ~a (add ~@b)))) (defmacro add (a &rest b)
  `(if (null ',b)
    (+ ,a)
    (+ ,a (add ,@b))))
hygienic
 
no yes with # suffix no
local values (defmacro square-sum (x y)
  (let ((sum (gensym)))
    `(let ((,sum (+ ,x ,y)))
      (* ,sum ,sum))))
(define-syntax-rule (square-sum x y)
  (let ((sum (+ x y)))
    (* sum sum)))
(defmacro two-list [x] `(let [arg# ~x] (list arg# arg#))) (defmacro square-sum (x y)
  (let ((sum (gensym)))
    `(let ((,sum (+ ,x ,y)))
      (* ,sum ,sum))))
reflection
common lisp racket clojure emacs lisp
type-of
 
type-of none type class type-of
java interoperation
common lisp racket clojure emacs lisp
new (def rnd (new java.util.Random))
(def rnd (java.util.Random.))
method (. rnd nextFloat)
(.nextFloat rnd)
(. rnd nextInt 10)
(.nextInt rnd 10)
class method
 
(Math/sqrt 2)
chain
 
import (import '(java.util Random))
(def rnd (Random.))
to java array (to-array '(1 2 3))
(into-array Integer '(1 2 3))
__________________________________________ __________________________________________ __________________________________________ __________________________________________

General

version used

Versions used to verify data in the cheat sheet.

show version

How to determine the version.

Grammar and Invocation

compiler

racket

Compiling a.ss creates the byte-code compiled file a_ss.zo, which will be used by mzscheme in preference to the source code if it encounters

(require a)

making a standalone executable

common lisp

A standalone executable is created by the sb-ext:save-lisp-and-die function.

racket

In order for code to be compiled as a standalone executable, it must be packaged as a module. This can be accomplished by putting the #lang scheme shorthand the top of the file. All functions that are defined in the module will be executed in order. Here is a simple example:

#lang scheme
(define hello
  (printf "Hello world!~n"))

A standalone executable can be created with DrScheme using Scheme | Create Executable…

emacs

Building Emacs

shebang

How to have a script run by the interpreter automatically. Replace the given path with the path to the interpreter on your system.

emacs lisp

To run some lisp code from within emacs, use M-x load or M-x load-file. The first command will use the list of strings in load-path to search for the file. It is not necessary to specify the .el or .elc suffix if the file has one.

The following snippet is an emacs lisp shebang script implementation of cat:

#!/usr/bin/env emacs --script
(condition-case nil
  (let (line)
    (while (setq line (read-from-minibuffer ""))
        (princ line)
        (princ "\n")))
  (error nil))

An implementation of echo:

#!/usr/bin/env emacs --script
(condition-case nil
  (progn
    (dotimes (i (length argv) nil)
            (princ (nth i argv))
            (princ " "))
    (princ "\n"))
  (error nil))

repl

How to invoke the repl from the command line.

racket:

Racket also provides a GUI repl environment called DrRacket.

clojure:

The clojure repl saves the result of each evaluation in the variables *1, *2, … and the last exception in *e.

word separator

What is used to separate the operator and data of a S-expression.

are identifiers case sensitive?

Whether symbols are case sensitive. Common lisp is case insensitive, and as a result eq and EQ invoke the same function.

identifier characters

In lisps other than clojure, any character can be used in a symbol. Some characters are special to the reader and must be escaped to include them in a symbol. The reader will interpret a sequence of characters starting with a digit as a number instead of a symbol, so escaping must be used to create such a symbol.

common lisp:

Common Lisp is case insensitive, and the reader converts all letters to upper case. A symbol consisting of just periods "." must be escaped. Symbols that start and end with an asterisk "*" may conflict with system defined special variables.

racket:

# is only disallowed by the reader at the beginning of symbols. A symbol consisting of a single period must be escaped.

escaping characters in identifiers

How to escape characters which are special to the reader.

clojure:

Clojure does not have a mechanism for escaping special reader characters. As a result some characters cannot be used in a symbol.

quoting characters in identifiers

end-of-line comment

multiple line comment

#| |# delimited comments in Common Lisp and Scheme can span multiple lines, and thus can be used to comment out code.

clojure:

Code with balanced parens can be commented out in the following manner:

(comment
(+ 1 1)
)

Variables and Expressions

cell types

The different cell types. A lisp-1 only stores a single entity under a symbol in a given environment. A lisp-2 stores multiple entities, and which entity a symbol will resolve to depends on how the symbol is used. In particular, a value and a function can be stored under the same symbol without collision.

type predicates

Some basic data type predicates.

nil, is () null?, is () symbol?

(eq nil ())

is true in common lisp and emacs lisp.

(eq? () null)

is true in Scheme.

set property

How to associate additional data with a symbol. In the example, the symbol is foo, the property is :prop, and the value is 13.

**clojure:##

The properties associated with a symbol must be set when the value for the symbol is set.

get property

How to get the value of a property.

remove property

How to remove a property from a symbol.

quoted symbol

How to prevent the evaluation of a symbol.

keyword

Keywords are pre-defined symbols that evaluate to their printed representation. The reader recognizes them by the initial colon, or in the case of Scheme, by the initial "#:". In Scheme it is an error to use a keyword as an expression.

Ten Primitives

McCarthy introduced the ten primitives of lisp in 1960. All other pure lisp functions (i.e. all functions which don't do I/O or interact with the environment) can be implemented with these primitives. Thus, when implementing or porting lisp, these are the only functions which need to be implemented in a lower language. The way the non-primitives of lisp can be constructed from primitives is analogous to the way theorems can be proven from axioms in mathematics.

The primitives are: atom, quote, eq, car, cdr, cons, cond, lambda, label, apply.

One method of implementing logic and arithmetic with the ten primitives is Church encoding which represents natural numbers and logical values with lambda functions. Church numerals are not an efficient way to represent natural numbers; practical implementations implement arithmetic using underlying machine instructions.

atom

atom is is a predicate which returns false for cons cells, and true for anything else. All lists except for the empty list are cons cells.

racket

Scheme lacks atom, but cons? is its logical negation.

clojure

Clojure lacks cons cells. Thus atom if implemented in the language would always return true. However, (not (list? x)) is closer to the spirit and certainly more useful. Because nil is not the empty list in clojure there is also ambiguity about what the value of (atom ()) would be.

quote

All lisps have a single quote macro abbreviation for quote. Here are identical ways to quote a symbol and a list:

(quote a)
'a

(quote (+ 3 7))
'(+ 3 7)

eval is a one-sided inverse of quote. If X is arbitrary lisp code, then the following are identical

X
(eval (quote X))

eq, equal, =

In his 1960 paper, McCarthy described eq as undefined if either or both arguments are not atomic. Common Lisp and Scheme (eq?) return true if the arguments both evaluate to the same list in memory, otherwise false. equal and equal? (Scheme) return true if the arguments evaluate to lists with the same elements as determined by calling equal or equal? recursively.

In Common Lisp and Scheme, = can only be called on numeric arguments. The predicates for whether a symbol is numeric are numberp and number?, respectively.

Clojure dispenses with eq and equal and defines = to be equivalent to the Common Lisp equal.

car

Because car and cdr are abbreviations for parts of the word of the IBM 704, there is a trend to replace them with first and rest. However, car and cdr are short, and convenient notation exists for abbreviating nested calls to car and cdr.

In terms of car, cdr, and combinations thereof, here is what the dialects define:

common lisp r5rs racket clojure emacs lisp
car,first car car,first first car,first
cadr,second cadr cadr,second second,fnext cadr,second
caddr,third caddr caddr,third caddr,third
cadddr,fourth cadddr cadddr,fourth cadddr,fourth
fifth fifth fifth
sixth sixth sixth
seventh seventh seventh
eighth eighth eighth
ninth ninth ninth
tenth tenth tenth
cdr, rest cdr cdr, rest rest,next cdr, rest
cddr cddr cddr cddr
cdddr cdddr cdddr cdddr
cddddr cddddr cddddr cddddr
caar caar caar ffirst caar
cdar cdar cdar nfirst cdar

cdr

common lisp

cdr and rest return nil when called on an empty list.

racket

cdr and rest raise an error when called on an empty list.

clojure

rest returns an empty set () when called on an empty or singleton list, whereas next returns nil. In clojure, the empty set evaluates as true in a boolean context and nil evaluates as false.

cons

clojure

Clojure does not implement a list as a linked list of cons cells. The second argument to cons must be a list.

cond

lambda

clojure:

(#(+ %1 %2) 1 2)

label

apply

Arithmetic and Logic

true and false

Literals for true and false.

falsehoods

Values which evaluate to false in a boolean context.

common lisp

nil and the empty list () are identical.

racket

The empty list does not evaluate as false in a boolean context. There is no predefined symbol nil.

clojure

nil evaluates as false in a boolean context, but is not identical as the empty list.

emacs lisp

nil and empty list () are identical.

is true a symbol?

logical operators

The logical operators.

relational operators

Relational operators for performing comparisons.

min and max

Functions for returning the least and greatest of the arguments.

numeric predicates

A selection of numeric predicates.

realp and real? are true of all numbers which have a zero imaginary component. floatp and inexact? are true if the number is being stored in a floating point representation.

racket:

The following all evaluate as #t:

(rational? 1.1)
(rational? (sqrt 2))
(rational? pi)

closure of integers under division

The number system that containing the potential results of integer division. In mathematics, the closure of integers under division is the rationals, and this is true for common lisp, scheme, and clojure as well.

Emacs lisp performs integer division (i.e. computes the quotient), so the closure of the integers under division is the integers.

arithmetic operators

In Lisp, + and * take zero or more arguments and - and / take one or more arguments. With zero arguments + and * return the additive and multiplicative identities 0 and 1. With one argument + and * return the argument and - and / return the additive and multiplicative inverses: i.e. the negation and the reciprocal. When evaluating 3 or more arguments - and / are computed from left to right: i.e. (- 3 4 5) is computed as (- (- 3 4) 5).

clojure:

Math.pow returns a double.

emacs:

Unary division (i.e. computing the reciprocal) generates a wrong number of arguments error.

transcendental functions

float truncation

For rounding, floor, and ceiling, the return value is integer if the argument is rational and floating point if the argument is floating point, unless otherwise noted.

racket:

inexact->exact can be used to convert a float returned by round, ceiling, or floor to an integer.

clojure:

Math/round always returns an integer and throws and error if called on a rational. Math/floor and Math/ceil can be called on a rational, but always return a float.

emacs:

round, ceiling, and floor return integers. fround, fceiling, and ffloor return floats.

quotient and remainder

(sqrt -2)

The value of (sqrt -2). Common lisp and Scheme support complex numbers. Clojure and Emacs Lisp do not.

decomposition of integer, rational, complex

For absolute value, the type of the return value is the same of the type of the argument.

racket:

The scheme/math library must be loaded to use sgn.

clojure:

Math/signum only operates on a float and returns a float

random number

How to generate a random integer, and a random float in a uniform and a normal distribution.

bit operators

racket:

The bitwise operators implemented by Gambit and Racket are specified in the withdrawn standard SRFI 33.

emacs:

Also has ash, which gives a different value when both arguments are negative.

Strings

character literals

The syntax for character literals. The first literal uses the letter "a" as an example of how to write a literal for all ASCII printing characters.

common lisp:

Characters are of type standard-char. The predicate is characterp.

racket:

The predicate is char?.

clojure:

Characters are of type java.lang.Character.

emacs:

Characters are of type integer and can be manipulated by arithmetic operators. characterp and integerp are synonyms.

string literal

The syntax for a string literal.

string escapes

A list of escape sequences that can be used in string literals.

emacs lisp:

The \x escape sequence is followed by one to six hex digits. Because a variable number of hex digits can be used, it may be necessary to indicate the end of the sequence with a backslash and a space, e.g. the following string literal is "λ123":

  "\x3bb\ 123"

character access

How to get the character at a given position in a string.

find substring

Find the location of a substring in a string.

extract substring

length

constructors

comparison

common lisp:

Here is the complete list of string comparison functions:

string=
string<
string>
string<=
string>=
string/=

There are also case insensitive versions of the above functions:

string-equal
string-lessp
string-greaterp
string-not-greaterp
string-not-lessp
string-not-equal

racket:

Case sensitive string comparison:

string<=?
string<?
string=?
string>=?
string>?

Case insensitive string comparison:

string-ci<=?
string-ci<?
string-ci=?
string-ci>=?
string-ci>?

emacs lisp:

Emacs has only these string comparison functions, all of which are case sensitive:

string=
string-equal
string<
string-lessp

string= and string-equal are synonyms, as are string< and string-lessp.

case

trim

emacs:

An implementation of trim:

(defun trim (s)
  (let ((s1 (replace-regexp-in-string "[ \t]*$" "" s)))
    (replace-regexp-in-string "^[ \t]*" "" s1)))

convert from string, to string

How to convert strings to numbers, and numbers to strings.

common lisp:

read-from-string invokes the reader, so the return value is not guaranteed to be a floating point number.

Here is a parse-float function which will convert all real numeric types to floats and raise a simple error if another condition is encountered.

(defun parse-float (s)
  (let ((readval (handler-case
                  (read-from-string s)
                  (sb-int:simple-reader-error nil)
                  (end-of-file nil))))
    (cond ((realp readval ) (+ readval 0.0))
          (t (error (concatenate 'string "not a float: " s))))))

concat

split

join

format

regular expressions

common lisp

http://weitz.de/cl-ppcre/

emacs lisp

string-match returns the first index of the first matching substring, or nil.

The following code moves the point to next position following the point that matches the argument, and returns the index of the that position.

(re-search-forward "hello")

regex substitution

regex special characters

Lists

list literal

pair literal

(car '())

(cdr '())

(eval '())

A practical advantage of having (eval '()) be equal to '() is that the empty list doesn't have to be quoted.

list functions

nth

nth and list-ref count from zero. nth returns nil if the index is too large. list-ref throws an error.

index of list element

How to get the index of a list element. The first element of a list has an index of zero.

last butlast

In clojure, last and butlast are analogs of first and rest which operate at the end of a list. If X is a list, then the following code pairs are identities:

(last X)
(first (reverse X))

(butlast X)
(reverse (rest (reverse X)))

The analogy breaks down in Common Lisp because last returns a list with a single element.

set-car set-cdr

common lisp:

The following code pairs perform the same operation on the list:

(setf (car l) 3)
(rplaca l 3)

(setf (cdr l) '(4 5 6))
(rplacd l '(4 5 6))

However, they are not identical because rplaca and rplacd return the modified list instead of their 2nd argument.

racket:

Racket provides a separate interpreter plt-r5rs for an R5RS compliant version of Scheme. Also, the language can be set to R5RS within DrRacket.

emacs lisp:

Also has setf.

sort

assoc

clojure

In Clojure, assoc returns a new association with the specified values replaced:

(def numbers {1 :one 2 :two 3 :three 4 :four})
(def jumble (assoc numbers 1 :uno 3 :drei 4 :quatre))

getf

racket:

How to implement getf in Scheme:

(define (getf lst key (default null))
    (cond ((null? lst) default)
          ((null? (cdr lst)) default)
          ((eq? (car lst) key) (cadr lst))
          (else (getf (cddr lst) key default))))

map

common lisp

The lambda can accept multiple arguments:

(mapcar '+ '(1 2 3) '(4 5 6))

racket

(map + '(1 2 3) '(4 5 6))

clojure

(map + '(1 2 3) '(4 5 6))

emacs lisp

mapcar does not accept multiple argument lambdas

filter

common lisp

Also the negative version:

(remove-if (lambda (x) (> x 2)) '(1 2 3))

clojure

Also the negative version:

(remove #(> % 2) '(1 2 3))

emacs lisp

Also has negative version:

(remove-if (λ (x) (> x 2)) '(1 2 3))

reduce (left fold)

right fold

clojure:

How to define foldr:

(defn foldr [f init list] (reduce #(f %2 %1) (reverse list)))

sublis

How to apply the mapping defined by an associative list to a recursive list.

dolist

take

Here is how to define take for common lisp or emacs lisp:

(defun take (n l)
  (cond ((< n 0) (error "index negative"))
        ((= n 0) ())
        ((null l) (error "index too large"))
        (t (cons (car l) (take (- n 1) (cdr l))))))

drop

push and pop

racket:

Here is an implementation of push and pop in Racket using boxes:

(define (push x a-list)
  (set-box! a-list (cons x (unbox a-list))))

(define (pop a-list)
  (let ((result (first (unbox a-list))))
    (set-box! a-list (rest (unbox a-list)))
    result))

clojure:

Note the in clojure, pop only returns the first element; the original list is left unmodified.

Arrays

vector literal

racket

#(1 2 3) creates an immutable vect. (vector 1 2 3) creates a mutable vector.

vector access

set vector element

racket

vector-set! throws an error if called on an immutable vector.

vector to list

list to vector

abstract sequence

Lists and vectors support the same operations; the only difference is the speed at which the operations can be performed. It is a convenience for the developer if functions that perform the operations have the same name; i.e. if lists and vectors are members of an abstract sequence type. Clojure has gone furthest in this direction, making all the customary list functions work on vectors as well. In common lisp and emacs lisp, some of the list functions also work on vectors, and some don't. In Scheme none of the list functions work on vectors.

sequence data types

The containers that respond to sequence functions.

sequence predicate

list functions usable on sequences

make-array

In Lisp terminology, both arrays and vectors refer to collections which are of fixed size; vectors are arrays with rank 1. Only common lisp supports arrays with rank greater than 1.

array access

set array element

array dimensions

array-rank returns the number of indices required to specify an element in the array. array-dimensions returns the size of the array; the number of cells is the product of the elements of the list.

range

list comprehension

Dictionaries

make hash

racket

Use the following to get access to the hash functions:

(require scheme/dict)

put hash

Put a key/value pair in a hash.

clojure

The hash map is immutable. The assoc function returns a new version of the hash with the additional key/value pairs provided as arguments.

get-hash

Lookup a value in a hash by key.

hash key not found

racket:

Racket throws and error when the key is not found. Here is how to handle the error and return a null when the key is not found:

(with-handlers ((exn:fail? (lambda (e) null))) (get h "goodbye"))

rem-hash

hash size

map hash

defstruct

struct

struct getter

struct setter

struct predicate

Functions

let, let*

Traditionally let performs its assignments in parallel and let* serially.

clojure

In Clojure, let and let* are synonyms and both perform serial assignment.

emacs

Note that let uses dynamic scope. Use lexical-let for lexical scope:

ELISP> (let ((x 3)) (defun get-x () x))
get-x
ELISP> (get-x)
*** Eval error ***  Symbol's value as variable is void: x
ELISP> (let ((x 4)) (get-x))
4
ELISP> (lexical-let ((x 3)) (defun get-x-2 () x))
get-x-2
ELISP> (get-x-2)
3
ELISP> (lexical-let ((x 4)) (get-x-2))
3

define function

optional argument

variable number of arguments

default value

named parameter

common lisp:

In common lisp, named parameters are optional. Named values can be assigned default values:

 (defun logarithm (&key number (base 10)) (/ (log number) (log base)))

If a named parameter is not provided at invocation and has not been assigned a default value, then it is set to nil.

racket:

How to Implement Named Parameters in Scheme

emacs lisp:

In emacs lisp named parameters are mandatory. A runtime error results in they are not provided when the function is invoked.

tail call optimization

common lisp:

The ANSI Common Lisp specification does not require an implementation to perform tail call optimization.

get docstring

How to get the documentation string for a function.

common lisp:

describe returns the documentation string with additional information such as the function signature. To get just the documentation string use this:

(documentation #'mapcar 'function)

define function with docstring

How to define a function that has a documentation string.

apropos and documentation search

How to search definitions and documentation.

Apropos takes a pattern and returns all defined symbol names which match the pattern.

clojure:

apropos returns matching symbol names as a list.

find-doc searches all documentation strings and writes any which match to standard out.

Both apropos and find-doc can take a string or a regular expression as an argument.

emacs lisp:

apropos displays the documentation for matching definitions in the *Apropos* buffer. The argument is a string but will be treated as a regular expression.

Execution Control

progn

progn and its equivalents in other dialects returns the value of the last expression. Common Lisp and Emacs Lisp also have prog1 and prog2 for returning the value of the 1st or 2nd expression.

loop

do

dotimes

if

when

error

handle error

racket:

Calling error raises an exception of type exn:fail

emacs:

In the example:

(condition-case nil (error "failed") (error (message "caught error") nil))

the 2nd argument to condition-case is the code which might raise an error, and the 3rd argument is the error handler. The error handler starts with condition to be caught. The last nil is the return value of the entire condition-case expression.

An error cannot be handled by catch. An uncaught throw will generate an error, which can be handled by a condition-case error handler.

define exception

How to define a custom exception with a payload.

common lisp:

The :report clause is not necessary. If defined it will be displayed if the exception is handled by the lisp debugger.

throw exception

emacs:

The 1st argument of an emacs throw expression identifies the type of exception, and the 2nd argument will be the return value of the catch expression that catches the exception.

catch exception

emacs

The following catch expression will return nil:

(catch 'failed (throw 'failed nil) t)

restart case

invoke restart

finally clause

racket:

clojure:

Here is an optional technique for making sure that a file handle is closed:

(with-open [#^PrintWriter w (writer f)] (.print w content))

lazy evaluation

continuations

create thread

wait on thread

File Handles

standard file handles

end-of-file behavior

read line from stdin

chomp

write line to stdout

write formatted string to stdout

racket

printf prints to stdout. format returns a string.

emacs lisp

The format statement returns the generated string. When used for i/o, it prints in the emacs minibuffer.

open file for reading

open file for writing

open file for appending

close file

close file implicitly

read line

iterate over file by line

read file into array of strings

read file into string

write string

write line

flush filehandle

File Buffers

Files

file test, regular file test

file size

is file readable, writable, executable

set file permissions

copy file, remove file, rename file

create symlink, symlink test, get target

temporary file

in memory file

Directories

build pathname

How to build a file pathname from components.

dirname and basename

How to extract the directory portion of a pathname; how to extract the non-directory portion.

absolute pathname

How to get the get the absolute pathname for a pathname. If the pathname is relative the current working directory will be appended.

iterate over a directory by file

How to iterate over the files in a directory.

make directory

How to create a directory, including any parents directories specified in the path.

recursive copy

How to copy a directory and its contents.

remove empty directory

How to remove an empty directory.

remove directory and its contents

How to remove a directory and its contents.

directory test

How to test whether a directory exists.

Processes and Environment

external command

command line arguments

emacs

The global variables command-line-args and argv are set when emacs is run in shebang mode: i.e. with the —script option. command-line-args contains the pathname used to invoke emacs, as well as any options processed by emacs at startup, in addition to any additional arguments. argv only contains the additional arguments.

environment variables

Libraries and Namespaces

loading a file

How to load a file and evaluate the top level expressions.

common lisp

Does not display the result of any evaluations.

racket

Displays the result of the last evaluation.

loading a library

Objects

define class

make instance

read attribute

write attribute

define method

invoke method

define subclass

universal superclass

multiple inheritance

Macros

backquote and comma

defmacro

defmacro-backquote

macro predicate

macroexpand

macroexpand recursively expands a sexp until the head is no longer a macro. It does not expand arguments that are macros.

common lisp

Common lisp also has macroexpand-1, which will non-recursively expand a macro once. The head of the expansion may thus be a macro.

clojure

Clojure also has macroexpand-1. See above for an example of use.

emacs lisp

Emacs has macroexpand-all, which will recursively expand a sexp until head and arguments are free of macros.

splice quote

recursive macro

hygienic

Does the language have macros whose expansions are guaranteed not to introduce name collisions.

local values

Reflection

type-of

How to get the data type of the entity referred to by a symbol.

Java Interoperation

version used on jvm

extra libraries used

racket:

The srfi-1 library brings in a common list functions which Kawa does not make available by default. See SRFI.

new

method

class method

chain

import

to java array

Common Lisp

ANSI Specification
Common Lisp: The Language 2nd Ed. gizpped download
SBCL User Manual
CLISP Man Page
CLiki: Common Lisp Wiki
Practical Common Lisp Seibel
ASDF Manual
Quicklisp

Common Lisp was designed by committee. The initial standard was agreed upon in 1983, and the Common Lisp Object System (CLOS) was added in 1988. Common Lisp became an ANSI standard in 1994.

To test examples in the reference sheet we are using SBCL (Steel Bank Common Lisp) which is fast and feature complete. The only potential downside to SBCL is that the Windows port is considered experimental. CLISP, by contrast, is easy to install and works well on Windows.

For a package manager we use Quicklisp. It works with SBCL and CLISP. Here is how to install it and use it to load the cl-ppcre library:

$ curl -O http://beta.quicklisp.org/quicklisp.lisp
$ sbcl
* (load "quicklisp.lisp")
* (quicklisp-quickstart:install)
* (ql:quickload "cl-ppcre")
* (cl-ppcre:all-matches "foo" "foo bar")

Quicklisp creates a quicklisp directory in the user's home directory. Once quicklisp is downloaded and installed, it can be used like this:

$ sbcl
* (load "~/quicklisp/setup.lisp")
* (ql:quickload "cl-ppcre")
* (cl-ppcre:all-matches "foo" "foo bar")

When using SBCL we can ensure that Quicklisp is automatically loaded at startup by putting the load command into the .sbclrc file:

$ cat ~/.sbclrc
(load "~/quicklisp/setup.lisp")

Racket

R5RS
R6RS
Guide: Racket
Reference: Racket
Gambit Documentation
Kawa Language Framework
Scheme Requests for Implementation (SRFI)
Scheme Links
Scheme Now
Chicken Scheme
Chicken Egg Index
MIT Scheme Reference

Scheme as a dialect of Lisp is characterized by lexical scope, mandatory tail call optimization, and first class continuations.

The R5RS standard (1998) added hygienic macros to the language. In all standards up to and including R5RS the standards body focused on defining a small core of features. The result was a language ideal for instruction or academic experimentation. The R6RS standard (2007) by contrast defined support for libraries, modules, networking, and Unicode. Most Scheme implementations only aim to be R5RS compliant. Racket is the only implementation which has implemented a significant portion of the R6RS features.

Because of the inconsistent adoption of R6RS, a universal package manager for all Scheme implementations is a difficult undertaking. Scheme Now (Snow) is an effort in this direction, but the package manager snowman doesn't work with Racket, Gambit, or Kawa, the implementations used in this reference sheet.

A process was initiated in 1998 called Scheme Request For Implementation (SRFI) which develops specifications for Scheme standard libraries. As of 2010 74 of the specifications have achieved a final status. Here is a page showing which SRFIs have been implemented for which Scheme implementations.

Racket ships with a large number of libraries in the collects directory of the installation which can be loaded with the require command, which takes a raw symbol which is the relative pathname from the collects directory to the file, not including the .rkt suffix. The Racket 5.1 distribution includes 50 SRFI libraries.

Racket also has a built in package management system. Browse the list of available packages. To install a package, click through to the detail page for the package and get the require string to load it. If the require string is executed by Racket, the library will be downloaded somewhere in the user's home directory. When I ran this on my Mac

$ racket
> (require (planet "spgsql.rkt" ("schematics" "spgsql.plt" 2 3)))

the files for the PostgreSQL database bindings were installed in ~/Library/Racket.

Chicken Scheme packages are called eggs. Use the command line utility chicken-install to install an egg. The egg can be loaded in the interpreter with the use commnad:

$ sudo chicken-install srfi-19
$ csi
#;1> (use srfi-19)
#;2> (define d (make-date 0 0 0 0 9 7 2011))
#;3> (leap-year? d)
#f

Clojure

Clojure Reference
Java 1.6 API

Calling Java

Here are the basics of calling Java code:

(def rnd (new java.util.Random))  ; create Java object
(. rnd nextFloat)  ; invoke method on object
(. rnd nextInt 10)  ; invoke method with argument
(. Math PI)  ; static member
(import '(java.util Random))  ; import

Clojure automatically imports everything in java.lang.

There are shortcuts for the above syntax:

(Random.)
(new Random)

Math/PI
(. Math PI)

(.nextInt rnd)
(. rnd nextInt)

Because they are primitive types and not objects, Clojure provides functions specific to Java arrays:

(make-array CLASS LEN)
(make-array CLASS DIM & DIMS)
(aset ARY IDX VAL)
(aset ARY IDX_DIM1 IDX_DIM2 ... VAL)
(aget ARY IDX)
(aget ARY IDX_DIM1 IDX_DIM2 ...)
(alength JARY)
(to-array SEQ)
(into-array TYPE SEQ)
(amap ARY I COPY EXPR)
(areduce ARY IDX  COPY INIT EXPR )

Emacs Lisp

GNU Emacs Manual
GNU Emacs Lisp Reference Manual

To get an introduction to Emacs Lisp Programming from within Emacs use

  C-h i m Emacs Lisp Intro

Run M-x lisp-interaction-mode to put Emacs in lisp interaction mode. In lisp interaction mode the command C-x e will evaluate the s-expression on the current line. M-x eval-buffer will evaluate the entire buffer.

Use lisp interaction mode to define functions which can be called from Emacs. The following defines a function called dired-emacs-lisp for browsing the Emacs Lisp directory:

(defun dired-emacs-lisp ()
  "Open the Emacs Lisp directory in dired."
  (interactive)
   (dired "/Applications/Emacs.app/Contents/Resources/lisp"))

The directory is hard-coded into the function and may be different on your system. Once defined the function can be invoked with M-x dired-emacs-lisp. Not all Lisp functions can be called in this manner. Those that can are called commands. The body of a command has an optional documentation string, followed by a call to interactive, followed by the code which executes when the command is invoked. The documentation string can be accessed from Emacs by running M-x describe-function and entering the name of the function when prompted.

The call to interactive is what makes a Lisp function a command. It can takes optional arguments. Use M-x describe-function on interactive to see a description of these arguments.

To bind the command to the key C-c l run the following in Lisp interaction mode:

(global-set-key "\C-cl" 'dired-emacs-lisp)

If it is desired to have the above command and key binding always available when Emacs starts up, put them in ~/.emacs.d/init.el.

content of this page licensed under creative commons attribution-sharealike 3.0