Clojure Quick Reference

8/13/2019 Clojure Quick Reference

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Clojure quick reference

Having recently started using Clojure(a great language), I find myself missing an easier way

to look up which operations are available.

he official core !"I referencelists them all, but scanning a list of hundreds of names # plus

other references for special forms, reader macrosand $ava interop# is either hit or miss or

re%uires more patience than I usually have.

&o here is a %uick reference to all core operations # core !"I, special forms, reader macros

and $ava interop # in Clojure '..

Clojure '. is not yet released at the time of this writing, there may be differences in the final

version.

his page is a work in progress, and may include mistakes. here are no guarantees ofsuitability for any particular purpose, etc. etc. )

jf, July 2010

Update

he new community#driven documentation site clojuredocs.orgis impressive, even at the

tender age of two weeks, and looks likely to make this document unnecessary.

his document will remain online, but there will probably be no more revisions. ! semi#official community site like Clojure*ocs has a much better chance of +dotting all the is+ and

keeping the documentation up to date.

hanks to -achary im for the Clojure*ocs initiative.

jf

v. 0.86, 2010-07-23

revision history

Version numbers reflect aro!imate comleteness of this "ocumento 1.0 #oul" be $100% comlete

&ll core functions, secial forms etc. are liste"

o 'ot all of them have "escritions an" e!amles

(roof-rea"in) is still en"in)

*or a +lojure tutorial, see +lojure - functional ro)rammin) on the JV

in"ly hoste" by 000#ebhost.com

Table of Contents

Clojure data types

'
http://clojure.org/http://clojure.github.com/clojure/clojure.core-api.htmlhttp://clojure.org/special_formshttp://clojure.org/special_formshttp://clojure.org/readerhttp://clojure.org/java_interophttp://clojuredocs.org/http://clojuredocs.org/http://faustus.webatu.com/clj-quick-ref.html#revisionshttp://java.ociweb.com/mark/clojure/article.htmlhttp://www.000webhost.com/http://faustus.webatu.com/clj-quick-ref.html#clojure-data-typeshttp://clojure.org/http://clojure.github.com/clojure/clojure.core-api.htmlhttp://clojure.org/special_formshttp://clojure.org/readerhttp://clojure.org/java_interophttp://clojuredocs.org/http://faustus.webatu.com/clj-quick-ref.html#revisionshttp://java.ociweb.com/mark/clojure/article.htmlhttp://www.000webhost.com/http://faustus.webatu.com/clj-quick-ref.html#clojure-data-types


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o /eneral

&imple values

o 0oolean

o 1umber

o &ymbol and keyword

o &tring and charactero 2egular e3pressions

Collections and se%uences

o 4ector

o 5ist

o 6ap

o &et

o &truct

o &e%uence

o ransient

7unctionso 6ultifunctions

o 6acros

$ava data types

o $ava objects

o $ava arrays

o $ava primitives

o ype hints

o $ava pro3ies

o Clojure in $ava

8perations

o 7low controlo ype inspection

o Concurrency

Code structure

o 4ariables

o 0indings

o 1amespaces

o Hierarchies

o 9ser#defined types

o Comments and documentation

o 6etadata :nvironment

o 2e%uire;use;import

o Code

o I8

o 2:"5

o 6isc.

&elected libraries

Clojure data types

Clojure relates to these primary data types
http://faustus.webatu.com/clj-quick-ref.html#generalhttp://faustus.webatu.com/clj-quick-ref.html#simple-valueshttp://faustus.webatu.com/clj-quick-ref.html#booleanhttp://faustus.webatu.com/clj-quick-ref.html#numberhttp://faustus.webatu.com/clj-quick-ref.html#symbol-and-keywordhttp://faustus.webatu.com/clj-quick-ref.html#string-and-characterhttp://faustus.webatu.com/clj-quick-ref.html#regular-expressionshttp://faustus.webatu.com/clj-quick-ref.html#collections-and-sequhttp://faustus.webatu.com/clj-quick-ref.html#vectorhttp://faustus.webatu.com/clj-quick-ref.html#listhttp://faustus.webatu.com/clj-quick-ref.html#maphttp://faustus.webatu.com/clj-quick-ref.html#sethttp://faustus.webatu.com/clj-quick-ref.html#structhttp://faustus.webatu.com/clj-quick-ref.html#sequencehttp://faustus.webatu.com/clj-quick-ref.html#transienthttp://faustus.webatu.com/clj-quick-ref.html#functionshttp://faustus.webatu.com/clj-quick-ref.html#multifunctionshttp://faustus.webatu.com/clj-quick-ref.html#macroshttp://faustus.webatu.com/clj-quick-ref.html#java-data-typeshttp://faustus.webatu.com/clj-quick-ref.html#java-objectshttp://faustus.webatu.com/clj-quick-ref.html#java-arrayshttp://faustus.webatu.com/clj-quick-ref.html#java-primitiveshttp://faustus.webatu.com/clj-quick-ref.html#type-hintshttp://faustus.webatu.com/clj-quick-ref.html#java-proxieshttp://faustus.webatu.com/clj-quick-ref.html#clojure-in-javahttp://faustus.webatu.com/clj-quick-ref.html#operationshttp://faustus.webatu.com/clj-quick-ref.html#flow-controlhttp://faustus.webatu.com/clj-quick-ref.html#type-inspectionhttp://faustus.webatu.com/clj-quick-ref.html#concurrencyhttp://faustus.webatu.com/clj-quick-ref.html#code-structurehttp://faustus.webatu.com/clj-quick-ref.html#variableshttp://faustus.webatu.com/clj-quick-ref.html#bindingshttp://faustus.webatu.com/clj-quick-ref.html#namespaceshttp://faustus.webatu.com/clj-quick-ref.html#hierarchieshttp://faustus.webatu.com/clj-quick-ref.html#user-defined-typeshttp://faustus.webatu.com/clj-quick-ref.html#comments-and-documenhttp://faustus.webatu.com/clj-quick-ref.html#metadatahttp://faustus.webatu.com/clj-quick-ref.html#environmenthttp://faustus.webatu.com/clj-quick-ref.html#require-use-importhttp://faustus.webatu.com/clj-quick-ref.html#codehttp://faustus.webatu.com/clj-quick-ref.html#iohttp://faustus.webatu.com/clj-quick-ref.html#replhttp://faustus.webatu.com/clj-quick-ref.html#mischttp://faustus.webatu.com/clj-quick-ref.html#mischttp://faustus.webatu.com/clj-quick-ref.html#selected-librarieshttp://faustus.webatu.com/clj-quick-ref.html#generalhttp://faustus.webatu.com/clj-quick-ref.html#simple-valueshttp://faustus.webatu.com/clj-quick-ref.html#booleanhttp://faustus.webatu.com/clj-quick-ref.html#numberhttp://faustus.webatu.com/clj-quick-ref.html#symbol-and-keywordhttp://faustus.webatu.com/clj-quick-ref.html#string-and-characterhttp://faustus.webatu.com/clj-quick-ref.html#regular-expressionshttp://faustus.webatu.com/clj-quick-ref.html#collections-and-sequhttp://faustus.webatu.com/clj-quick-ref.html#vectorhttp://faustus.webatu.com/clj-quick-ref.html#listhttp://faustus.webatu.com/clj-quick-ref.html#maphttp://faustus.webatu.com/clj-quick-ref.html#sethttp://faustus.webatu.com/clj-quick-ref.html#structhttp://faustus.webatu.com/clj-quick-ref.html#sequencehttp://faustus.webatu.com/clj-quick-ref.html#transienthttp://faustus.webatu.com/clj-quick-ref.html#functionshttp://faustus.webatu.com/clj-quick-ref.html#multifunctionshttp://faustus.webatu.com/clj-quick-ref.html#macroshttp://faustus.webatu.com/clj-quick-ref.html#java-data-typeshttp://faustus.webatu.com/clj-quick-ref.html#java-objectshttp://faustus.webatu.com/clj-quick-ref.html#java-arrayshttp://faustus.webatu.com/clj-quick-ref.html#java-primitiveshttp://faustus.webatu.com/clj-quick-ref.html#type-hintshttp://faustus.webatu.com/clj-quick-ref.html#java-proxieshttp://faustus.webatu.com/clj-quick-ref.html#clojure-in-javahttp://faustus.webatu.com/clj-quick-ref.html#operationshttp://faustus.webatu.com/clj-quick-ref.html#flow-controlhttp://faustus.webatu.com/clj-quick-ref.html#type-inspectionhttp://faustus.webatu.com/clj-quick-ref.html#concurrencyhttp://faustus.webatu.com/clj-quick-ref.html#code-structurehttp://faustus.webatu.com/clj-quick-ref.html#variableshttp://faustus.webatu.com/clj-quick-ref.html#bindingshttp://faustus.webatu.com/clj-quick-ref.html#namespaceshttp://faustus.webatu.com/clj-quick-ref.html#hierarchieshttp://faustus.webatu.com/clj-quick-ref.html#user-defined-typeshttp://faustus.webatu.com/clj-quick-ref.html#comments-and-documenhttp://faustus.webatu.com/clj-quick-ref.html#metadatahttp://faustus.webatu.com/clj-quick-ref.html#environmenthttp://faustus.webatu.com/clj-quick-ref.html#require-use-importhttp://faustus.webatu.com/clj-quick-ref.html#codehttp://faustus.webatu.com/clj-quick-ref.html#iohttp://faustus.webatu.com/clj-quick-ref.html#replhttp://faustus.webatu.com/clj-quick-ref.html#mischttp://faustus.webatu.com/clj-quick-ref.html#selected-libraries


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&imple values

o 0ooleans

o 1umbers

o &ymbols and keywords

o &trings and characters

o 2egular e3pressions Collections

o 4ector

o 5ist

o &et

o 6ap

o &truct

o &e%uence

7unctions

&ee clojure.or) "ata structures

General

hese operations apply to all values.

nil 5iteral +nothing+. !s $ava null. nil => nil

nil< rue if value is nil. (nil? 0) => false

= >v ? vs@

rue if one or more values are e%ual.

Aorks on most Clojure data types

including nested lists and maps.9ses .e%uals for $ava objects.

Collection comparison ignores

collection type, but separates

se%uential (list, vector, se%) and

associative (map) types.

(= 1) => true (= 1 1.0 1e0) =>true (= () []) => true (= [] {})=> false (= [1] (seq '(1))) =>true (= nil nil) => true

not= rue if two values are not e%ual. (not= :a :b) => true

%uote

urns off evaluation for what follows

the %uote.

'a => a a => Excetion: !annotresol"e a '(# 1 $) => (# 1 $) (# 1$) => %

compare >a

b@

Compare two values to find which is

greater. B, B= etc. is reserved fornumbers, this is for comparing non#

numeric values.

2eturns

B if a B b

D if a D b

if a = b.

Aorks for types that implement$ava

Comparable!mong Clojure native

types, this is

boolean

(co&are true false) => 1 (co&are1 $) => 1 (co&are b a) => 1(co&are foo bar) => *(co&are 'x '+) => 1 (co&are:x :x) => 0 (co&are [1 $] [1 %])=> 1 (co&are '(1) '($)) =>Excetion: !annot cast to!o&arable

E
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number

symbol

keyword

char

string

vector of the above

comparator

>pred@

2eturns a comparator based on a

predicate pred.

"red is an fn along the lines of +greater

than+ or +smaller than+. It must accept

two arguments, the two items to

compare, and return logical true if the

first argument is smaller (or greater)

and logical false otherwise.

he return function implements

java.util.Comparator.

(,ef lt (co&arator -)) (lt 1 $)=> 1 (lt $ 1) => 1 re, forseq. co&arison (,efn seqlttrue if seq a - seq b [a b](ne/? (co&are ("ec a) ("ecb)))) co&are seqs (,ef seqco&(co&arator seqlt)) (seqco&'(1) '($)) => 1 (seqco& '($)'(1)) => 1

identical true(i,entical? (nte/er. 1) (nte/er.1)) => false

hash Hash value of argument (as [1]) => %$

Simple values8perations for simple native data types like boolean and string.

Boolean

he values nil and false are treated as false in logical tests, any other value is considered true.

(Including the empty list, which is considered false in many other 5isps.) his is called

+logical truth+.

he function booleanconverts from Clojure logical truth to boolean true and false, primarily

for $ava interop.he functions true? false?tests for boolean true or false.

true

false0oolean literals true => true

and >?

args@

akes Fero or more args, evaluates args in

order. ! nil or false will short#circuit

evaluation. 2eturns the last value evaluated.

In effect 2eturns logical true if all the args are

logical true, logical false otherwise.

Can be used to test#and#get in one e3pression

(an, :a :b :c) => :c (an, nil:b) => nil (an, false :b) =>false (an,) => true

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(an, ar/ (./et2a&e ar/))returns nil if the

argument is nil and the name otherwise, saving

a separate test for nil.

or >?

args@

akes Fero or more args, evaluates args in

order. ! logical true (non#nil and non#false)value will short#circuit evaluation. 2eturns the

last value evaluated.

In effect 2eturns logical false if all the args

are logical false, logical true otherwise.

Can be used to get a default value

(or sulie,"al ,efault"al)returns

the supplied value if there is one (i.e. not nil),

and the default value otherwise.

(or :a :b :c) => :a (ornil :b) => :b (or false nil)=> nil (or nil false) =>false (or) => nil

not >arg@2eturns boolean true if arg is nil or false,

boolean false otherwise.(not nil) => true

booleanConverts arg to boolean. 7alse and nil is false,

anything else is true.

(boolean nil) => false(boolean 0) => true (boolean()) => true

true 13*

.G6 decimal ($ava 0ig*ecimal) $.*4 => $.*4

'e' float, scientific notation 1e1 => 10.0

L


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#'.'e#'

':'

' integer, octal notation 015 => 16

377 3ff integer, he3 notation 0xff => $66

r''

'Jr77

EJrMN-

integer, custom base #EJ.

7ormat base O +r+ O value.

*igits D K are represented as upper# or lower#

case letters # a=', b=''... F=EL.

*igit D= base is an error.

$r101 => 6 %7r89=> **0$5

rit!metic

O

#

P

;

1ote Integer division that does

not give an integer result is

returned as a 2atio.

(3 1$ %) => * (3 $ 1.1) => 1.;1...(3 1% %) => 1%3%

%uotInteger divison returning an

integer, truncating any remainder.(quot $7 7) => *

rem

mod

2emainder and modulo, the

integer remainder after integer

division. 2em and mod are the

same e3cept when used with

negative numbers.

(re& 1% %) => 1 (re& 1% %) => 1(&o, 1% %) => $

inc >i@

dec >i@Increase or decrease arg with one. (inc 1) => $ (,ec 1.1) => 0.1

ma3 >? args@

min >? args@

2eturns the highest or lowest

number among arguments (&ax 1 7.7 %) => 7.7

with#precision

>prec ? e3prs@

with#precision

>precrounding

mode ?

e3prs@

"recision and optional rounding

mode for 0ig*ecimal operations.

2e%uired for results that cannot be

represented in 0ig*ecimal.

2ounding modes

C:I5I1/

75882 H!57Q9"

H!57Q*8A1

H!57Q:4:1

9"

*8A1

911:C:&&!2N

&ee $ava 0ig*ecimal

(3 14 *) => 0.$64 (3 14 %) =>0.%%4 (itrecision 10 (3 14 %))=> 0.%%%%%%%%%%4

rand 2andom float .#'. (ran,) => 0.6;5...

rand#int >n@ 2andom int >, n)(ran,int 10) => %

unchecked#inc 7aster versions of the standard (uncece,,ec 1) => 0 (uncece,,ec 1.0) =>

J
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#dec

#add

#subtract

#divide

#multiply#negate

#remainder

ops. Int only, dont check for

overflow, dont do type

conversions.

lle/altrue(- 1 * 6 10)=> true

==:%uality for numbers. Aorks only for numbers, returns false for any

other comparison. "resumably slightly faster than normal e%uality.

(== 1 1.0) =>true(== true true)=> false

Bit operations

0it operations work with integers (byte short int long 0igInteger) only.

bit#and >a b@ 5ogical !1* on bits in args. (bitan, 1 %) => 1

bit#and#not 5ogical 1!1*(bitan,not 1 %) => $

bit#or 5ogical 82 (bitor 1 %) => %

bit#3or 5ogical M82 (either bit set, but not both) (bitxor 1 %) => $

bit#flip >3 n@ 7lip bit at inde3 n(bitfli 1 %$) =>*$*75$5

bit#notConverts ' to and to ' up to the highest

non#Fero bit.(bitnot %) => *

bit#clear >3 n@ &et bit at inde3 n to (bitclear % 0) => $

bit#set >3 n@ &et bit at inde3 n to ' (bitset $ 0) => %

bit#shift#left >3

n@&hifts bits n positions left (bitsiftleft $ 1) => *

bit#shift#right &hift bits n positions right(bitsiftri/t $ 1) =>1

bit#test >3 n@ rue if bit at inde3 n is ' (bittest $ 1) => true

Casts

byte short int long float

double bigint bigdec

Coerce arg to the

specified $ava type.

!rg will wrap if too big to

fit in the type.

(b+te 1$5) => 1$5 (b+te 1$;) =>1$; (b+te $67) => 0

num Coerce to a number ??rationaliFe Convert a float to a ratio (rationali@e 1.1) => 11310


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numerator

denominator

1umerator or

denominator of a ratio.(nu&erator (3 % *)) => %

Tests

number< true if arg is a number(nu&ber? 1.14) => true(nu&ber? 1) => false(nu&ber? 1) => false

integer false(inte/er? 1.1) => false(inte/er? (b+te 1)) => true

float false (float?1.1) => true

decimal< rue if arg is $ava 0ig*ecimal.(,eci&al? 1.1) => false(,eci&al? 1.14) => true

ratio< rue if arg is ratio.(ratio? 1.1) => false (ratio?1) => false (ratio? 13%) =>true

even"alue [1 $]

print#str

println#str

!s print and println, but prints to string. Inserts a

space between each arg. println adds a newline at

the end.

(rintstr 1 abc) => 1abc

pr#str

prn#str

!s pr and prn, but prints to string.

9nlike print, pr prints in a form Clojure can read

in again.

(rstr 1 abc) =>1 abc

with#out#

str

2edirects standard out (PoutP) to a string which is

returned at the end. Convenient for capturing print

output when you need it as a string.

(itoutstr (rintln 1abc)) => 1 abcn

char#

escape#

string

2eturns escape string for representing char in a

string, or nil if none.

(carescaestrin/ a)=> nil (carescaestrin/ ) =>

char#name#

string

2eturns char name for named chars (the specialunprintable ones).

(carna&estrin/ a) =>nil (carna&estrin/sace) => sace

Use

count >s@ 5ength of string (count abc) => %

get >s i@ Char at inde3 i (/et abc 0) => a

subs >s i#

from@

subs >s i#

from i#to@

&ubstring between start inde3 (inclusive) and end of

string, or between start inde3 and end inde3

(e3clusive).

(subs abc 1) => bc(subs abc 1 $) => b

(subs abc 1 1) =>

K
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format 7ormats a string using synta3 ofjava.util.7ormatter.(for&at B,B0$,B0$,$000 1 1) => $0000101

Casts and tests

char >n@ Convert int to char. (car 10) => neline

char true

#egular e$pressions

Create

S+..+5iteral rege3 pattern. 9ses $ava rege3

synta3

C[a@]s#

re#pattern

Creates rege3 pattern from string. 1ote the

e3tra backslash escape re%uired by $ava

strings wo backslashes in the string to

produce one in the rege3p.

(reattern [a@]s#) =>C[a@]s#

re#

matcher

>r3 s@

2eturns ajava.util.rege3.6atcherfor rege3

on string.

(re&atcer CaD aba) =>C-a"a.util.re/ex.4atcer>

Use

re#find >r3

s@

re#find

>m@

7inds the first match within the string. If no

groups, returns a string, otherwise a vector where

the first element is the full match and the rest are

the groups.

!rguments are either a rege3p and a string or a

java.util.rege3p.6atcher.

(refin, Cc baa) =>nil (refin, Ca# baa)=> aa (refin, Cb(a#)baab) => [baa aa]

re#

matches

>r3 s@

ries to match the entire string. 2eturn value as

for re#find.

(re&atces Ca# baa)=> nil (re&atcesCb(a#) baa) => [baaaa]

re#se% >r3s@ 2eturns a se%uence of all matches in string.

(reseq Cb(a#) babaa)

=> ([ba a] [baaaa])

re#groups

>m@

!ccepts a matcher, returns the last groups

matched.

Test

here is no standard Clojure test for whether a value is a rege3, but you can make your own

(,efn re/ex? ["] (instance? a"a.util.re/ex.Fattern "))

Collections and sequences

'
http://java.sun.com/javase/6/docs/api/java/util/Formatter.htmlhttp://java.sun.com/javase/6/docs/api/java/util/Formatter.htmlhttp://java.sun.com/javase/6/docs/api/java/util/regex/Pattern.htmlhttp://java.sun.com/javase/6/docs/api/java/util/regex/Pattern.htmlhttp://java.sun.com/javase/6/docs/api/java/util/regex/Matcher.htmlhttp://java.sun.com/javase/6/docs/api/java/util/Formatter.htmlhttp://java.sun.com/javase/6/docs/api/java/util/regex/Pattern.htmlhttp://java.sun.com/javase/6/docs/api/java/util/regex/Pattern.htmlhttp://java.sun.com/javase/6/docs/api/java/util/regex/Matcher.html


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Clojure has five primary collection types 4ector, list, set, map and struct.

In addition there is se%uencewhich may be thought of as an iterator interface.

8perations listed under each collection type are either particular to the type (like assoc for

maps) or the bare minimum re%uired to use the type.

he bulk of operations are on se%uences, and se%uence operations can be used on allcollection types.

In addition to the primary types there are some special cases

Sorted sets and maps%eeps their entries sorted on value (sets) or key (maps).

&ersistent vs transient collections%"ersistent collections are the default, they are

immutable. ransient collections are currently an e3perimental feature that allows

mutation. (6utation is always possible by using $ava types instead.)

'perations

count

>coll@

2eturns the number of

entries # the siFe or

length.

/ives eternal loop for

infinite se%s.

(count [1 [$ %]]) => $

empty

>coll@

:mpty collection of

same category as coll,

or nil.

(e&t+ nil) => nil (e&t+ [1]) => [] (e&t+'(1)) => () (e&t+ {:a 1}) => {} (e&t+ (seq {:a1})) => ()

not#empty

>coll@

1il if coll is empty,

otherwise coll(note&t+ []) => nil (note&t+ [1]) => [1]

into >to#

coll from#

coll@

Collection to#coll with

all elements in from#

coll added.

2eturn collection will

be the same type as

to#coll.

(into '(1) [$ %]) => (% $ 1) (into [1] '($ %))=> [1 $ %] (into {:a 1} {:b $}) => {:a 1 :b $}(into C{:a} C{:b :c}) => C{:a :b :c} (into (seq[1]) [$ %]) => (% $ 1)

conj >c ?

elms@

2eturns collection

with one or more

values added.

2eturn collection will

be the same type as

the argument.

(con [1] $ %) => [1 $ %] (con '(1) $ %) => (%$ 1) (con {:a 1} [:b $]) => {:a 1 :b $} (conC{:a} :b) => C{:a :b} (con (seq [1]) $ %) => (%

$ 1)

Content tests

containsc key@

! strange one

rue if c is a set and contains

key.

rue if c is a map or struct and

contains key.

rue if c is a vector and containskey as in"e!

(contains? C{:a :b} :a) => true GH(contains? {:a 1} :a) => true GH(contains? [*$ *%] *$) => false ?(contains? [*$ *%] 0) => true &atcon in,ex (contains? '(1 $ %) 1) =>false ??

''
http://faustus.webatu.com/clj-quick-ref.html#sequencehttp://faustus.webatu.com/clj-quick-ref.html#sequencehttp://faustus.webatu.com/clj-quick-ref.html#sequence


12/66

7alse for lists and se%uences.

/ives somewhat unintuitive

results if used by name alone. If

looking for a value, use some.

distinctcoll@

rue if all elements in coll aredistinct (non#e%ual)

(,istinct? [1 $ %]) => true

emptycoll@

rue if arg is nil or empty

collection, string, array or

se%uence.

(e&t+? nil) => true (e&t+? ()) =>true (e&t+? {}) => true (e&t+? ) =>true (e&t+? (intarra+ 0)) => true

every< >f

se%@

rue if f, a '#arg function, returns

logical true for every element in

se% or collection.

(e"er+? C(- B 6) [1 $ 7]) => false(e"er+? C(- B 10) [1 $ 7]) => true

not#everyf se%@

he inverse of every< # true if f

returns logical false for any

element in se% or coll.

(note"er+? C(- B 6) [1 $ 7]) => true

some >f

se%@

5ogical true if f returns logical

true for an element in se%, nil

otherwise.

he lack of a %uestion mark (i.e.

some rather than some true (so&eC(> B 10) [1 $ 7]) => nil (so&ei,entit+ [nil :a nil]) => :a

not#any< >f

se%@

he inverse of some.

rue if f returns logical false for

every element in se%.

(notan+? C(- B 6) [1 $ 7]) => false

Capability tests

Capability tests are often better to use than type tests, as data can come wrapped in several

different collection types.

ype tests should be reserved for the cases where you need a specific type due to program

logic or performance # like a vector for random access and inde3 calcuations.

se%uential< rue for se%uential types # vectors,lists and se%uences.(sequential? [1 $]) => true(sequential? {:a 1} => false

associative true(associati"e? '(1 $)) => false

sorted false (sorte,?(sorte,set 1 $)) => true

counted< rue if coll supports count (gettingthe length) in constant time

(counte,? [1]) => true (counte,? (seq[1])) => false

'


13/66


14/66

args@ ("ector 1 $ %) => [1 $ %]

vector#of

>type@

Creates new vector to store a primitive type.

type is boolean, char etc.

!s a standard vector, but stores primitive

values internally.

6ore space efficient when storing manyprimitives.

(con ("ectorof :int) 1)=> [1]

Use

conj >v ? elms@2eturns vector with one or more values appended

at end.

(con [1] $ %) => [1$ %]

peek >v@2eturns last element.

lastworks too, but peek is faster.(ee [1 $]) => $

pop >v@2eturns vector with last element removed.

butlastworks too, but pop is faster.

(o [1 $]) => [1]

get >v i@

(>..@ i)

2eturns element at inde3 i.

ntworks too, but these are faster.

(/et [1 $] 0) => 1([1 $] 0) => 1

assoc >v i e@

2eturns new vector where elm at inde3 i is

replaced with e.

i must be within vector siFe bounds.

(assoc [1 $] 0 10)=> [10 $]

subvec >v i#

from@

subvec >v i#from

i#to@

&ubvector from i#from (inclusive) to i#to

(e3clusive) or to end of vector.

:fficient, shares structure with the original.

(sub"ec [1 $] 1) =>[$](sub"ec [1 $] 0 1)=> [1]

rse% >v@ 2eturns a se% of items in vector v in reverse order.

!lso works for sorted maps.

(rseq [1 $ %]) => (%$ 1)

List

5inked lists.

Cheap !dding and removing on the front, iterating # con cons o first next rest

:3pensive 2andom access # nt

Create

(..) 5iteral list '(a $ %) => (a $ %)

list >?

items@

Creates a list containing the items.

9nlike the literal list, arguments are

evaluated before insertion.

(list a $ %) => Excetion: !annotresol"e a (list 1 $ %) => (1 $ %)

listP >?

items@

Creates a list containing the

arguments.

he last argument is a se%uence that

the other values are prepended to.

(listD 1 $ [% *]) => (1 $ % *)

'G


15/66

Use

conj

>list

elm@

!dds element to start of list.

conj also is used for vectors, but will there add

the element at the end.

(con '($ %) 1) => (1 $ %)

peek>list@

2eturns the first element. (ee '($ %)) => $

pop

>list@2eturns the list with the first element removed. (o '($ %)) => (%)

first

>list@2eturns the first element. (first '($ %)) => $

rest

>list@

2eturns rest of the list, or an empty list when

there are no more items. 2est on empty list or

nil returns empty list.

(rest '($ %)) => (%) (rest'(%) => () (rest ()) => ()(rest nil) => ()

nth >list

n@

2eturns the nth element in the list. 7irst

element is inde3 .(nt '(1 $) 1) => $

)ap

! map stores a mapping from a key to a value. !ny value can be used as key or value,

including nil.

Create

T..U

5iteral map.

Commas between key;value pairsare optional.

{:a 1 :b $ :c %}{nil 0K :a 1K :b $}

hash#map >?

kvs@

Creates a map from argument list,

where every two elements are key

and value.

(as&a :a 1 :b $) => {:a 1 :b $}

array#map >?

kvs@

!s hash#map, but uses an array

implementation that retains the

order of the arguments.

5inear lookup time, only suitable

for small maps.

8rdering may be lost when

appended to (assoc).

(arra+&a :b 1 :a $) => {:b 1 :a$}

Fipmap >keys

vals@

!s hash#map, but takes two se%s

of keys and values, mapping the

first key to the first value etc. until

the end of either the keys or

values.

(@i&a [:a :b] [1 $]) => {:a 1 :b$}

sorted#map >?

keyvals@

sorted#map#by

>comp ?

keyvals@

Creates a map kept sorted by keys,

keys will remain sorted through

inserts (assoc) and deletes

(dissoc).

sorted#map#by takes a comparatorto supply the ordering.

(sorte,&a :b 1 :a $) => {:a $K :b1} (sorte,&ab+ (co&arator -)$ :x 1 :+) {1 :+K $ :x}

'L


16/66

bean >o@

Creates a map from a $ava0ean

object.

I.e. return values from no#arg

methods on the form getMyF() are

mapped to keys on the form 3yF

(bean a"a.at.!olor3LEM){:transarenc+ 1K :re, $66K :/reen0K :class a"a.at.!olorK :blue0K :ala $66K :LNO 766%7}

fre%uencies

>coll@

2eturns a map with each elementin coll mapped to the element

count.

(frequencies (seq abbc)) => {a 1b $ c 1}

Use

assoc >map ?

keyvals@

2eturns a map with the new

mapping k v. If mapping e3ists,

the old value is replaced.

(assoc {:a 1} :b $) => {:a 1 :b $}(assoc {:a 1 :b 1} :b $) => {:a 1 :b$} (assoc {:a 1} :b $ :c %) => {:a 1:b $ :c %}

assoc#in >map>k ? ks@ v@

!dds a new mapping to a nested

map.>k ? ks@ is a se%uence of keys.

(associn {:a {:b $}} [:a :b] %) =>{:a {:b %}}

dissoc >m ?

keys@

2emoves the mapping for the

specified key or keys.

(,issoc {:a 1 :b $} :a) => {:b $}(,issoc {:a 1 :b $ :c %} :a :b) =>{:c %}

find >m key@2eturns the map entry for key,

or nil if none.(fin, {:a 1 :b $} :a) => [:a 1]

key

val

2eturns the key and value of a

map entry

(e+ (fin, {:a 1} :a)) => :a ("al(fin, {:a 1} :a)) => 1

keys

vals

2eturns a se%uence of all keys

or values in the map.

(e+s {:a 1 :b $}) => (:a :b) ("als{:a 1 :b $}) => (1 $)

get >m key@

(m key)

(key m)

2eturns the value for the key ornil if none.

he map itself can be used as

the function with the key as

argument.

If the key is a keyword, the key

can be used as the function with

the map as argument.

9se /etif the map might be nil

and you dont want an

e3ception.

(/et {:a 1 :b $} :a) => 1 (/et {:a 1:b $} :c) => nil ({:a 1 :b $} :a) =>1 (:a {:a 1 :b $}) => 1

get#in >m >key

? ks@@

2eturns the value from a nested

map, where key ? ks is a

se%uence of keys.

(/etin {:a {:b $}} [:a :b]) => $

update#in >m

>key ? keys@ f

? args)

9pdates a value in a nested

map.

f is a function that will take the

old value plus args and return

the new value.

(u,atein {:a {:b $}} [:a :b] # )=> {:a {:b 11}}

select#keys >m

keyse%@

2eturns a map containing only

the keys listed

(selecte+s {:a 1 :b $ :c %} [:a:c] ) => {:c %K :a 1}

merge >m ?maps@

6erges two or more maps.If there are duplicate keys the

(&er/e {:a 1 :b $} {:c % :b 1000} )=> {:a 1 :c % :b 1000}

'J


17/66

last value (going left to right) is

used.

merge#with >f

? maps@

!s merge, but if there are

duplicate keys both values are

passed to f which returns the

new value.

(&er/eit # {:a 1 :b $} {:a $ :b%} ) => {:a % :b 6}

Use sorted

hese operations are for sorted maps.

rse% >m@

2eturns a se% of items in sorted#

map m in reverse order.

!lso works for vectors.

(rseq (sorte,&a :a 1 :b $))=> ([:b $] [:a 1])

subse% >m t v@subse% >m t#from v#

from t#to v#to@

2eturns a subse%uence of items in

sorted#map m.t is a test function, it must be one

of B, B=, D and D=.

v is the value to compare keys

against.

rsubse% >m t v@

rsubse% >m t#from v#

from t#to v#to@

!s subse%, but returns the items in

reverse order.

Set

! set stores a collection of distinct (non#e%ual) values. !ny value can be stored, including nil.

$ava types must implement .as!o,e() and .equals(Gbect) according to their

respective contracts in the $ava !"I.

Create

ST..U

5iteral set.

Can hold any type of

value including nil.

C{eter aul &ar+}

hash#set >?vals@

Creates empty hash set orset containing vals.

(asset) => C{} (asset nil :a :b)=> C{nil :a :b}

set >coll@Creates set from distinct

elements in coll.(set [1 $ 1]) => C{1 $}

sorted#set >?

vals@

sorted#set#by

>comp ? vals@

Creates a sorted set.

8ptionally supply a

comparator for the sorting.

(sorte,set % $ 1) => C{1 $ %} (sorte,setb+ (co&arator >) 1 $ %) => C{% $ 1}

Use

conj >s Conjoin !dds value(s) to set (con C{} :a :b) => C{:a :b}

'
http://java.sun.com/j2se/1.4.2/docs/api/java/lang/Object.html#hashCode()http://java.sun.com/j2se/1.4.2/docs/api/java/lang/Object.html#hashCode()http://java.sun.com/j2se/1.4.2/docs/api/java/lang/Object.html#equals(java.lang.Object)http://java.sun.com/j2se/1.4.2/docs/api/java/lang/Object.html#equals(java.lang.Object)http://java.sun.com/j2se/1.4.2/docs/api/java/lang/Object.html#hashCode()http://java.sun.com/j2se/1.4.2/docs/api/java/lang/Object.html#equals(java.lang.Object)


18/66

? vals@

disj >s ?

vals@*isjoin 2emoves value(s) from set (,is C{:a :b} :a) => C{:b}

get >set

val@(ST...U

val)

(key

ST...U)

5ook up value in set. 2eturns value or nil if

not present.

!s for maps, using get and using the set asthe function are e%uivalent. If values are

keywords the keyword can be used as the

lookup function.

/etdoes not throw e3ception if the set is

nil.

(/et C{1 $ %} 1) => 1 (C{1 $ %}%) => % (:eter C{:&ar+ :eter})=> :eter (:aul C{:&ar+:eter}) => nil

Struct

&tructs can be considered special#purpose hash maps with a fi3ed set of keys, midway

between a map and an object.

&tructs are used to store multi#segment fi3ed#format values, like "erson.

! struct#map is a map e3tending a struct type, where the keys;fields from the struct type are

given but more keys can be added as needed.

/tructs are "erecate" in +lojure 1.2, "efrecor" is referre".

Create

defstruct >name

? keys@

Creates a named struct type with the given

fields. &ame as (,ef na&e (createstructe+s))

(,efstruct erson:na&e :a/e)

create#struct >?

keys@Creates a struct type with the given fields.

(,ef erson (createstruct :na&e :a/e))

struct >stype ?

vals@

Creates a struct of stype with the given values.

4alues must be in the same order as the keys

in the type.

(struct erson on10) => {:na&e on:a/e 10}

struct#map

>stype ? init#vals@

Creates a struct map from the supplied struct

type and a list of initial values.

accessor >stype

field@

2eturns a function that takes a struct instance

and returns the value of the field. &lightly

more efficient than using get.

Use

get >s key@

(s key)

(key s)

4alue for the struct key.

!s for maps.

(let [ (struct erson on 10) ] (/et :na&e)) => on

assoc >s key 2eturns a new struct with the (let [ (struct erson on 10)] (assoc :na&e &ar+)) => {:na&e &ar+ :a/e

'


19/66

value@new key;value mapping.

!s for maps.10}

Sequence

&e%uence is an interface roughly analogous to $avas Iterator It is a small interface (a couple

of methods) that can be applied to a large range of data types. 6any (most


20/66

Create

se% >arg@

Create a se% from the argument.

!rg can be collection, string, $ava array (including

primitive arrays) and anything implementing

Iterable.&e% on empty coll or nil returns nil.

(seq [1 $]) => (1 $)(seq {:a 1 :b $}) =>([:a 1] [:b $]) (seq {})=> nil (seq nil) => nil

se%uence

>coll@

Creates a se% from the coll.

!s se%, e3cept that se% returns nil on empty coll or

nil, while se%uence returns an empty se%.

(sequence [1 $]) => (1$) (sequence {}) => ()(sequence nil) => ()

repeat >3@

repeat >n 3@Creates a laFy se% with n or infinite copies of 3

(reeat % :a) => (:a:a :a)

replicate >n

3@

Creates a laFy se% with n copies of 3.

7rom before reeatgot an optional n argument.

(relicate % :a) =>(:a :a :a)

range >@

range >nto@range

>nfrom nto@

range

>nfrom nto

nstep@

2eturns a laFy se% of ints in range nfrom

(inclusive) to nto (e3clusive).

If no args, nfrom is , nstep is ' and nto is infinity.

(ran/e %) => (0 1 $)(ran/e 1 6 $) => (1 %)

repeatedly

>f@

repeatedly

>n f@

2eturns a laFy se% of n or infinite calls to f,

presumably for side effects. 7 takes no arguments.

1ote that the se% is laFy, so nothing is printed until

the se% is consumed. f might for instance print out

the variables in a loop, by consuming one element

per iteration you would get the current value of thevars.

(reeate,l+ % C(rintPiQ)) =>PiQPiQPiQ

iterate >f 3@2eturns a laFy se% of 3, (f 3), (f (f 3)) etc.

f must take one arg and not have side effects.

(tae % (iterate C(D $B) $)) => ($ * ;)

laFy#se% >?

body@

2eturns a laFy se% that will evaluate the body

when called, caching the result.

he e3ample uses print since we need a printout to

see when things happen.

18: his is an infinite se%, dont print. 9se

first;ne3t;take to e3tract a few values.

(,efn counter [i] counts la@il+ fro& ito infinit+ (rint i is i ) (consi (la@+seq (counter (inc i))))) (,eft& (counter 0)) => i is 0 firstrint (first t&) => 0 first "alue(secon, t&) => i is 1 secon, rint=> 1 secon, "alue (tae % t&) => iis $ => (0 1 $) to cace,K one ne"alue

laFy#cat >?

colls@

5aFy concatenation of all colls.

:3ample shows 7ibonacci numbers. ! laFy#cat is


21/66

stored in var fibsbut no values are e3tracted yet.

he initial laFiness is needed to delay evaluation of

the fibs argument to map until after the var has

been defined.

2emaining laFiness comes from map, it will onlyevaluate as much as it is asked for.

(,ef fibs (la@+cat [1 1] (&a # fibs(rest fibs)))) (tae ; fibs) => (1 1 $ %6 ; 1% $1)

Create from e$isting

cycle >coll@5aFy infinite cycle of elements

in coll.(tae 6 (c+cle [1 $])) => (1 $ 1 $ 1)

interleave >c'c ? more@

5aFy se% of first item in eachcoll, second item etc.

(interlea"e [1 %] [$ *]) => (1 $ % *)

interpose >sep

coll@

5aFy se% of inserting sep

between each element of coll.(interose 0 [1 $ %]) => (1 0 $ 0 %)

tree#se% >tree f#

branch< f#

children root@

5aFy se% of tree nodes.

tree is a nested se%uence.

f#branch< accepts a node and

returns true if node may have

children.

f#children accepts a node and

returns its children.root is root of tree.

3ml#se% 5aFy tree se% of 3ml nodes

enumeration#

se%

5aFy se% from $ava

:numeration

iterator#se% 5aFy se% from $ava Iterator

file#se% >dir@5aFy tree se% of java.io.7iles.

!rg is a directory.

(,ef f (fileseq (a"a.io.Rile.3usr))) (tae % f) => (C-Rile 3usr>C-Rile 3usr3bin> C-Rile3usr3bin3$to%>)

line#se%

>reader@

5aFy se% of lines from reader,

a java.io.0uffered2eader

his is an e3ample using only

clojure core and $ava. In

practice, you may want to use

duck#streamsfrom

clojure.contrib.

(i&ort '[a"a.io RilenutStrea&nutStrea&Lea,er Ouffere,Lea,er])(itoen [r, (> (RilenutStrea&.3etc3osts) (nutStrea&Lea,er.)(Ouffere,Lea,er.)) ] (rintln (first(,ro 7 (lineseq r,))))) =>1$5.0.0.1 localost

resultset#se%

>rs@

5aFy se% of structmaps for

rows in java.s%l.2esult&et

Use + general

sort >se%@ &ort se%uence. 8ptionally use (sort [$ 1]) => (1 $) (sort > [1 $]) =>

'
http://richhickey.github.com/clojure-contrib/duck-streams-api.htmlhttp://richhickey.github.com/clojure-contrib/duck-streams-api.html


22/66

sort >comp

se%@supplied comparator. ($ 1)

sort#by

>key#f se%@

sort#by

>key#f compse%@

!s sort, but key#f is used to

e3tract the value to sort on

from each element.

8ptionally use suppliedcomparator.

(sortb+ C(first B) [[$ :a] [1 :b]] ) =>([1 :b] [$ :a]) (sortb+ C(first B) >

[[1 :a] [$ :b]] ) => ([$ :b] [1 :a])

reverse returns a reverse se%uence (re"erse [1 $ %]) => (% $ 1)

flatten

returns a flattened se%uece #

elements are kept, nested

se%uences removed

(flatten [1 [$]]) => (1 $)

Use + access

first

secondlast

first, second and last element of

se%uence

(first '(1 $)) => 1 (secon, '(1 $)]

=> $ (last '(1 $ %)] => %

rest

he rest of se%, after the first.

2eturns empty se% when no more

elements or arg is nil.

(rest '(1 $)) => ($) (rest '($)) =>() (rest '()) => () (rest nil) => ()

ne3t

!s rest, but returns nil at end of

se%.

&ee clojure.org discussion of rest

vs. ne3t

(next '(1 $)) => ($) (next '($)) =>nil (next '()) => nil (next nil) =>nil

ffirst !s (first (first 3)) (ffirst '((1 $) % *)) => 1

nfirst !s (ne3t (first 3)) (nfirst '((1 $) % *)) => ($)

fne3t !s (first (ne3t 3)) (fnext '((1 $) % *)) => %

nne3t !s (ne3t (ne3t 3)) (nnext '((1 $) % *)) => (*)

nth >coll n@ 2eturns the nth element. (nt '(1 $) 0) => 1

nthne3t

>coll n@

2eturns the nth ne3t, as calling

ne3t n times in a row.(ntnext '(1 $ %) $) => (%)

rand#nth

>coll@

2eturns a random element from

the collection(ran,nt [1 $ %]) => $

butlast2eturns the se%uence without the

last element.(butlast [1 $ %]) => (1 $)

take >n se%@2eturns a se%uence with the n first

elements of se%. (tae $ [1 $ %]) => (1 $)

take#last >n

se%@

2eturns a se%uence with the n last

elements of se%.(taelast $ [1 $ %]) => ($ %)

take#nth >n

coll@

2eturns a laFy se% of every nth

item in coll(taent $ [1 $ %]) => (1 %)

take#while

>f se%@

2eturns a se%uence with the

elements from start until f returns

false.

(taeile C(- B 6) '(1 * 10)) => (1*) (taeile C(> B 6) '(1 * 10)) =>()

drop >n s@

drop#last >n

s@drop#while

!s take, but removes the specified

items and returns the rest.

(,ro $ [1 $ %]) => (%) (,rolast $[1 $ %]) => (1)
http://clojure.org/lazyhttp://clojure.org/lazyhttp://clojure.org/lazyhttp://clojure.org/lazy


23/66

>f s@

keep >f s@2eturns a se% of the non#nil results

of (f item).

(ee first [[:a 1] [:b $]]) =>(:a :b)

keep#

inde3ed

!s keep, but passes the inde3 to f

along with the item.

(eein,exe, (fn [i "] i) [10 11])=> (0 1)

Use + modify

cons >elm

se%@

2eturns se% with elm added at the

front.(cons 1 '($ %)) => (1 $ %)

conj >se% ?

elms@

2eturns se% with one or more

elms added at the front.(con '(:a) :b :c) => (:c :b :a)

concat >s'

s@

2eturns se% from appending s to

the end of s'(concat [:a :b] [1 $]) => (:a :b 1 $)

distinct

>coll@

2eturns a se% of distinct (non#

e%ual) elements of coll.(,istinct [1 $ 1]) => (1 $)

group#by >f

coll@

2eturns a map of collection

elements keyed by the return

value of f.

(/roub+ C(- B 10) [1 $ $0 $1] =>{true [1 $] false [$0 $1]}

partition >n

coll@

partition >n

step coll@

partition >n

step pad

coll@

2eturns a laFy se% of lists of n

elements each, at offsets step

(default n) apart.

If the last list have less than n

elements it is skipped.

pad is an optional collection used

to fill up the last partition if there

are not enough elements to get

length n.

(artition $ [1 $ %]) => ((1 $))(artition $ 1 [1 $ %]) => ((1 $) ($%)) (artition $ 1 (reeat 0) [1 $%]) => ((1 $) ($ %) (% 0))

partition#all

>n coll@

!s partition, but includes the last

list even if it has less than n

elements.

(artitionall $ [1 $ %]) => ((1 $)(%))

partition#by

>f coll@

!s partition, but splits coll each

time f returns a new value.

(artitionb+ e"en? [1 $ %]) => ((1)($) (%)) (artitionb+ (artial - 10)[1 $ 11 1]) => ((1 $) (11) (1))

split#at >n

coll@

2eturns vector of >(take n coll)

(drop n coll)@(slitat $ [1 $ %]) => ((1 $) (%))

split#with>pred coll@ 2eturns vector of >(take#whilepred coll) (drop#while pred coll)@(slitit C(-= B $) [1 $ %]) => ((1$) (%))

filter >pred

coll@

remove

>pred coll@

7ilter returns a se%uence of the

items in coll where pred returns

true, remove the items where

pred returns false.

(filter e"en? [1 $ %]) => ($) (re&o"ee"en? [1 $ %]) => (1 %)

replace >map

coll@

2eturns a se% or vector where

collection elements e%ual to a

map key are replaced with the

map value.

(relace {:a 1 :b $} [:a :b %]) => [1$ %]

shuffle >coll@

2eturns a random permutation of

coll. (suffle [1 $ %]) => [% 1 $]

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Use + iterate

for >>? se%#

e3prs@ ?

body@

akes one or more pairs of bindings

and se%uences, each with Fero or more

modifiers, and iterates over all

elements in all se%uences, rightmostfastest.

2eturns a laFy se% of evaluating body

for each combination.

6odifiers are

let >binding e3pr ...@ # new

local vars

while test # stop the loop when

test turns false

when test # evaluate body only

when test is true

(for [x [:a :b]] x) => (:a :b)(for [x [1 $] + [:a :b] ] [x +]) => ([1 :a] [1 :b] [$ :a][$ :b]) (for [x (ran/e 10):en (e"en? x) + (ran/e x):en (e"en? (# x +)) :ile (-(# x +) 10) ] (# x +) ) => ($ *7 7 ; ;)

dose% >>?

se%#e3prs@

? body@

!s forbut does not collect results and

returns nil.

"rimarily used for side effects.

akes the same modifiers as for#

let, while and when

(,oseq [i [1 $ %]] (rint i ))=> 1 $ % (,oseq [i [1 $ %] :en

(@ero? (&o, i $)) ] (rint i ))=> $

map >f coll

? colls@

2eturns a laFy se% of the return value

of calling f on each element in coll.

If there are several colls, f must accept

the same number of args as there are

colls, and f is called on the first item of

each followed by the second etc., until

one of the colls is empty.

(&a inc [1 $ %]) => ($ % *) (&aC("ector B1 B$) [1 $ %] [* 6]) =>([1 *] [$ 6])

map#

inde3ed >fcoll ? colls@

!s map, but f gets the current inde3 as

the first argument.

(&a (fn [i "] [i "]) [:a :b]) =>([0 :a] [1 :b])

mapcat >f

coll ? colls@

!s map, but calls concat on the result,

so f should return a coll.

(&acat C(list B1 B$) [1 $] [*6]) => (1 * $ 6)

reduce >f

coll@

reduce >f

init coll@

2educes a series of items to a single

result.

f takes two args, the current item and

an accumulator with the result so far. f

is called on each item in coll and the

return value is passed on to the ne3t

call as the new value of the

accumulator.

If init is given, it is the value of the

(re,uce # [1 $ %]) => 7 sa&eusin/ inline function (re,uceC(# B1 B$) [1 $ %] => 7 (re,uceC(con B1 (inc B$)) [] [1 $ %])=> [$ % *] sa&e usin/ fullfunction (re,uce (fn [acc x](con acc (inc x))) [] [1 $ %])=> [1 $ %]

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accumulator at the first call. If not, the

accumulator is initialiFed with the

result of calling f on the first two items

in coll.

reductions >f

coll@reductions >f

init coll@

!s reduce, but returns a laFy se% of theintermediate values.

(re,uctions # [1 $ %]) => (% 7)(re,uctions # 0 [1 $ %]) => (0 1% 7)

ma3#key >f

? items@

!s ma3 for numbers, but returns the

item with the ma3 return value of f.

(&axe+ last [:x 1] [:+ $]) =>[:+ $]

min#key >f

? items@

!s ma3#key, but returns the item where

f returns the smallest number.

(&ine+ last [:x 1] [:+ $]) =>[:x 1]

doall >se%@

doall >n se%@

7orces evaluation of a laFy se%uence,

or the first n items.

2eturns the se%uence.

(,ef & (&a (fn [x] (rint x )x) [1 $ %] )) => no rintK &a is la@+ (,oall &) => 1 $ %=> (1 $ %)

dorun >se%@

dorun >n

se%@

!s doall, but returns nil.

9sed for side effects.

(let [res (&a (fn [x] (rint x) x) (ran/e %)) ]) => nil norintin/ la@+ e"al (let [res(&a (fn [x] (rint x ) x)(ran/e %)) ] (,orun res)) => 0 1$ rint

Transient

he standard collection type is called +persistent+ and is immutable, so +mutating+ operations

# add, remove etc. # returns a new collection.

!n e3perimental alpha feature is +transient+ collections, which are mutable for performance

reasons but not visible outside a single thread, thus giving both performance and thread

safety.

he usage scenario is one thread doing multiple modifications on a transient version, and

converting it back to a persistent version to share the data with other threads.

he ..W versions of conj, pop etc. are meant to be used by capturing the return value in the

same way as for immutable collections. It may work without doing so, but this is not

guaranteed.

Create

transient

>coll@

Converts to transient collection

of the same type.

(,ef t (transient [1 $ %])) =>C-AransientTector ...>

persistentW

>coll@

Converts transient arg back to a

persistent collection.

he transient collection cannot be

used afterwards.

(ersistentQ t) => [1 $ %] (conQ t*) => Excetion

Use

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conjW >t ?

items@

*estructively adds one or

more items to a transient

vector, list, se%uence or set.

(,ef t" (transient [1 $])) (ersistentQ(conQ t" % *)) => [1 $ % *]

popW >t@*estructive pop from

transient vector or list.

(ersistentQ (oQ (transient [1 $]))) =>[1]

assocW >m

? kvs@

*estructively adds one ormore key;value mappings to

a transient map or vector.

If vector, the keys are

integer inde3es B vector

length.

(,ef t" (transient [1 $])) (ersistentQ(assocQ t" 0 6)) => [6 $] (,ef t&(transient {:a 1 :b $})) (ersistentQ(assocQ t& :c %)) => {:a 1 :b $ :c %}

dissocW >t

? keys@

*estructively deletes one or

more key;value pair from a

transient map.

(ersistentQ (,issocQ (transient {:a 1 :b $:c %}) :a :b)) => {:c %}

disjW >t ?

vals@

*estructively deletes one or

more values from a transientset.

(ersistentQ (,isQ (transient C{:a :b})

:a)) => C{:b}

,unctions

7unctions are first#class values, and can be stored in variables or hash tables, passed as

parameters etc. just like any other value.

Create

fn Create an anonymous function. (fn [a b] (# a b))

S(..)

5ightweight synta3 for inline

anonymous function. 6eant for one#

liners, some limitations relative to

fn8ne arg is accessed as X,

multiple args as X', X etc.

C(# B1 B$)

defn >name doc#

string< metaparamsP@ ?

body@

Creates a function by given name,

with optional docstring and

metadata. 0ody is the function body.

here is also a version that allowsfor multiple bodies with different

number of arguments.

(,efn x [+] (# 1 +)) (,efn x+&+ function ([] (x+ 0)) ([i](rintln i)))

defn#

!s defn, but creates a private

function, not callable from other

namespaces.

definline

! cross between defn and defmacro

# creates a function but tries to inline

the body when the function is called.

:3perimental

identity! standard function that returns itsargument.

(i,entit+ 1) => 1 (i,entit+abc) => abc

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constantly >val@2eturns a function that always

returns the same value.((constantl+ *$)) => *$

memfn >name ?

args@

$ava method wrapper. 2eturns an fn

that accepts an object and optional

method args, and calls the namedmethod on the object with the args.

(,ef &l (&e&fn len/t)) Strin/.len/t (&l abc) => % Rile.len/t (&l (a"a.io.Rile.3etc3ass,)) => %775 (,ef &i(&e&fn in,exGf s)) Strin/.in,exGf (&i abc a) =>0

comp >f ? fs@

Compose. akes two or more

functions, returns a function that

calls the rightmost function with the

input args, the ne3t function (right to

left) with the output of the first

function etc., returning the result of

the last (leftmost) function.

((co& not e&t+?) []) => false

complement >f@

2eturns a function that returns the

boolean opposite of f.

!s (not (f ...))

((co&le&ent nil?) nil) => false

partial >f ?

args@

akes a function f accepting n args

and less than n default arguments.

2eturns a function that accepts the

remaining one or more args and

passes the defaults plus the new args

on to f.

!rgs to f are filled in from the left,

so the args accepted by the partial

function (the return value frompartial) are the last ones.

(,ef {:a 1}) (,ef /et(artial /et )) (/et :a) => 1

ju3t >? fs@

$u3taposition. akes a se%uence of

fns, returns a function that calls all

the fns on the input and returns a

vector of the results.

!lpha status.

((uxt inc ,ec) $) => [% 1]

memoiFe >f@

2eturns a cached version of the

argument function. Ahen called

with arguments it has received

before, returns the precomputed

value.

(,ef (&e&oi@e #))

Call

(...)

*irect normal fn call. he first

element in the list is e3pected to be

a function, the rest is arguments.

(# 1 $) => %

#D

Chain calls so output from the

leftmost fn is first arg to second fn

etc. he chain reads left to right or

top#down instead of the normalbottom#out.

(> (S+ste&3/etFroerties) (/eta"a."ersion)) => 1.7.0 sa&e as(/et (S+ste&3/etFroerties)

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#DD

!s #D, but returns are inserted as

last arg to ne3t fn rather than first

arg.

(>> (ran/e 6) (filter e"en?) (&ainc)) => (% 6) sa&e as (&a inc(filter e"en? (ran/e 6)))

apply >f

arglist@Call f with arguments in arglist.

(# 1 $ %) => 7 (# [1 $ %]) => Error(al+ # [1 $ %]) => 7

Test

fn< rue if arg is function(fn? inc) =>true (fn? :x) =>false

ifn(cloure.core3let [NXX$$* $ re$$6 %] (cloure.core3rint 1NXX$$* re$$6))

If evaluated with eval, this will print 1 $ %

?formImplicit argument, holds the entire macro.

AGMG

?envImplicit argument, holds a map of local bindings.

AGMG

/ava data types

Classes in java.lang are available by their short names. 8ther classes are available by their

fully %ualified name, i.e. java.util.Iterator. Importcan be done to get shorter names.

Clojure data types, values and variables are immutable (with a few e3ceptions), but $ava

values are fully mutable to the e3tent of their $ava implementation. Clojure provides a layer

of integration to call $ava from ClojureV but once there it is all $ava and $avas rules.

/ava objects

Create

(Class1ame.

argP)

(new

Creates a new object of

class Class1ame,

matching arguments to

(Gbect.) => C-a"a.lan/.GbectW$b7c0>(a"a.at.Foint. 1 $) =>

C-a"a.at.Foint[x=1K+=$]>

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Class1ame

argP)

constructor.

he +trailing dot+ and

+new+ notations are

e%uivalent.

Use

Class1ame;&!ICQ7I:5*!ccess a static

field.nte/er3SE => %$

(Class1ame;&!ICQ6:H8*

argP)

Call a static

method.

(S+ste&3/etFroert+a"a."ersion) => 1.7.0

(.method obj argP)Call an instance

method.

(.as!o,e (Gbect.)) =>1$*0$6$

doto >obj ? calls@

6ake multiple

method calls to the

same object, returnobject.

(,oto (a"a.util.

C-

(.. obj callO)

$ava call chaining.

he first call # a

method name and

any args # is applied

to the first object,

the ne3t call applied

to the return value

from the first etc.

&ame as #D e3cept

that the dot is addedso it works with

$ava calls.

(.. (S+ste&3/etFroerties) (/etos.na&e) (slit ))) =>[4acK GSK 8] sa&e as(.slit (./et(S+ste&3/etFroerties)os.na&e)) )

(setW (. obj field1ame) val)

(setW (. Class1ame field1ame)

val)

&et $ava field

values on object

(instance fields) or

class (static fields).

7ields must be

public and writable.

(,ef (a"a.at.Foint. $ $))=> C-Foint [x=$K+=$]> (setQ (. x) 10) => 10 => C-Foint[x=10K+=$]>

/ava arrays

Creating and accessing arrays can be done through $ava (via java.lang.reflect.!rray), but

Clojure provides some convenience functions.

Create

make#array

>type len@

Create $ava array of specified type and

length. ype is a $ava class. ypes of

primitive values are a field in their object

wrapper, e3. &hort;N":.

(&aearra+ Gbect $) => [nilKnil] Gbect[] (&aearra+nte/er3A9FE %) => [0K 0K 0] int[]

object# !s make#array, but takes only one arg, the (obectarra+ $) => [nilK nil] Gbect[]

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array >len@

boolean#

array

byte#array

char#array

short#arrayint#array

long#array

float#array

double#

array

length.

aclone >arr@ Creates a copy of an array.(aclone (toarra+ [1 $])) =>[1K $]

to#array

>coll@

Creates object array from a Clojure coll or

se%.

(toarra+ [1 $ %]) => [1K $K%] Gbect[]

to#array#d

>coll@ Creates a d array from nested Clojure coll.

(toarra+$, [[1 $] [% *]]) =>

[[1K $]K [%K *]] Gbect[][]

into#array

>se%@

into#array

>type se%@

Creates array from a Clojure se%. !rray will

be same type as the se% elements (which

must all be the same type) or of the

provided type. ype is a $ava class.

(intoarra+ [1 $]) => [1K $] nte/er[] (intoarra+nte/er3A9FE [1 $] ) => [1K $] int[]

Use

aget >arr i@

/et values from array at inde3. Aorks

on arrays of all types, including arrays

of primitives.

(,ef arr (toarra+ [1 $ %]))(a/et arr 1) => $

aset >arr i v@ &ets array value at inde3 i.(,ef arr (toarra+ [1 $ %]))(aset arr 0 ) => arr => [ $%]

aset#boolean

>arr i v@

aset#char

#byte

#int

#long

#short

#float#double

&et value in array of $ava primitives.

alength >a@ 5ength of array (alen/t arr) => %

amap >a i3 ret

e3pr@

6aps e3pression over array.

a is the array to map over

i3 is name of var holding current

inde3

ret is name of var holding return

value, initialiFed to a clone of a

e3pr is evaluated at each step

and return value placed in ret.

he original array is unchanged.

(,ef arr (toarra+ [1 $ %]))(a&a arr i ret (inc (a/et reti))) => [$ % *]

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areduce >a i3

ret init e3pr@

2educes e3pression over array.

a is the array

i3 is var holding the current

inde3

ret is var holding the reduced

value so far init is initial value

2et is set to init, e3pr is called for each

element and ret is updated to the return

value from e3pr.

2et is returned at the end.

(,ef arr (toarra+ [1 $ %]))(are,uce arr i ret 0 (# ret(a/et arr i))) => 7

Cast

booleans

bytes

chars

shorts

ints

longs

floats

doubles

*eclares value to be an array of a primitive type. *oes not convert.

/ava primitives

clojure.org $ava Interop under +&upport for $ava "rimitives+ is the current official

documentation.

Clojure wiki +:nhanced primitive support+ describes work in progress for '..

Type !ints

ype hints are changing in '.. he biggest change is that primitive type hints for long and

double may be allowed in certain circumstances, but the details are not yet finaliFed.

clojure.org $ava Interop under +ype hints+ is the current official documentation

Clojure wiki +:nhanced primitive support+ describes work in progress for '..

ype hints may matter for optimiFing inner loops. Clojure tries to derive types automatically

and falls back on reflection when it doesnt know which class to call. 2eflection is useful for

generality, but tend to be an order of magnitude slower than direct calls.

&etting the compiler flag Pwarn#on#reflectionP to true will print a warning when a method

call cannot be resolved.

\... ! type hint when prefi3ing a var no t+e int (,efn a [s] (.len/t s)) t+e int (,efn b [YStrin/ s] (.len/t

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name.

ype hints can occur almost

everywhere a var is declared or

referenced.

4alid type hints are $ava class

names or doubles, ints, objects etc.for $ava arrays, see Casts under

s)) t+e int (,efn c [s] (.len/tYStrin/ s))

/ava pro$ies

$ava subclassing and interface implementations.

here are two ways to create a pro3y # the all#in#one function rox+or the three#step /etrox+class3constructrox+3initrox+.

Create

pro3y >>cls< ?

interfaces@ >?

args@ ? fns@

Creates a pro3y, a single instance of an anonymous class, which subclasses cls

(optional, defaults to 8bject) and implements interfaces.

args # a vector of args to the superclass constructor, empty if none.

fns # a list of function implementations on the form(na&e [ara&sD] bo,+) or(na&e ([ar/] bo,+) ([a1 a$] bo,+)...)

he latter form is for methods with multiple signatures.

this is bound in the body of the functions.

(,efn it [coll] a"a iterator o"er seq3coll. (let [c (ato&(seq coll)) ] nee, to ee state (rox+ [a"a.util.terator][] (as2ext [] (boolean Wc)) (next [] (ennot Wc (tro(a"a.util.2oSucEle&entExcetion.))) (let [ret (first Wc)](saQ c next) ret )) (re&o"e [] (tro(Znsuorte,GerationExcetion.))))))

get#pro3y#

class >c< ?

interfaces@

akes an optional class c (defaults to 8bject) and one or more interfaces, and

returns a pro3y class that e3tends c and implements the interfaces with noop

methods.

construct#

pro3y >c ?

args@

akes a pro3y class c and args for the c superclass constructor, and returns a

pro3y instance.

init#pro3y

>pr3 fn#map@

InitialiFes pro3y instance pr3 with name#to#function fn#map. 7ns must take an

e3plicit first arg corresponding to +this+.

)isc

pro3y#

mappings

>pr3@

2eturns a map of method#name to function for pro3y.

(rox+&ain/s (it [1 $ %])) {re&o"e C-user...fnXX$$;7Wb6a11e>K next C-user...fnXX$$;W67a7eba>Kas2ext C-user...fnXX$$$W%e%e%c;%>}

pro3y#super

>mname args@ Calls superclass method with name and args in the body of a pro3y method.

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update#pro3y

>pr3 fn#map@!s init#pro3y, but updates an e3isting pro3y instance with new methods.

Clojure in /ava

7or making Clojure code callable from $ava, use the :/enclassand :/eninterface

options to nsand pre#compile stub classes using co&ile

&ee

clojure.org Compilation and Class /eneration

gen#class !"I doc

gen#interface !"I doc

compile !"I doc

*efrecord and deftype also give $ava#callable classes.

'perations

,lo" control

Constructs to control the e3ecution flow of the program # whether, when and how often

which e3pressions are evaluated, plus the special cases of assertions and e3ceptions.

he separation of +flow+ (if, for, while...) from other operations (function calls) is less clear

cut in Clojure than in other languages, as many se%uence operations can be considered flowcontrol # e3. map, reduce, dose%, dotimes, some, every< etc. are all variations over a C#style

for.

hose few I consider to be more of a +control+ nature rather than an +operations on data+

nature are repeated below. &ee se%uencefor the rest.

5aFiness is a form of flow control, and many;most se%uences are laFy. I have included a few

ops that deal specifically with creating and cancelling laFiness, see se%uence for the rest.

Normal

if >test then

else@

:valuates the test e3pression. Ifthe test evaluates to a logical

true value, evalues the then

e3pression, otherwise the else

e3pression.

(if (- 1 $) (rintln less) (rintlnnot less)) => less

if#not >test

then else@

!s if, but evalues the test with a

not.

(ifnot (- 1 $) (rintln not less)(rintln less)) => less

if#let >>bind

e3pr@ then

else@

If and let in one If the second

e3pression in the test form

evaluates to logical true, assigns

the variables as with let ande3ecutes the then branch.

(iflet [a (# 1 1)] (rintln a)(rintln :false)) => $ (iflet [[a b][1 1] ] (rintln a) (rintln :false))=> 1 (iflet [[a b] nil] (rintln a)(rintln :false)) => :false

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when >test ?

body@

!s if, but without an else

branch and with an implicit do.

(en (- 1 $) (rint 1 ) (rintln$)) => 1 $

when#not

>test ?

body@

!s when, but evaluates test in a

not.

(ennot (- 1 $) (rint 1 )(rintln $)) => nil

when#let !s if#let for when (enlet [[a b] [1 $]] (rint a )(rintln b)) => 1 $

when#first

&ets the binding to first element

in the se%uence, and evaluates

the body unless the se% is

empty.

(enfirst [a [1 $]] (rintln a)) =>1 (enfirst [a ()] (rintln a)) =>nil

cond

6ultiform if # takes any number

of conditions and evaluates the

first branch where the condition

is logical true.

2eturns nil if no match.

(con, (- $ 1) :lt (= $ 1) :eq (> $1) :/t) => :/t

condp >pred

v ? clauses@

&imple cond 9ses the same test

function for all values, and

returns the first branch where

(pred test#e3pr v) returns true.

he predicate can be any fn that

accepts two args.

! clause comes in two forms

test#e3pr result#e3pr

If test e3pr matches,

evaluates and returns

result#e3pr test#e3pr DD result#fn

If test#e3pr matches,

calls result#fn, a '#

argument function, with

the result of the test.

he two forms can be mi3ed in

the same condp.

he last entry may be a single

default, which is evaluated if

there is no other match.hrows e3ception if no match

and no default e3pression.

! more comple3 e3ample

(con, so&e [1 $ *] C{$*} :>> (artial D 10) C{16} :>> i,entit+) => $0(con, so&e [1 %] C{$*} :>> (artial D 10) C{16} :>> i,entit+) => 1

his e3pands to

(con, = (# 1 1) (# 0 0) :@ero (# 1 0):one $ :to :oter) => :to (con, >=100 10 :s&all 100 :&e,iu& 1000:lar/e :u/e) => :&e,iu& (con, /et :aC{:b :c} foun, b C{:a :e} foun, a)=> foun, a (con, = 1 0 0 1 :>> inc$ :>> ,ec ) => $

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(so&e C{$ *} [1 $ *])

which calls(C{$ *} n)

on each vector element in turn.

his is a set lookup, returning nif n is in the set.

so&ereturns the first element in

the vector found in the set, so

is found before G.

he matching n is then passed

to the result#fn.

&ince test e3pressions are

evaluated in order, the match on

in ST GU is found before thematch on ' in ST' LU

case >v (test#

v e3pr)O@

&imilar to condp, but only for

e%uality and compile#time

literal constants in the test

values.

5ookup is a constant time

dispatch, the test e3pressions

are not evaluated.

(case (# 1 1) 0 :@ero 1 :one :oter)=> :oter

do >? body@

:valuates its arguments in

order, returns the last value.

9sed to put multiple

e3pressions in forms that only

accept single e3pressions, like if

or cond clauses.

(if (- 1 $) (,o (rint less) 1)) =>less => 1

eval >form@

:valuates the form and returns

the result.

he form is a Clojure data

structure as returned by the

reader, not te3t.

'(# 1 $) => (# 1 $) (e"al '(# 1 $)) =>% (e"al (# 1 $)) => (# 1 $) (e"al(rea,strin/ (# 1 $) )) => %

loop

>bindings@recur >?

args@

2ecursive behavior without

using stack space.

If recur is used with loop,

repeats the loop.

If used without loop, loops from

the start of the function. !rgs

must be those accepted by the

fn.

In a function with multiple

arities (multipleimplementations taking a

(loo [i 0] (if (>= i 10) i (recur(inc i)))) => 10 (,efn incuntil [i n](if (>= i n) i (recur (inc i) n)))(incuntil 0 10) => 10 (,efn incuntil([i] (incuntil 10)) ([i n] (recur(inc i)))) => !o&ilerExcetion

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different number of arguments),

recur can only loop from the

start of the same arity.

trampoline

>f ? args@

!s recur for mutually recursive

functions # a way to get mutualrecursion without using stack

space.

Calls f with supplied args. If f

returns an fn, keep calling the

fns (with no args) until the

return value is no longer an fn.

he final value is returned.

(,eclare on/) (,efn in/ [n] (en(os? n) (rintln in/ n) C(on/(,ec n)))) (,efn on/ [n] (en (os?n) (rintln on/ n) C(in/ (,ecn)))) (tra&oline in/ 6) => in/ 6on/ * in/ % on/ $ in/ 1 nil

while >test

? body@

:3ecutes body while test is true.

Nou will need some sort of side

effect to cause the test to change

value.

(let [a (ato& $)] (ile (> Wa 0)(rint Wa ) (saQ a ,ec))) => $ 1

0$ceptional

7low control outside normal program flow.

assert >e3pr@

2eturns nil if e3pr evaluates to

logical true, throws ane3ception otherwise.

9sed for testing and for

checking function pre# and

post conditions.

(assert (= 1 1)) => nil (assert :a) =>nil (assert (= 1 $)) => Excetion:? body@

catch >e#class

e#var ?

body@

finally >?

body@

throw

>e3ception@

Create and deal with

e3ceptions.

throw # throws an

e3ception based on a

$ava :3ception class

akes one arg, an

e3ception object.

try # starts a block in an

implicit doV the block

must end with catch

and;or finally.

catch # catches an

e3ception thrown

between the try and the

catch.

here may be multiple

catch statements basedon different subclasses

(tr+ (tro (Lunti&eExcetion. oos))(catc Excetion e (rintln cau/t(./et4essa/e e)) retro (tro e))(finall+ (rintln cleanu))) =>startin/ cau/t oos cleanuC-Lunti&eExcetion: oos>

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of java.lang.hrowable

o e#class the $ava

:3ception class

the catch will

work for

o var variablename to use for

the e3ception

inside the catch

body.

finally # e3ecutes its

body whether or not an

e3ception was thrown.

8ptional. 1ormally

used to ensure that

files, connections etc.

are closed after use

even in the face of

e3ceptions.

Can be used alone

(with try) or together

with one or more catch

e3pressions.

1elay

delay >?

body@

*elays the evaluation of body until the value

is re%uested by deref;[ or force

create ,ela+ (,ef x (,ela+(rintln o,+))) reference it Wx => o,+ =>nil

[...

deref

*ereference the value of a delay. (8r atom,

future etc., see Concurrency). 0locks until

the value is available the first time it

accessed.

force

>delay@

7orce the evaluation of a delay object.

!lternative to deref;[. 2eturns immediately.

delayd@

rue if arg is a delay.

,unction based

&ee &e%uence

repeatedly 2f3# laFy se%uence which calls no#arg function f repeatedly

iterate 2f init3# laFy se%uence of init, (f init), (f (f init)) etc.

Sequence based

&ee &e%uence

dotimes# e3ecutes body n times, returns nil

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doseq# e3ecutes body for each element in se%uence(s), returns nil

for# e3ecutes body for each element in se%uence(s), returns new se%uence

La*iness

&ee &e%uence

la*y+seq# create laFy se%uence

la*y+cat# create laFy se%uence

doall# force evaluation of laFy se%uence, return result

dorun# force evaluation of laFy se%uence, do not return result

Type inspection

Clojure types

type >arg@2eturns the type meta#dataof arg, or its

class if none.

(t+e 1) =>a"a.lan/.nte/er

e3tends< >p

type@

rue if type e3tends protocol p.

($ava analogue *oes type implement

interface pp

val@

rue if val satisfies protocol p.

($ava analogue val instanceof parg@ 2eturns the $ava class of arg.(class 1) => a"a.lan/.nte/er (classnte/er) => a"a.lan/.!lass

bases >cls@

2eturns a se% of immediate

superclasses and direct

interfaces of cls.

(bases nte/er) => (a"a.lan/.2u&bera"a.lan/.!o&arable)

supers >cls@2eturns a set of all superclasses

and interfaces of cls.

(suers nte/er) => C{a"a.lan/.2u&bera"a.lan/.Gbect a"a.io.Seriali@ablea"a.lan/.!o&arable }

class< >arg@ rue if arg is a class. (class? nte/er) => true

instancecls obj@

rue if obj is an instance of cls. (instance? 2u&ber 1) => true

isa< >sub

super@

rue if sub#cls inherits from

super#cls.

*iffers from instance< in

working on classes rather than

instances.

isa< also works foruser#

defined hierarchies

(isa? nte/er 2u&ber) => true (isa? 12u&ber) => false

cast >cls

obj@

4erifies that obj is an instance

of class c.

hrows ClassCast:3ception or

returns obj.

(cast 2u&ber 1) => 1 (cast 2u&ber a) =>!lass!astExcetion

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Concurrency

8ne of the goals of Clojure is to simplify programming with concurrency # dealing with locks

and threads is inherently hard.

7unctional programming with immutable data is in principle well suited to concurrency #

with no data sharing there are no concurrency issues.

6any programs still need data sharing, so Clojure has special constructs to simplify common

cases.

Concurrency constructs

atom6utable atomic variable # all reads and writes are atomic.

9sed for sharing a single value between threads, or in single#threaded programs to get

mutability.

ref6utable atomic variable, can only be updated inside a transaction.

9sed when there are several shared variables that must be updated simultaneously.o transaction9sed with refs. Inside a transaction refs can be read and updated.

If an e3ception occurs the transaction will be rolled back and the refs restored

to the values they had at the start of the transaction.

future&ingle asynchronous task.

! future is a function running asynchronously in a separate thread plus a variable used

to communicate return value back to the origin.

9sed when you want code to run in a background thread, for e3ample a download.

2eferencing a future will block until the value is available. he value is set only once,

and can be freely referenced without blocking afterwards.

agent6ultiple asynchronous tasks.

5ike a future, but lets you %ueue up multiple tasks that are e3ecuted one by one.9nlike futures, agents

o have a job ueue

$obs (functions) are added to the %ueue with send or send#off, and will

be run in order by the agent, one job at a time.

here is one job %ueue per agent.

o get multiple jobs running simultaneously, you need multiple agents.

o have internal state

here is one +current state+ variable per agent.

he state value can be as comple3 as you like.

he current state is passed to a job function when it starts and is set tothe return value of the job when it returns.

here is only one job running per agent at any time, so there are no

concurrency issues with the shared state.

o "o not bloc on rea"in)

!n agent variable can be read at any time without blocking

It will return the agent state at that moment in time.

his could be the initial value if no jobs have returned yet.

o use a threa" ool

here is one system#wide thread pool for all agents on the system.

o have error han"lin) mechanisms

!n e3ception in a job will by default stop the agent from continuing,leaving remaining jobs in the %ueue suspended.

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his can be controlled by an error mode flag (fail or continue).

8ne can also set error handlersV functions that are called when an error

happends.

o have mana)ement mechanisms

!n agent can be restarted or the whole agent thread pool can be shut

down. validator! function that validates a new value to be stored in an agent, ref or atom.

General

hese operations apply to most concurrency constructs.

[

deref

2eads and returns the current (most recently

commited) value of an atom, ref, future, agent or

delay.

8n futures and delays a deref will block until the

value is available.

2eturns immediately for the other types.

(,ef x (ato& 0)) =>C- Wx => 0

get#validator

>iref@

set#validatorW

>iref fn@

/ets or sets the validator function for a ref, agent or

atom.

he validator takes one arg, the new value, and

throws an e3ception if the value is invalid.

tom

&ee clojure.org atoms

Create

atom >init#val

? options@

Creates an atom, a mutable variable protected by

locks, with an initial value. he value can be simple

or comple3, eg. a map.

8ptions are optional, and can be (metadata#map)

and;or (a validator fn).

(,ef count (ato& 0))=> C- Wcount=> 0

Use

swapW >atom f@

9pdates value of atom.

f takes one arg, the current

value, and returns the new

value.

(saQ count inc) => 1

resetW >atom v@ &ets atom to new value v. (resetQ count 100) => 100 Wcount => 100

compare#and#setW

>a old#v new#v@

&ets atom a to new#v only

if current value is old#v.

2eturns true if set

happened, else false.

(co&arean,setQ count 100 0) => trueWcount => 0 (co&arean,setQ count 110) => false Wcount => 0

#ef

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&ee clojure.org refs

Create

ref >v ?

options@

Creates ref with initial value v and Fero or more

options.8ptions

meta # metadata map

validator # fn that gets passed all new values

to be stored in the ref, can return false or

throw e3ception if value is invalid.

min#history # min. number of historical

values to keep for rollback. *efault

ma3#history # ma3. number of histor

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