Clojure 1.3-1.6 Cheat Sheet (v13)

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clojure.repl/ doc find-doc apropos source pst javadoc ( is namespace for later syms)



Literals Long: 7, hex 0xff, oct 017, base 2 2r1011, base 36 36rCRAZY BigInt: 7N Ratio: -22/7 Double: 2.78 -1.2e-5 BigDecimal: 4.2M
Arithmetic + - * / quot rem mod inc dec max min
Compare = == not= < > <= >= compare
Bitwise bit-{and, or, xor, not, flip, set, shift-right, shift-left, and-not, clear, test} (1.6) unsigned-bit-shift-right
Cast byte short int long float double bigdec bigint num rationalize biginteger
Test zero? pos? neg? even? odd? number? rational? integer? ratio? decimal? float?
Random rand rand-int
BigDecimal with-precision
Unchecked *unchecked-math* unchecked-{add, dec, divide, inc, multiply, negate, remainder, subtract}-int


Create str format See also IO/to string
Use count get subs compare (clojure.string/) join escape split split-lines replace replace-first reverse (1.5) re-quote-replacement (java.lang.String) .indexOf .lastIndexOf
Regex #"pattern" re-find re-seq re-matches re-pattern re-matcher re-groups (clojure.string/) replace replace-first (1.5) re-quote-replacement
Letters (clojure.string/) capitalize lower-case upper-case
Trim (clojure.string/) trim trim-newline triml trimr
Test char char? string? (clojure.string/) blank?


Characters char char-name-string char-escape-string
Keywords keyword keyword? find-keyword
Symbols symbol symbol? gensym



Generic ops count empty not-empty into conj (clojure.walk/) walk prewalk prewalk-demo prewalk-replace postwalk postwalk-demo postwalk-replace
Content tests distinct? empty? every? not-every? some not-any?
Capabilities sequential? associative? sorted? counted? reversible?
Type tests coll? list? vector? set? map? seq? (1.6) record?


Create '() list list*
Examine first nth peek .indexOf .lastIndexOf
'Change' cons conj rest pop


Create [] vector vec vector-of
Examine (my-vec idx)( nth my-vec idx) get peek .indexOf .lastIndexOf
'Change' assoc pop subvec replace conj rseq
Ops (1.4) mapv filterv reduce-kv


Create #{} set hash-set sorted-set sorted-set-by
Examine (my-set item)( get my-set item) contains?
'Change' conj disj
Rel algebra (clojure.set/) join select project union difference intersection
Get map (clojure.set/) index rename-keys rename map-invert
Test (clojure.set/) subset? superset?


Create {} hash-map array-map zipmap sorted-map sorted-map-by bean frequencies group-by
Examine (:key my-map)( get my-map :key) get-in contains? find keys vals
'Change' assoc assoc-in dissoc merge merge-with select-keys update-in
Entry key val
Sorted maps rseq subseq rsubseq

Transients (

Create transient persistent!
Change conj! pop! assoc! dissoc! disj! Note: always use return value for later changes, never original!


Compare = == identical? not= not compare
Test true? false? instance? nil? (1.6) some?


to/from ... spit slurp (to writer/from reader, Socket, string with file name, URI, etc.)
to *out* pr prn print printf println newline (clojure.pprint/) print-table
to writer (clojure.pprint/) pprint cl-format also: (binding [*out* writer] ...)
to string format with-out-str pr-str prn-str print-str println-str
from *in* read-line ( read
from reader line-seq ( read also: (binding [*in* reader] ...)
from string with-in-str ( read-string
Open with-open ( text: reader writer binary: input-stream output-stream
Binary (.write ostream byte-arr) (.read istream byte-arr) GitHub: gloss byte-spec
Misc flush (.close s) file-seq *in* *out* *err* ( file copy delete-file resource as-file as-url as-relative-path GitHub: fs
Data readers (1.4) *data-readers* default-data-readers (1.5) *default-data-reader-fn*







Abstractions (Clojure type selection flowchart)

Protocols (

Define ( defprotocol Slicey (slice [at]))
Extend ( extend-type String Slicey (slice [at] ...))
Extend null ( extend-type nil Slicey (slice [_] nil))
Reify ( reify Slicey (slice [at] ...))

Records (

Define ( defrecord Pair [h t])
Access (:h (Pair. 1 2))1
Create Pair. ->Pair map->Pair

Types (

Define ( deftype Pair [h t])
Access (.h (Pair. 1 2))1
Create Pair. ->Pair
With methods ( deftype Pair [h t]
  (toString [this] (str "<" h "," t ">")))

Multimethods (

Define ( defmulti my-mm dispatch-fn)
Method define ( defmethod my-mm :dispatch-value [args] ...)
Dispatch get-method methods
Remove remove-method remove-all-methods
Prefer prefer-method prefers
Relation derive isa? parents ancestors descendants make-hierarchy

Reader Macros

' Quote: 'form(quote form)
\ Character literal
; Single line comment
^ Metadata (see Metadata section)
@ Deref: @form(deref form)
` Syntax-quote
~ Unquote
~@ Unquote-splicing
#"p" Regex Pattern p
#' Var quote: #'x(var x)
#() #(...)(fn [args] (...))
#_ Ignore next form

Metadata (

General ^{:key1 val1 :key2 val2 ...}
Abbrevs ^Type^{:tag Type}
^:key^{:key true}
Common ^:dynamic ^:private ^:doc ^:const
Examples (defn ^:private ^String my-fn ...)
(def ^:dynamic *dyn-var* val)
On Vars meta with-meta vary-meta alter-meta! reset-meta! doc find-doc test


Current *ns*
Create/Switch (tutorial) ns in-ns create-ns
Add alias def import intern refer
Find all-ns find-ns
Examine ns-{name, aliases, map, interns, publics, refers, imports}
From symbol resolve ns-resolve namespace
Remove ns-unalias ns-unmap remove-ns


Load libs (tutorial) require use import refer
List loaded loaded-libs
Load misc load load-file load-reader load-string


Atoms atom swap! reset! compare-and-set!
Futures future future-{call, done?, cancel, cancelled?} future?
Threads bound-fn bound-fn* {get, push, pop}-thread-bindings thread-bound?
Misc locking pcalls pvalues pmap seque promise deliver

Refs and Transactions (

Create ref
Examine deref @ (@form(deref form))
Transaction sync dosync io!
In transaction ensure ref-set alter commute
Validators set-validator! get-validator
History ref-history-count ref-{min, max}-history

Agents and Asynchronous Actions (

Create agent
Examine agent-error
Change state send send-off restart-agent (1.5) send-via set-agent-send-executor! set-agent-send-off-executor!
Block waiting await await-for
Ref validators set-validator! get-validator
Watchers add-watch remove-watch
Thread handling shutdown-agents
Error error-handler set-error-handler! error-mode set-error-mode!
Misc *agent* release-pending-sends

Many thanks to:
  • Steve Tayon for creating the cheat sheet
  • Andy Fingerhut for tireless automation and tending
Logo & site design by Tom Hickey.