• |  | Racket Cheat Sheet

Racket Cheat Sheet
Essentials
Primitives
Data
Systems
Syntax (Beginner)
Syntax (Intermediate)
Syntactic Abstractions
Tools

7.2
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## Racket Cheat Sheet

Jay McCarthy

Essentials

Sites | main download docs git
Community | packages users@ dev@ irc slack twitter
Running | Put #lang racket "Hello, world!" in hello.rkt and run racket hello.rkt

Primitives

## Numbers

Literals | integer 1 rational 1/2 complex 1+2i floating 3.14 double 6.02e+23 hex #x29 octal #o32 binary #b010101
Arithmetic | + - * / quotient remainder modulo add1 sub1 max min round floor ceiling sqrt expt exp log sin ... atan
Compare | = < <= > >=
Bitwise | bitwise-ior bitwise-and bitwise-xor bitwise-not arithmetic-shift integer-length
Format | number->string string->number real->decimal-string
Test | number? complex? ... exact-nonnegative-integer? ... zero? positive? negative? even? odd? exact? inexact?
Misc | random
Match Pattern | (? number? n) 42

## Strings

Literals | "Racket" quoting "a \" approaches!" unicode "λx:(μα.α→α).xx"
Create | make-string string string-append build-string string-join
Observe | string-length string-ref substring string-split in-string
Modify | string-downcase string-upcase string-trim
Test | string? string=? string<=? string-ci<=?
Regexp | #rx"a|b" #rx"^c(a|d)+r$" regexp-quote regexp-match regexp-split regexp-replace regexp-replace*
Match Pattern | (? string? s) "Banana?"

## Bytes

Literals | #"rawbytes\0"
Create | make-bytes bytes
Numbers | integer->integer-bytes real->floating-point-bytes
Observe | bytes-length bytes-ref subbytes in-bytes
Modify | bytes-set! bytes-copy! bytes-fill!
Conversion | bytes->string/utf-8 string->bytes/utf-8
Test | bytes? bytes=?
Match Pattern | (? bytes? b) #"0xDEADBEEF"

## Other

Booleans | #t #f not equal?
Characters | #\a #\tab #\λ char? char->integer integer->char char<=? ... char-alphabetic? ...
Symbols | 'Racket symbol? eq? string->symbol gensym
Boxes | box? box unbox set-box! box-cas!
Procedures | procedure? apply compose compose1 keyword-apply procedure-rename procedure-arity curry arity-includes?
Void | void? void
Undefined | undefined

Data

## Lists

Create | empty list list* build-list for/list
Observe | empty? list? pair? length list-ref member count argmin argmax
Use | append reverse map andmap ormap foldr in-list
Modify | filter remove ... sort take drop split-at partition remove-duplicates shuffle
Match Pattern | (list a b c) (list* a b more) (list top more ...)

## Immutable Hash

Create | hash hasheq
Observe | hash? hash-ref hash-has-key? hash-count in-hash in-hash-keys in-hash-values
Modify | hash-set hash-update hash-remove

## Vector

Create | build-vector vector make-vector list->vector
Observe | vector? vector-length vector-ref in-vector
Modify | vector-set! vector-fill! vector-copy! vector-map!
Match Pattern | (vector x y z) (vector x y calabi–yau ...)

## Streams

Create | stream stream* empty-stream
Observe | stream-empty? stream-first stream-rest in-stream

## Mutable Hash

Create | make-hash make-hasheq
Observe | hash? hash-ref hash-has-key? hash-count in-hash in-hash-keys in-hash-values
Modify | hash-set! hash-ref! hash-update! hash-remove!

Systems

## Input/Output

Formatting | ~a ~v ~s ~e ~r pretty-format
Input | read read-bytes peek-byte
Output | write write-bytes display displayln pretty-print
Ports and Files | with-input-from-file with-output-to-file flush-output file-position make-pipe with-output-to-string with-input-from-string port->bytes port->lines ...

## Files

Paths | build-path bytes->path path->bytes path-replace-suffix ...
Files | file-exists? rename-file-or-directory copy-directory/files current-directory make-directory delete-directory/files directory-list filesystem-change-evt file->bytes file->lines make-temporary-file

## Miscellaneous

Time | current-seconds current-inexact-milliseconds date->string date-display-format
Command-Line Parsing | command-line
FFI | ffi-lib _uint32 ... _fun malloc free

## Networking

TCP | tcp-listen tcp-connect tcp-accept tcp-close
HTTP | http-conn http-conn-open! http-conn-send! http-conn-recv! http-conn-sendrecv! http-sendrecv
URLs | string->url url->string url-query
Email | smtp-send-message imap-connect ...
JSON | write-json read-json
XML | read-xml write-xml write-xexpr
Databases | postgresql-connect mysql-connect sqlite3-connect query-exec query-rows prepare start-transaction ...

## Security

Custodians | make-custodian custodian-shutdown-all current-custodian
Sandboxes | make-evaluator make-module-evaluator

## Concurrency

Threads | thread kill-thread thread-wait make-thread-group
Events | sync choice-evt wrap-evt handle-evt alarm-evt ...
Channels | make-channel channel-get channel-put
Semaphores | make-semaphore semaphore-post semaphore-wait
Async Channels | make-async-channel async-channel-get async-channel-put

## Parallelism

Futures | future touch processor-count make-fsemaphore ...
Places | dynamic-place place place-wait place-wait place-channel ...
Processes | subprocess system*

Syntax (Beginner)

## Basics

Modules | (module+ main body ...) (module+ test body ...) (require mod-path) (provide id)
S-expressions | quote '(a b c) quasiquote unquote `(1 2 ,(+ 1 2))
Procedure Applications | (fn arg1 arg2) keyword args (fn arg1 #:key arg2) (apply fn arg1 (list arg2))
Procedures | (lambda (x) x) (λ (x) x) (λ (x [opt 1]) (+ x opt)) (λ (x #:req key) (+ x key)) (λ (x #:opt [key 1]) (+ x key))
Binding | (let ([x 1] [y 2]) (+ x y)) (let* ([x 1] [x (+ x 1)]) x)
Conditionals | (if (zero? x) 0 (/ 1 x)) (cond [(even? x) 0] [(odd? x) 1] [else "impossible!"]) and or
Definitions | (define x 1) (define (f y) (+ x y))
Iteration | for for/list for*
Blocks | begin when unless
Require Sub-forms | prefix-in only-in except-in rename-in for-syntax for-label ...
Provide Sub-forms | all-defined-out all-from-out rename-out ... contract-out

## Structures

Definition | (struct dillo (weight color))
Create | (define danny (dillo 17.5 'purple))
Observe | (dillo? danny) (dillo-weight danny) (dillo-color danny)
Modify | (struct-copy dillo danny ([weight 18.0]))
Match Pattern | (dillo w c)

## Pattern Matching

Basics | (match value [pat body] ...)
Definitions | (match-define pat value)
Patterns | (quote datum) (list lvp ...) (list-no-order pat ...) (vector lvp ...) (struct-id pat ...) (regexp rx-expr pat) (or pat ...) (and pat ...) (? expr pat ...)

Syntax (Intermediate)

## Basics

Mutation | set!
Exceptions | error with-handlers raise exit
Promises | promise? delay force
Continuations | let/cc let/ec dynamic-wind call-with-continuation-prompt abort-current-continuation call-with-composable-continuation
Parameters | make-parameter parameterize
External Files Needed at Runtime | define-runtime-path
Continuation Marks | continuation-marks with-continuation-mark continuation-mark-set->list
Multiple Values | values let-values define-values call-with-values

## Contracts

Basics | any/c or/c and/c false/c integer-in vector/c listof list/c ...
Functions | -> ->* ->i
Application | contract-out recontract-out with-contract define/contract

## Iteration

Sequences | in-range in-naturals in-list in-vector in-port in-lines in-hash in-hash-keys in-hash-values in-directory in-cycle stop-before stop-after in-stream
Generators | generator yield in-generator

## Structures

Sub-structures | (struct 2d (x y)) (struct 3d 2d (z)) (2d-x (3d 1 2 3))
Mutation | (struct monster (type [hp #:mutable])) (define healie (monster 'slime 10)) (set-monster-hp! healie 0)
Transparency | (struct cash ($ ¢) #:transparent) (struct->vector (cash 5 95))
Printing | (struct nickname [n v] #:methods gen:custom-write [(define (write-proc nn p mode) (fprintf p (nickname-n nn)))]) (displayln (nickname "evens" (in-range 0 100 2)))
Serialization | (struct txn (who what where) #:prefab) (write (txn "Mustard" "Spatula" "Observatory"))

## Generics

Definition | define-generics
Instantiation | (struct even-set () #:methods gen:set [(define (set-member? st i) (even? i))])

## Classes

Definition | interface class*
Instantiation | make-object new instantiate
Methods | send send/apply send/keyword-apply send* send+
Fields | get-field set-field!
Mixins | mixin
Traits | trait trait-sum trait-exclude trait-rename ...
Contracts | class/c instanceof/c is-a?/c implementation?/c subclass?/c

Syntactic Abstractions

Definition | define-syntax define-simple-macro begin-for-syntax for-syntax
Templates | syntax syntax/loc with-syntax
Parsing ()-Syntax | syntax-parse define-syntax-class pattern
Syntax Objects | syntax-source syntax-line ... syntax->datum datum->syntax generate-temporaries format-id
Transformers | make-set!-transformer make-rename-transformer local-expand syntax-local-value syntax-local-name syntax-local-lift-expression ...
Syntax Parameters | define-syntax-parameter syntax-parameterize syntax-parameter-value
Parsing Raw Syntax | lexer parser cfg-parser

Tools

## Packages

Inspection | raco pkg show
Finding | pkgs.racket-lang.org
Installing | raco pkg install
Updating | raco pkg update
Removing | raco pkg remove

## Miscellaneous

Compiling | raco make program.rkt
Testing | raco test program.rkt a-directory
Building Executables | raco exe program.rkt
Extending DrRacket | drracket:language:simple-module-based-language->module-based-language-mixin
Slides | slide standard-fish code

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