Racket Cheatsheet

Sample program

#lang racket/base
(print "Hello, World!")

• #lang : to define the language you are using
• print : To display the output in the console
• ; : To comment a single line
• ;; : To mark important comments
• #; : To comment the following s-expression

Data types

Datatype	Description
Numbers	represents integers, float and complex numbers
Boolean	#t and #f are the two boolean literals
Strings	To represent sequence of characters, double quotes("") are used to represent strings

Variables

Both let and define can be used to define variables.

(let ([id value-expression] ...) body ...+)

(let proc-id ([id init-expression] ...) body ...+)

define id expression

Example

(let ([x 10]) x)

Lists

(list values)

Example

(list 1 2 3 4 5)

List Functions	Usage	Description
length	(length (list 1 2 3 4 5))	returns length of the list
list-ref	(list-ref (list "a" "b" "c") 0)	returns list item at an index
append	(append (list "a" "b") (list "c"))	to append two lists
reverse	(reverse (list "a" "b" "c"))	to reverse a list
member	(member "g" (list "a" "b" "c"))	checks if an element is present in a list

Conditional statements

1. If

(if cond-expr then-expr)

2. If-else

(if cond-expr then-expr else-expr)

Loops

1. For

(for (for-clause ...) body-or-break ... body)

where

for-clause = [id seq-expr] | [(id ...) seq-expr] | #:when guard-expr | #:unless guard-expr | break-clause

body-or-break= body | break-clause

Functions

(def fn functionName args body ...+)

Example

#lang racket/base
(define (square y) (* y y))
(square 5)

Procedures

(lambda (argument-id ...)
  body ...+)