Racket Cheat Sheet
Fundamental Racket syntax covering definitions, higher-order functions, list operations, and pattern matching with match.
2 PagesIntermediateApr 10, 2026
Basics
Definitions and printing.
racket
#lang racket;; Definitions and printing(define name "World")(displayln (string-append "Hello, " name "!"))(define (square x) (* x x))(displayln (square 5))
Functions
Lambdas, local bindings, and higher-order functions.
racket
;; Anonymous functions (lambda)(define add (lambda (a b) (+ a b)))(displayln (add 2 3));; let for local bindings(let ([x 1] [y 2]) (displayln (+ x y)));; Higher-order functions(map (lambda (x) (* x x)) '(1 2 3 4))(filter even? '(1 2 3 4 5 6))(foldl + 0 '(1 2 3 4))
Lists
Core list operations.
- '(1 2 3)- Quoted list literal
- (cons 1 '(2 3))- Prepends an element, yields '(1 2 3)
- (car lst)- First element of a list
- (cdr lst)- Rest of the list after the first element
- (list 1 2 3)- Constructs a list from its arguments
- (append lst1 lst2)- Concatenates two lists
Pattern Matching
Destructuring with match.
racket
(define (describe x) (match x [(? number?) "a number"] [(list a b) (format "pair of ~a and ~a" a b)] ['() "empty list"] [_ "something else"]))(displayln (describe 5))(displayln (describe (list 1 2)))
Special Forms
Core syntactic forms.
- (define x 5)- Binds a value to a name
- (if cond then else)- Conditional expression
- (cond [test1 res1] [else default])- Multi-branch conditional
- (lambda (args) body)- Anonymous function
- (struct point (x y))- Defines a simple record type
- (let loop ([i 0]) (when (< i 5) (loop (+ i 1))))- Named let for recursion/looping
Pro Tip
Prefer match over nested cond/if for destructuring lists and structs — it makes intent explicit and catches unhandled cases more readably.
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