Jade

The Racket Guide

Guide link

About the language

  • Racket is a dialect of the Lisp language and a direct descendant of Scheme
  • Consists of the racket compiler, interpreter and runtime and raco build and package manager

Values and Definitions

; Values
123
#t
"Hello World"
 
; Definition
(define a 5)           ; Variable
(define (extract str)  ; Procedure
	(substring str 1 3))
(define (extract str)  ; Multi body procedure
	(printf "Substring")
	(substring str 1 3))
(define (extract str)
	substring str 1 3)  ; Always returns 3 due to lack of ()
(define (double v)      ; Procedure application on expressions
	((if (string? v) string-append +) v v))
 
; Anonymous procedures/functions
(lambda (s) (string-append s "!"))
 
; Procedure application 
(extract "Hello")  ; el
 
; Program module definition
#lang racket <topform>
  • Values include numbers, booleans, strings and byte strings
  • Program module definition starts with a #lang, followed by the language and then a topform which can be either a expression or definition
  • Definitions can be of two types
    • (define <id> <expr>) - binds result of expr to id
    • (define (<id> <id>*) <definition>* <expr>+) - binds first <id> to a procedure with the rest being arguments. <expr> is the body of the function
  • Under the hood, the fn defn is the same as a non fn, it is just a value
  • For a multi expression body, the last expression is the result whereas the remaining are evaluated, usually for side effects.
  • Procedure application syntax - (<expr> <expr>*) wherein the first expr is usually an id but can also be an expr that evaluates to a procedure
  • Lambdas
    • (lambda (<id>*) <definition>* <expr>+)
    • Anonymous functions and are also closures due to Racket being a lexically scoped language

Conditionals

; if (an if else)
(if (> a b)
	"a > b"
	"a < b")
 
; cond (a switch case)
(cond
	[(string-prefix? s "a")
	 "a first"]
	[(string-prefix? s "b")
	 "b first"]
	[else "dunno"])
  • (if <expr> <expr> <expr>) The first expr is always evaluated and if it is true, the second is evaluated, else, the third.
    • if can be nested to create complex conditions
    • (and|or <expr>+) can also be used
  • (cond) is used as a if-else chain. The [] are convention, they are interchangeable with ()

Local bindings

Useful definitions

(enter! "file_name")
  • enter! loads code from the file and switches the evaluation context to the inside of the module.
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