Quite similar to lisp.
An advantage of s-expr:
(+ 1 2 3 4 5 6) is clearer than 1+2+3+4+5+6(fn-name args)var-name (ie, no braces)#lang ... is only a shorthand for (module name initial-import decl ...)
provide: mention list of names to export from a file
rename-out: rename names while exportingdefine-syntax:; Factorial of whole numbers
(define (fact n)
(if (<= n 0)
1
(* n {fact [- n 1]})))
let expressionslet for 'subcomputation':
Syntax:
let <list of binding> <expr>
(define foobar
(let* ([foo 10]
[bar 20])
(* foo bar)))
(define (fact n) (if (<= n 0) 1 (let* [foo (fact (- n 1))])
let* use => no recursion???
evaleval:
we can e
; assuming fact is function doing factorial
(define foo '(fact 5))
(eval foo)
; 120
We can't redefine an identifer.
(define pi 3.14)
(define pi (/ 22 7))
module: identifier already defined
∵ it's immutable.
They're bindings not value assignments.
> (quotient/remainder 17 2)
8
1
> (quotient 17 2)
8
> (remainder 17 2)
1
#t#f; pair? checks if its argument is a pair
> (pair? '())
#f
> (pair? (cons 2 3))
#t
(list 1 2 3)
; is same as
'(1 2 3)
The single quote sort of asks the interpreter to stop evaluating from that point.
listcarcdrnull or '()> (list -1 2.3 "hi")
'(-1 2.3 "hi")
> (car '(1 2 3 4 5))
1
> (cdr '(1 2 3 4 5))
'(2 3 4 5)
car and cdr for elisp is similar:
See https://docs.racket-lang.org/reference/pairs.html.
Tuples.
Immutable
Constructor: cons
1st: car
2nd element: cdr
> (cons 1 2)
'(1 . 2)
> '(1 . 2)
'(1 . 2)
> '(1 . 2 . 3)
'(2 1 3)
> (car '(1 . 2))
1
> (cdr '(1 . 2))
2
Etymology of car and cdr (for pairs and lists) in the lisp world is historical.
See https://docs.racket-lang.org/guide/for.html
(for ([i 3])
(display i))
; Above is syntactic sugar for
(for ([i (in-range 0 3)])
(display i))
; because in-range's first argument defaults to 0
racket-mode: emacs mode for racket
C-c C-c (might take a few seconds to take effect)