Define

Variables

(define size 2)

Procedures

(define (cube x) (* x x x))

Lambdas

(lambda (x) (+ x 1))

; define and call
((lambda (x) (+ x 1)) 1)

; same as above, but with syntax sugar.
; defining x == 1 locally.
(let ((x 1)) (+ x 1))

; or with more local variables
(let ((x 1) (y 3)) (+ x y)) ; == 4

Pairs

Know as "tuples" in other languages, can be defined using the cons keyword which is short for "construct".

(define x (cons 1 2))

; a list
(define my_list (cons 1 (cons 2 (cons 3 4))))

The first argument can be fetched with the keyword car which is legacy from the IBM 704 days and means "Contents of Address part of Register".

TO fetch the scond argument, we use cdr which means "Contents of Decrement part of Register"

(car x)
1

(cdr x)
2

Conditionals

Here are three different options:

ccoonndd` only

(define (mod x)
  (cond
    ((> x 0) x)
    ((< x 0) (- x))
    ((= x 0) 0)
  )
)

ccoonndd` and eellssee`

(define (mod x)
  (cond
    ((< x 0) (- x))
    (else x)
  )
)

iiff` only

(define (mod x)
  (if (< x 0) (- x) x)
)

Printing

(display "hello world")
(newline)