Examples

Scheme

Constructors and destructors

> (cons 1 2)
(1. 52)

> (cons 1 (list 2 3))
(1 2 3)

> (cons 1 (quote (2 3)))
(1 2 3)

> (cons (+ 1 2 3) 5)
(6 . 5)

> (cons (quote (+ 1 2 3)) 5)
((+ 1 2 3) . 5)

> (list 1 2 3)
(1 2 3)

> (car (list 1 2 3))
1

> (car (quote (1 2 3))
1

> (cdr (list 1 2 3))
(2 3)

> (cdr (quote (1 2 3)))
(2 3)

> (null? ())
True

> (null? (1))
False

> (null? (cdr (1)))
True

> (atom? 1)
True

> (atom? (list 1 2 3))
False

Define

> (define x 3)
x

> x
3

> (define (square x) (* x x))
square

> (square 4)
16

Higher order

> (define (inc x) (+ 1 x))
inc

> (map inc (list 1 2 3))
(2 3 4)

> (map inc (list 1 2 3 4))
(2 3 4 5)

Lambda

> ((lambda (x) (* x x)) 2)
4

> (map (lambda (x) (* x x)) (1 2 3 4))
(1 4 9 16)

> (map (lambda (x) (* x x)) (list 1 2 3 4))
(1 4 9 16)

> (apply + (map (lambda (x) (* x x)) (list 1 2 3 4)))
30

If

> (if (< 0 1) A B)
A

equal?

> (define a 1)
a
> (define b 1)
b
> (equal? a b)
True
> (define c 2)
c
> (equal? a c)
False

Environment

You can look up values in the environment:

> (lookup square)
[Lambda (L [Str "x"]) (L [Sym "*",Str "x",Str "x"])]

You can turn debugging on and off:

    Debug
    -----

    > (+ 1 2)
    3
    > debug
      true
    > (+ 1 2)
    PARSE: Ok (L [Sym "+",Z 1,Z 2])
    3
    > debug
    PARSE: Ok (Sym "debug")
    false
    > (+ 1 2)
    3

Something slightly more complex:

> (define (isEven n) (= (remainder n 2) 0))
isEven

> (isEven 17)
False

Running small programs

> run (define a 2);; (define b 3);; (+ a b)
5

> lookup-program earnings-totals
earnings-totals
; earnings-totals is defined in module Microscheme.Library

> my-hours
((Sym "cons" 1 20) (Sym "cons" 2 40) (Sym "cons" 1 14))
; 1h 20m, 2h 40m, 1h 14m

> (earnings-totals 20 my-hours)
(5.23 . 104.6)

; 5.23h at $20/h = $104.60

Function Dictionary

functionDict : Dict String (List Expr -> Result EvalError Expr)
functionDict =
    Dict.fromList
        [ ( "+", evalPlus )
        , ( "*", evalTimes )
        , ( "roundTo", roundTo )
        , ( "=", equalNumbers )
        , ( "<", ltPredicate )
        , ( ">", gtPredicate )
        , ( "<=", ltePredicate )
        , ( ">=", gtePredicate )
        , ( "remainder", remainder )
        ]

Arithmetic

• (+ 1 2 3 4) => 10

• (* 1 2 3 4) => 24

• (roundTo 2 3.1416) => 3.14

• (= 2 3) => False

• (< 2 3) => True

• (<= 2 3) => True

• (> 2 3) => False

• (>=2 3) => False

• (remainder 15 2) => 1