Add macro to Lisp

[vinc]

• Add macro form (aliased to mac)
• Add define-macro form (aliased to def-mac)
• Add quasiquote form (aliased to `)
• Add unquote form (aliased to ,)
• Add unquote-splicing form (aliased to ,@)
• Add (function args body) for functions with multiple arguments
• Add dotted pair (a . b) equivalent to (cons a b)

[vinc]

Expanding function declaration shortcut:

> (expand (def (double x) (* x 2)))
(define double (function (x) (* x 2)))

> (def (double x) (* x 2))
double

> (double 2)
4

Expanding cond into if conditionals:

> (expand (cond (false 0) (true 1)))
(if false 0 (if true 1))

[vinc]

> (def x 'a)
x

> `(x ,x y)
(x a y)

> `(x ,x y ,(+ 1 2))
(x a y 3)

> (expand `(x ,x y ,(+ 1 2)))
(cons (quote x) (cons x (cons (quote y) (cons (+ 1 2) (quote ())))))

[vinc]

> (define set-10 (macro (x) `(set ,x 10)))
set-10

> (expand (set-10 foo))
(set foo 10)

> (define foo 42)
foo

> (set-10 foo)
foo

> foo
10

[vinc]

> (define-macro (set-10 x) `(set ,x 10)))
set-10

> (expand (define-macro (set-10 x) `(set ,x 10))))
(define set-10 (macro (x) (cons (quote set) (cons x (cons (quote 10) (quote ()))))))

[vinc]

> (define x '(1 2 3))
x

> `(+ ,x)
(+ (1 2 3))

> `(+ ,@x)
(+ 1 2 3)

[vinc]

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

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

[vinc]

And now we can have:

(define (list . args) (append args '())))

That is equivalent to:

(define list (function args (append args '())))

[vinc]

The last commit should go into another PR implementing dotted lists.