[R7RS] Evaluates forms sequentially, and returns the last result(s).
Begin doesn’t introduce new scope like
let, that is,
you can’t place "internal define" at the beginning of forms
begin behaves as if forms
are spliced into the surrounding context.
For example, toplevel expression like the following is the same
as two toplevel definitions:
(begin (define x 1) (define y 2))
Here’s a trickier example:
(let () (begin (define x 2) (begin (define y 3) )) (+ x y)) ≡ (let () (define x 2) (define y 3) (+ x y))
Evaluates exp0, exp1, …, then returns the result(s)
of exp0. The name is taken from MzScheme.
This is called
prog1 in CommonLisp.
begin, this does creates a new scope,
begin0 form is expanded as follows.
(receive tmp exp0 exp1 … (apply values tmp))