syntax for {init cond post body} {
	eval init
	while {eval cond} {
		eval body
		eval post
	}
}

def sum {n} {
	require n int
	let s 0
	for {let i 0} {< i n} {set i (+ i 1)} {
		set s (+ s i)
	}
	return s
}

println (sum 1000000)