Class: Fun

Properties:

Name	Type	Description
blocks	Array.<Block>	block stack, [0] is innermost
frameSize	number	must replace size
locals	Map	[replace] delegate to blocks
size	number	[replace] delegate to blocks
push()	function	add a block
pop()	function	end a block, maintain size
end()	function	[extend] pop last block
exit()	function	[replace] use frameSize