Re: Why 'while' and 'repeat' loop need double block
[
Date Prev][
Date Next][
Thread Prev][
Thread Next]
[
Date Index]
[
Thread Index]
- Subject: Re: Why 'while' and 'repeat' loop need double block
- From: Roberto Ierusalimschy <roberto@...>
- Date: Wed, 9 Jan 2013 14:18:06 -0200
> When parsing 'while' and 'repeat' statement, lua uses double block
> to encapsulate the inner statement(one for 'loop').
If I remember correctly, the inner block controls the scope of variables,
while the outer block controls where to jump from a break. Consider
this code:
while 1 do
local a
x = function () return a end
end
and its opcodes:
1 [2] LOADNIL 0 0
2 [3] CLOSURE 1 0 ; 0x9f18fa0
3 [3] MOVE 0 0
4 [3] SETGLOBAL 1 -1 ; x
5 [3] CLOSE 0
6 [3] JMP -6 ; to 1
7 [4] RETURN 0 1
Roughly, the inner block ends on opcode 5, where it creates the CLOSE
instruction. The outer block ends on opcode 7, the destination of any
'break' inside the loop.
-- Roberto