Date:         Tue, 20 Jul 2010 14:32:44 -0400
Reply-To:     Chang Chung <chang_y_chung@HOTMAIL.COM>
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:         Chang Chung <chang_y_chung@HOTMAIL.COM>
Subject:      Re: Thoughts on nested comments?
Comments: To: Mark Keintz <mkeintz@WHARTON.UPENN.EDU>

On Tue, 20 Jul 2010 17:31:17 +0000, Keintz, H. Mark
<mkeintz@WHARTON.UPENN.EDU> wrote:
...
>This is an informal request to SAS-L for thoughts on a nested comment
mechanism.  I.e. if the next sasware ballot included an item like "introduce
nested comments", how might the feature look in practice?
...
Hi, Mark:

There is this little language called Lua, which is popular among game
developers. In Lua, double dashes start a line comment that ends with the
end of line, like:
-- this is a line comment
It also has a block comment that can span multiple lines. The block comment
starts with two dashes as well, it is however immediately followed by two
left square brackets. The comment ends with *matching* two right square
brackets:
--[[
  this is a comment block
  ....
  ]]
But it is, by convention, usually written with two dashes before the closing
brackets like:
--[[
  this is a comment block
  ...
--]]
because if you do this, then *un*commenting becomes as simple as adding one
more dash at the beginning:
---[[
  this is now open
  ...
--]]
Can you see why? This is because the first line is now a line comment with
the content of "-[[", and the last line also become a line comment.

For nested comments, matching an opening to the correct closing may become a
hassle. Lua allows any number of equal signs between the two brackets, so
that you have immediate visual cues on which opening matches which ending.
something like:
--[[
  some comments
  --[=[
     some nested comments
     --[==[
     inside the nested comments
     --]==]
  --]=]
--]]
Ain't this cool? :-)
Cheers,
Chang