RE: Closures & Recursion

["Dave Nichols" <dave.nichols@...>]

Try this:

function visit (x,v)
-- Visit potentially recursive and circular structures.
   local cv = v or visited()
   if type(x) == "string" then
     -- do something
   elseif type(x) = ... -- more types to ensure end of recursion
     -- do something
   elseif type(x) == "table" then
     if not cv(x) then
       for _, v in pairs(x) do
         visit (x,cv)
       end
     end
   end
end

Regards,

Dave Nichols
Match-IT Limited
Tel: 0845 1300 510
Fax: 0845 1300 610
mailto:dave.nichols@make247.com
http://www.make247.com

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-----Original Message-----
From: lua-bounces@bazar2.conectiva.com.br
[mailto:lua-bounces@bazar2.conectiva.com.br]On Behalf Of Stefan
Brantschen
Sent: 28 July 2006 13:24
To: Lua list
Subject: Closures & Recursion


Newbie question: I ran into the question how to use closures with
recursion -- consider this snippet:

local function visited (x)
-- Check and register if a table 'x' has been visited
   local vis = {}
   return function (x)
   for _, v in pairs(vis) do
     if x == v then return true
   end
   v[#v+1] = x
   return false
end

function visit (x)
-- Visit potentially recursive and circular structures.
   local cv = visited()
   if type(x) == "string" then
     -- do something
   elseif type(x) = ... -- more types to ensure end of recursion
     -- do something
   elseif type(x) == "table" then
     if not cv(x) then
       for _, v in pairs(x) do
         visit (x)
       end
     end
   end
end

The issue with this code is of course that each recursion call will
create a new closure ('local cv = visited()') and hence all this does
not work as intended.

What is the Correct Way to go with LUA in this case (of course
without creating globals to keep visited table -- if possible)?

Thanks and regards
- Stefan