Re: What would be a good representation of XML tree as Lua tables?
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- Subject: Re: What would be a good representation of XML tree as Lua tables?
- From: nobody <nobody+lua-list@...>
- Date: 2016年8月21日 20:10:58 +0200
On 2016年08月21日 16:45, Marc Balmer wrote:
> I am working on code to easily create XML trees from Lua tables. What would,
> in your opinion, be a comfortable Lua table notation of XML trees, expressed
> as Lua tables?
I previously used the following for a quick hack: Nodes are tables,
arguments are [some_string]=value, node contents are at 2..n, and tag
name is at [1]. This looks like
{"html",
{"head",
{"title", "test document"},
{"style", type = "text/css", [[
body { max-width: 40em; margin: 2ex auto; }
]]},
},
{"body",
{"h1", class="noheader nopage", style="color: #coffee;",
"Ceci n'est pas une site web."},
}
}
and some crappy 5-minute code like this...
function unt( t )
local attr,child,out = { },{ },{ }
for k,v in pairs( t ) do
((type(k) == "number") and child or attr)[k]=v
end
local tag = table.remove( child, 1 )
-- opening tag
out[1] = "<"..tag
for k, v in pairs( attr ) do
out[#out+1] = ' '..k..'="'..v..'"'
end
out[#out+1] = ">"
-- childs, in order
for k, v in ipairs( child ) do
if type( v ) == "table" then
out[#out+1] = unt( v )
else
out[#out+1] = v
end
end
-- closing tag
out[#out+1] = "</"..tag..">"
return table.concat( out )
end
...turns it into ugly, un-indented, line break free HTML/XML.
Most annoying problems were:
* ',' after table entries: you'll probably forget it a few times
* meta/data mixed (sometimes you'd like to iterate just the
attributes but can't, so you have to manually split stuff -
allocating&freeing extra tables for temp. storage.
acceptable for a quick hack, probably slow for large stuff.
(Converting into a different representation after construction might get
rid of that...)
What works nicely:
* can add/remove/swap children
* easy traversal (just `ipairs`-loop over each node & descend)
* can test/set/unset a particular attribute
* can un/flatten subtrees
* no need for any helper code while constructing, no funcalls
(can set _ENV to empty table & load a file)
What's ugly/missing:
* hard to list/discover attributes (need to traverse & skip childs)
* no metatables anywhere (need to add after creation if needed)
* no checks at all (e.g. can insert "<script>alert(1);</script>" as
text), may need checks for templating
You might also want to experiment with pre-defined functions that create
nodes (e.g. having a 'style' function that adds the boilerplate
'type="text/css"' and just takes the style content as single argument).
This worked reasonably well for my purposes back then, but YMMV.
-- Marco