In my adventures on the web; I discovered an aid for writing HTML called zen-coding. Playing a bit with it, I found it lacking in some departments, and began to think that macros aren’t whats needed, but complete generation.
I remembered seeing an example of some html generating lua code a while back, and for a bit of fun decided to do my own take on it…
local function renderattributes ( attr )
local t , i = { } , 1
for k , v in pairs ( attr ) do
t [ i ] = ’ ‘
t [ i + 1 ] = k
t [ i + 2 ] = ‘=”’
t [ i + 3 ] = v
t [ i + 4 ] = ‘”’
i = i + 5
end
return table.concat ( t )
end
local function tostringtable ( t )
local r = { }
for i , v in ipairs ( t ) do
r [ i ] = tostring ( v )
end
return r
end
local elementmeta = {
__tostring = function ( t )
if #t == 0 then — Self closing tag
return “<” .. t.tag .. renderattributes ( t.attr ) .. “/>”
else
return “<” .. t.tag .. renderattributes ( t.attr ) .. “>” .. table.concat ( tostringtable ( t ) ) .. “</” .. t.tag .. “>”
end
end ;
}
local escapecodes = setmetatable (
{
[“<”] = “<” ;
[“>”] = “>” ;
[“&”] = “&” ;
[‘”’] = “"” ;
} ,
{ __index = function ( t , k ) return string.format ( “&#%03d;” , string.byte ( k ) ) end }
)
local function escapehtml ( str )
return ( str:gsub ( [=[[<>&”]]=] , escapecodes ) )
end
local stringmeta = {
__tostring = function ( t )
return escapehtml ( table.concat ( t ) )
end
}
local function construct ( tag , contents )
local attr = { }
local r = { tag = tag , attr = attr }
for k , v in pairs ( contents ) do
if type ( k ) == “string” then — attribute
assert ( type ( v ) == “string” , “Attributes must be strings” )
attr [ k ] = v
elseif type ( k ) == “number” then — Contents
if type ( v ) == “string” then
r [ k ] = setmetatable ( { v } , stringmeta )
elseif type ( v ) == “number” then
r [ k ] = setmetatable ( { tostring ( v ) } , stringmeta )
else
r [ k ] = v
end
else
error ( “Bad type” )
end
end
return setmetatable ( r , elementmeta )
end
local CDATA = function ( p ) return setmetatable ( p , { __tostring = function ( t ) return “<![CDATA[” .. table.concat ( tostringtable ( p ) ) .. “]]>” end } ) end
local javascriptblock = function ( p ) return construct ( “script” , { type=”text/javascript” ; “//” ; CDATA { ‘\n’ ; p ; ‘\n//’ } } ) end
tags = setmetatable ( {
CDATA = CDATA ;
javascriptblock = javascriptblock ;
} ,
{ __index = function ( t , k ) return function ( p ) return construct ( k , p ) end end }
)
To be used like so:
setmetatable ( _G , { __index = tags } )
print ( html {
head {
title { “Text” } ;
javascriptblock [[alert(“XHTML compatible!” );]] ;
} ;
body {
div { id=”main” ;
img { src = “blah.jpg” };
}
}
} )
Output:
<html><head><title>Text</title><script type=”text/javascript”>//<![CDATA[
alert(“XHTML compatible!” );
//]]></script></head><body><div id=”main”><img src=”blah.jpg”/></div></body></html>
The code is quite extensible, to create a new tag/block, all you need is a table with a __tostring metamethod.
Contrary to first appearances, it doesn’t just create a document from a table, but creates an internal structure of a document; which can then be generated on demand (via the recursive __tostring metamethods). This means that dynamic content can be used with the same structure:
userloggedin = function () return true end
function loggedinonly ( p ) if userloggedin() then return setmetatable ( p , { __tostring = function ( t ) return table.concat ( tostringtable ( p ) ) end } ) else return “” end end
print ( body {
loggedinonly {
div {
“Logged in!”
}
}
} )
Obviously, to facilitate writing conditional code easier, some simple helper functions can be created:
setpassthrough = function ( t ) return setmetatable ( t , { __tostring = function ( o ) return table.concat ( tostringtable ( o ) ) end } ) end
function ifcond ( cond , t , f )
if cond then
return setpassthrough ( t )
else
if f then
return setpassthrough ( f )
else
return “”
end
end
end
Maybe when I need to write some html I can put this into practice!
If you find this useful, please give me a yell!
I’m not so into this blog thing… Wonder if anyone ever even reads this stuff.
In other news; uni is always looming, hardly get any time free. Engineering mechanics is quite hard, and not the best taught subject around… Not sure how well that will come out in the end; calculus 2 is making alot more sense the second time around, probably a good thing, though it is a trudge, and I would much rather to be back in linear algebra. Engineering computation is quite easy, but I’m still getting a bit out of it, my C programming skills are less of a hodge podge, a few syntaxy things are now a heck of a lot clearer.
