-- extract code with tolua_hide, and also
function extract_code(fn,s)
    local code = '\n$#include "'..fn..'"\n'
    s= "\n" .. s .. "\n" -- add blank lines as sentinels
    local _,e,c,t = strfind(s, "\n([^\n]-)[Tt][Oo][Ll][Uu][Aa]_([^%s]*)[^\n]*\n")
    while e do
        t = strlower(t)
        if t == "begin" then
            _,e,c = strfind(s,"(.-)\n[^\n]*[Tt][Oo][Ll][Uu][Aa]_[Ee][Nn][Dd][^\n]*\n",e)
            if not e then
             tolua_error("Unbalanced 'tolua_begin' directive in header file")
            end
        end
        c = c.."\n"
        c = string.gsub(c, "\n[^\n]*[Tt][Oo][Ll][Uu][Aa]_[hH][iI][Dd][eE][^\n]*\n", "\n");
        c = string.gsub(c, "#define[^%(\n]*%(.-\n", "\n")
        code = code .. c
     _,e,c,t = strfind(s, "\n([^\n]-)[Tt][Oo][Ll][Uu][Aa]_([^%s]*)[^\n]*\n",e)
    end
    return code
end