File

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−-- Simple template language
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−--
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−-- The new() function takes a pattern and an escape function and returns
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−-- a render() function.  Both are required.
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−--
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−-- The function render() takes a string template and a table of values.
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−-- Sequences like {name} in the template string are substituted
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−-- with values from the table, optionally depending on a modifier
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−-- symbol.
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−--
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−-- Variants are:
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−-- {name} is substituted for values["name"] and is escaped using the
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−-- second argument to new_render().  To disable the escaping, use {name!}.
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−-- {name.item} can be used to access table items.
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−-- To renter lists of items: {name# item number {idx} is {item} }
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−-- Or key-value pairs: {name% t[ {idx} ] = {item} }
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−-- To show a defaults for missing values {name? sub-template } can be used,
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−-- which renders a sub-template if values["name"] is false-ish.
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−-- {name& sub-template } does the opposite, the sub-template is rendered
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−-- if the selected value is anything but false or nil.
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−
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−local type, tostring = type, tostring;
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−local pairs, ipairs = pairs, ipairs;
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−local s_sub, s_gsub, s_match = string.sub, string.gsub, string.match;
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−local t_concat = table.concat;
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−
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−local function new_render(pat, escape, funcs)
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−	-- assert(type(pat) == "string", "bad argument #1 to 'new_render' (string expected)");
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−	-- assert(type(escape) == "function", "bad argument #2 to 'new_render' (function expected)");
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−	local function render(template, values)
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−		-- assert(type(template) == "string", "bad argument #1 to 'render' (string expected)");
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−		-- assert(type(values) == "table", "bad argument #2 to 'render' (table expected)");
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−		return (s_gsub(template, pat, function (block)
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−			block = s_sub(block, 2, -2);
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−			local name, raw, opt, e = s_match(block, "^([%a_][%w_.]*)(!?)(%p?)()");
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−			if not name then return end
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−			local value = values[name];
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−			if not value and name:find(".", 2, true) then
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−				value = values;
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−				for word in name:gmatch"[^.]+" do
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−					value = value[word];
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−					if not value then break; end
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−				end
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−			end
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−			if funcs then
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−				while opt == '|' do
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−					local f;
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−					f, raw, opt, e = s_match(block, "^([%a_][%w_.]*)(!?)(%p?)()", e);
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−					f = funcs[f];
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−					if value ~= nil and f then value = f(value); end
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−				end
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−			end
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−			if opt == '#' or opt == '%' then
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−				if type(value) ~= "table" then return ""; end
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−				local iter = opt == '#' and ipairs or pairs;
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−				local out, i, subtpl = {}, 1, s_sub(block, e);
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−				local subvalues = setmetatable({}, { __index = values });
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−				for idx, item in iter(value) do
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−					subvalues.idx = idx;
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−					subvalues.item = item;
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−					out[i], i = render(subtpl, subvalues), i+1;
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−				end
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−				return t_concat(out);
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−			elseif opt == '&' then
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−				if not value then return ""; end
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−				return render(s_sub(block, e), values);
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−			elseif opt == '~' then
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−				if value then return ""; end
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−				return render(s_sub(block, e), values);
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−			elseif opt == '?' and not value then
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−				return render(s_sub(block, e), values);
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−			elseif value ~= nil then
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−				if type(value) ~= "string" then
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−					value = tostring(value);
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−				end
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−				if raw ~= '!' then
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−					return escape(value);
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−				end
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−				return value;
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−			end
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−		end));
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−	end
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−	return render;
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−end
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−
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−return {
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−	new = new_render;
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−};