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