prosody
936cf2f7531f
util/interpolation.lua

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util/interpolation.lua @ 6720:936cf2f7531f

util.interpolation: A template engine for text
author Kim Alvefur <zash@zash.se>
date Tue, 19 May 2015 15:33:20 +0200
child 6771:60957dd5b41b
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6719:0ef7a8c8fe8c 6720:936cf2f7531f
1 -- Simple template language
2 --
3 -- The new() function takes a pattern and an escape function and returns
4 -- a render() function. Both are required.
5 --
6 -- The function render() takes a string template and a table of values.
7 -- Sequences like {name} in the template string are substituted
8 -- with values from the table, optionally depending on a modifier
9 -- symbol.
10 --
11 -- Variants are:
12 -- {name} is substituted for values["name"] and is escaped using the
13 -- second argument to new_render(). To disable the escaping, use {name!}.
14 -- {name.item} can be used to access table items.
15 -- To renter lists of items: {name# item number {idx} is {item} }
16 -- Or key-value pairs: {name% t[ {idx} ] = {item} }
17 -- To show a defaults for missing values {name? sub-template } can be used,
18 -- which renders a sub-template if values["name"] is false-ish.
19 -- {name& sub-template } does the opposite, the sub-template is rendered
20 -- if the selected value is anything but false or nil.
21
22 local type, tostring = type, tostring;
23 local pairs, ipairs = pairs, ipairs;
24 local s_sub, s_gsub, s_match = string.sub, string.gsub, string.match;
25 local t_concat = table.concat;
26
27 local function new_render(pat, escape)
28 -- assert(type(pat) == "string", "bad argument #1 to 'new_render' (string expected)");
29 -- assert(type(escape) == "function", "bad argument #2 to 'new_render' (function expected)");
30 local function render(template, values)
31 -- assert(type(template) == "string", "bad argument #1 to 'render' (string expected)");
32 -- assert(type(values) == "table", "bad argument #2 to 'render' (table expected)");
33 return (s_gsub(template, pat, function (block)
34 block = s_sub(block, 2, -2);
35 local name, opt, e = s_match(block, "^([%a_][%w_.]*)(%p?)()");
36 if not name then return end
37 local value = values[name];
38 if not value and name:find(".", 2, true) then
39 value = values;
40 for word in name:gmatch"[^.]+" do
41 value = value[word];
42 if not value then break; end
43 end
44 end
45 if opt == '#' or opt == '%' then
46 if type(value) ~= "table" then return ""; end
47 local iter = opt == '#' and ipairs or pairs;
48 local out, i, subtpl = {}, 1, s_sub(block, e);
49 local subvalues = setmetatable({}, { __index = values });
50 for idx, item in iter(value) do
51 subvalues.idx = idx;
52 subvalues.item = item;
53 out[i], i = render(subtpl, subvalues), i+1;
54 end
55 return t_concat(out);
56 elseif opt == '&' then
57 if not value then return ""; end
58 return render(s_sub(block, e), values);
59 elseif opt == '?' and not value then
60 return render(s_sub(block, e), values);
61 elseif value ~= nil then
62 if type(value) ~= "string" then
63 value = tostring(value);
64 end
65 if opt ~= '!' then
66 return escape(value);
67 end
68 return value;
69 end
70 end));
71 end
72 return render;
73 end
74
75 return {
76 new = new_render;
77 };