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