Справка:Lua/cosmo
| ||
|---|---|---|
| Тематические статьи | ||
| Техническая справка | ||
Тэги MediaWiki: | ||
| Общие правила | ||
Справка о cosmo.
OverviewПравить
Cosmo is a "safe templates" engine. It allows you to fill nested templates, providing many of the advantages of Turing-complete template engines, without without the downside of allowing arbitrary code in the templates.
InstallationПравить
The current version of Cosmo is 16.06.04. This release adds support for Lua 5.3.
The previous version, 14.03.04, fixed a bug uncovered by a new version of LPEG. Version 13.01.30 added support for Lua 5.2. Version 10.04.06 added expressions to selectors $(\<exp\>), allowed nested [[ ]] in templates, made commas between subtemplates optional, and added a second parameter to cosmo.yield that tells Cosmo the first parameter is a literal to be included in the expansion instead of an environment.
Cosmo is installed as a rock. To install the most recent release
do luarocks install cosmo. The Cosmo rock is in the standard
repository. Installation on UNIX-based systems need the gcc toolchain.
Using CosmoПравить
Simple Form FillingПравить
Let's start with a simple example of filling a set of scalar values into a template: Here are a few examples of Cosmo in use:
values = { rank="Ace", suit="Spades" }
template = "$rank of $suit"
require("cosmo")
= cosmo.fill(template, values)
Ace of Spades
Note that the template is a string that marks where values should
go. We call a template variable like $rank a selector, and rank
is the selector's name. The table passed to cosmo.fill is the environment, and it provides the values. $rank will get replaced by value.rank ("Ace") and $suit will get replaced by value.suit ("Spades").
cosmo.fill takes two parameters at once. Cosmo also provides a
"shortcut" method f() which takes only one parameter - the template
- and returns a function that then takes the second parameter. This
allows for a more compact notation:
= cosmo.f(template){ rank="Ace", suit="Spades" }
Ace of Spades
A selector can be either a string or a Lua expression in parenthesis,
like $("foo" .. "bar") is replaced by foobar in the template. Any
variables in the expression are looked-up in the current template
environment, so $(foo) is the same as $foo, and $(rank .. suit)
would be replaced by AceSpades in the previous example.
Nested ValuesПравить
You aren't restricted to scalar values; your values can be Lua tables that you can destructure using a $val|key1|key2|...|keyn syntax. For example:
values = { cards = { { rank = "Ace" , suit = "Spades" } } }
template = "$cards|1|rank of $cards|1|suit"
= cosmo.fill(template, values)
Ace of Spades
As you can see above, you can either use numbers or strings as keys.
ArgumentsПравить
You can also pass arguments to a selector using the syntax $selector{ args }. The syntax for the argument list is the same as a Lua table constructor, but function definitions are not allowed, and you can use template selectors, which are looked up in the template environment.
If you pass an argument list and the selector maps to a function then Cosmo calls this function with the argument list as a table, and the selector expands to what the function returns. For example:
values = { message = function (arg) return arg.rank .. " of "
.. arg.suit end }
template = "$message{ rank = 'Ace', suit = 'Spades' }"
= cosmo.fill(template, values)
Ace of Spades
SubtemplatesПравить
Now, suppose we have not just one card, but several. Cosmo allows us to handle this case with "subtemplates"
mycards = { {rank="Ace", suit="Spades"}, {rank="Queen", suit="Diamonds"}, {rank="10", suit="Hearts"} }
template = "$do_cards[[$rank of $suit, ]]"
= cosmo.fill(template, {do_cards = mycards})
Ace of Spades, Queen of Diamonds, 10 of Hearts,
The subtemplate "$rank or $suit" could be enclosed in ...,
[=[...]=], [==[...]==], etc. - just like Lua's long-quoted
strings. Again, we can use the shortcut f():
= cosmo.f(template){do_cards = mycards}
Ace of Spades, Queen of Diamonds, 10 of Hearts,
Subtemplates with FunctionsПравить
If we don't have a ready table that would match the template, we can
set the value of do_cards to a function, which will yield a set of
values for the subtemplate each time it's called:
mycards = { {"Ace", "Spades"}, {"Queen", "Diamonds"}, {"10", "Hearts"} }
= cosmo.f(template){
do_cards = function()
for i,v in ipairs(mycards) do
cosmo.yield{rank=v[1], suit=v[2]}
end
end
}
Ace of Spades, Queen of Diamonds, 10 of Hearts,
You can also pass a list of arguments to this function:
template = "$do_cards{ true, false, true }[[$rank of $suit, ]]"
mycards = { {"Ace", "Spades"}, {"Queen", "Diamonds"}, {"10", "Hearts"} }
= cosmo.f(template){
do_cards = function(arg)
for i,v in ipairs(mycards) do
if arg[i] then cosmo.yield{rank=v[1], suit=v[2]} end
end
end
}
Ace of Spades, 10 of Hearts,
Finally, you can pass a literal to be included in the expansion instead of an environment. An example:
template = "$do_cards{ true, false, true }[[$rank of $suit]]"
mycards = { {"Ace", "Spades"}, {"Queen", "Diamonds"}, {"10", "Hearts"} }
= cosmo.f(template){
do_cards = function(arg)
local n = #mycards
for i,v in ipairs(mycards) do
cosmo.yield{rank=v[1], suit=v[2]}
if i < n then cosmo.yield(", ", true) end
end
end
}
Ace of Spades, Queen of Diamonds, 10 of Hearts
Alternative SubtemplatesПравить
In some cases we may want to use differente templates for different
items in the list. For example, we might want to use a different
template for the first and/or last item, or to use different templates
for odd and even numbers. We can do this by specifying several
templates, separated by a comma. In that case, cosmo will use the
first template in the sequence, unless the table of values for the
item contains a special field _template, in which case this field
will be used as an index into the list of alternative templates. For
instance, setting _template to 2 would tell cosmo to use the 2nd
template for this item.
table.insert(mycards, {"2", "Clubs"})
template = "You have: $do_cards[[$rank of $suit]],[[, $rank of $suit]],[[, and $rank of $suit]]"
= cosmo.f(template){
do_cards = function()
for i,v in ipairs(mycards) do
local t
if i == #mycards then -- for the last item use the third template
t = 3
elseif i~=1 then -- use the second template for items 2...n-1
t = 2
end
cosmo.yield{rank=v[1], suit=v[2], _template=t}
end
end
}
You have: Ace of Spades, Queen of Diamonds, 10 of Heards, and 2 of Clubs
Note that the first item is formatted without preceeding ", ", while the last item is preceeded by an extra "and".
Deeper NestingПравить
Templates and subtemplates can be nested to arbitrary depth. For instance, instead of formatting a set of cards, we can format a list of sets of cards:
players = {"John", "Joao"}
cards = {}
cards["John"] = mycards
cards["Joao"] = { {"Ace", "Diamonds"} }
template = "$do_players[[$player has $do_cards[[$rank of $suit]],
[[, $rank of $suit]],[[, and $rank of $suit]]\n]]"
= cosmo.f(template){
do_players = function()
for i,p in ipairs(players) do
cosmo.yield {
player = p,
do_cards = function()
for i,v in ipairs(cards[p]) do
local t
if i == #mycards then
t = 3
elseif i~=1 then -- use the second template for items 2...n-1
t = 2
end
cosmo.yield{rank=v[1], suit=v[2], _template=t}
end
end
}
end
end
}
John has Ace of Spades, Queen of Diamonds, 10 of Hearts, and 2 of Clubs
Joao has Ace of Diamonds
ScopeПравить
Subtemplates can see values that were set in the higher scope:
template = "$do_players[[$do_cards[[$rank of $suit ($player), ]]]]"
= cosmo.f(template){
do_players = function()
for i,p in ipairs(players) do
cosmo.yield {
player = p,
do_cards = function()
for i,v in ipairs(cards[p]) do
cosmo.yield{rank=v[1], suit=v[2]}
end
end,
}
end
end
}
Ace of Spades (John), Queen of Diamonds (John), 10 of Hearts (John), 2 of Clubs (John), Ace of Diamonds (Joao),
Note that in this case the field "player" is set in the table of
values that is passed to do_players, but is used one level deeper -
in do_cards.
The scoping behavior can be overriden by setting a metatable on the environment you pass to the subtemplates.
IfПравить
Subtemplates and arguments let you implement a more generic conditional:
template = "$do_players[=[$player: $n card$if{ $plural }[[s]]
$if{ $more, $n_more }[[(needs $2 more)]],[[(no more needed)]]\n]=]"
= cosmo.f(template){
do_players = function()
for i,p in ipairs(players) do
cosmo.yield {
player = p,
n = #cards[p],
["if"] = function (arg)
if arg[1] then arg._template = 1 else arg._template = 2 end
cosmo.yield(arg)
end,
plural = #cards[p] > 1,
more = #cards[p] < 3,
n_more = 3 - #cards[p]
}
end
end
}
John: 4 cards (no more needed)
Joao: 1 card (needs 2 more)
The conditional above is already present in Cosmo as cosmo.cif. Expressions in arguments
make it more useful:
template = "$if{ math.fmod(x, 4) == 0, target = 'World' }[[ Hello $target! ]],
[[ Hi $target! ]]"
result = cosmo.fill(template, { math = math, x = 2, ["if"] = cosmo.cif })
assert(result == " Hi World! ")
Other conditionalsПравить
In some cases we want to format an set of values if some condition
applies, and cosmo.if is not enough.
This can be done with a function and a subtemplate by just
replacing a for-loop with an if-block. However, since this is a
common case, cosmo provides a function for it:
template = "$do_players[[$player: $n card$if_plural[[s]] $if_needs_more[[(needs $n more)]]\n]]"
= cosmo.f(template){
do_players = function()
for i,p in ipairs(players) do
cosmo.yield {
player = p,
n = #cards[p],
if_plural = cosmo.cond(#cards[p] > 1, {}),
if_needs_more = cosmo.cond(#cards[p] < 3, { n = 3 - #cards[p] })
}
end
end
}
John: 4 cards
Joao: 1 card (needs 2 more)
Like fill(), cond() has a "shortcut" equivalent which takes only
one parameter (the template) and returns a function:
= cosmo.f(template){
do_players = function()
for i,p in ipairs(players) do
cosmo.yield {
player = p,
n = #cards[p],
if_plural = cosmo.c(#cards[p] > 1){},
if_needs_more = cosmo.c(#cards[p] < 3){ n = 3-#cards[p] }
}
end
end
}
John: 4 cards
Joao: 1 card (needs 2 more)
Map and InjectПравить
Cosmo provides two convenience functions for writing simple templates, cosmo.map
and cosmo.inject. Both functions have to be passed in a template's environment.
The cosmo.map function yields each of its arguments in sequence, and inject yields
its whole argument table. A simple example:
template = "<ol>\n$map{ 'Spades', 'Hearts', 'Clubs', 'Diamonds'}[[<li>$it</li>\n]]</ol>"
= cosmo.fill(template, { map = cosmo.map })
<ol>
<li>Spades</li>
<li>Hearts</li>
<li>Clubs</li>
<li>Diamonds</li>
</ol>
template = "$inject{ suit = 'Spades' }[[Ace of <b>$suit</b>]]"
= cosmo.fill(template, { inject = cosmo.inject })
Ace of <b>Spades</b>
ConcatПравить
Putting a delimiter between each expansion of a subtemplate is so
common that Cosmo provides also provides a convenience function for
it, cosmo.concat. This is an example:
template = "$concat{ cards, ', ' }[[$1 of $2]]"
mycards = { {"Ace", "Spades"}, {"Queen", "Diamonds"}, {"10", "Hearts"} }
= cosmo.f(template){
cards = mycards,
concat = cosmo.concat
}
Ace of Spades, Queen of Diamonds, 10 of Hearts
API ReferenceПравить
cosmo.compile(template, chunkname)- compiles
templateinto a function that takes an environment and returns the filled template. Assignschunknameas the name of this function cosmo.fill(template, env)- same as
cosmo.compile(template)(env) cosmo.yield(env, is_literal)- fills the current subtemplate with
envifis_literalisnilorfalseand adds it to the output stream; otherwise adds the the stringenvto the output stream cosmo.cond(bool, tab)- returns a function that yields an empty environment if
boolisnilorfalseandtabotherwise cosmo.c(bool)- returns a function that takes a table
taband does the same thing ascosmo.cond(bool, tab) cosmo.map{ ... }- has to be used inside a template; yields each element of its argument in turn
cosmo.inject(env)- has to be used inside a template; yields its argument
cosmo.cif{ exp, ... }- has to be used inside a template; yields its argument to subtemplate 2 if
expisnilorfalseand to subtemplate 1 otherwise cosmo.concat{ list, [delim] }- has to be used inside a template; for each element of
listyields it and, if it is not the last, yields the literaldelimor ", " isdelimisnil
Contact UsПравить
For more information please contact one of the authors, Fabio Mascarenhas and Yuri Takhteyev, or write to the Sputnik Mailing List.
Comments are welcome!
LicenseПравить
Cosmo is free software: it can be used for both academic and commercial purposes at absolutely no cost. There are no royalties or GNU-like "copyleft" restrictions. Cosmo qualifies as Open Source software. Its licenses are compatible with GPL. The legal details are below.
The spirit of the license is that you are free to use Cosmo for any purpose at no cost without having to ask us. The only requirement is that if you do use Cosmo, then you should give us credit by including the appropriate copyright notice somewhere in your product or its documentation.
The original Cosmo library is designed and implemented by Yuri Takhteyev, with much feedback and inspiration by Andre Carregal. This version is a reimplementation by Fabio Mascarenhas, with aditional features. The implementations are not derived from licensed software.
Copyright © 2008-2014 Fabio Mascarenhas. Copyright © 2007-2008 Yuri Takhteyev.
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.