ErlyDTL [](https://travis-ci.org/erlydtl/erlydtl)
=======
ErlyDTL compiles Django Template Language to Erlang bytecode.
Project homepage: <https://github.com/erlydtl/erlydtl/wiki>
ErlyDTL implements the Django Template Language as documented for
version *1.6*, here:
<https://django.readthedocs.org/en/1.6.x/ref/templates/builtins.html>
Despite our best efforts to be completely compatible with the Django
Template Languge, there are still a few
[differences](https://github.com/erlydtl/erlydtl#differences-from-standard-django-template-language).
Call for maintainers
====================
My current position in life does not give me the time I feel this project deserves. So, if you feel that there are things that ought to be done, and have the skills and time to do them, please get in touch. -- @kaos
### The erlydtl branches & tags
We follow a
[gitflow](http://nvie.com/posts/a-successful-git-branching-model/)
inspired branching model, where `master` is the latest released
version (a.k.a. stable), and use `develop` for stuff that may break
from time to time.
#### master branch
Releases are made from the *master* branch, with dependency versions
pinned down and a hard coded version number in the app file.
#### develop branch
This is were all the action is, and at times may be slightly
broken. Suitable for early adopters who aren't afraid of a little
debugging and hopefully also reporting issues.
#### release tags
Whenever *master* is deemed stable with a nice set of
additions/changes, it is tagged for a new release.
As we're still going for the big 1.0 release, breaking changes **may**
be introduced also on minor release bumps; but after that, we'll stick
with [semver](http://semver.org/).
Compilation
-----------
To compile ErlyDTL, run
make
in this directory.
#### Do not use Erlang R16B03
The erl syntax tools is broken in Erlang R16B03, use R16B03-1 or any
other supported version instead.
#### Do use a recent version of rebar
In case of compilation issues, make sure your version of rebar is up-to-date.
Older versions of rebar does not support the `raw` option for dependencies, and may produce an error
message like this:
```
ERROR: Invalid dependency specification {merl,".*",
{git,
"git://github.com/erlydtl/merl.git",
"28e5b3829168199e8475fa91b997e0c03b90d280"},
[raw]}
```
Template compilation
--------------------
Usage:
```erlang
erlydtl:compile_file("/path/to/template.dtl", my_module_name)
erlydtl:compile_file("/path/to/template.dtl", my_module_name, Options)
erlydtl:compile_template("<html>{{ foo }}</html>", my_module_name)
erlydtl:compile_template("<html>{{ foo }}</html>", my_module_name, Options)
```
Result:
```erlang
{ok, Module}
{ok, Module, Warnings}
{ok, Module, Binary}
{ok, Module, Binary, Warnings}
error
{error, Errors, Warnings}
```
Options is a proplist possibly containing:
* `auto_escape` - Control automatic HTML escaping of template
values. Enabled by default.
* `binary` - Include the compiled template binary code in the result
tuple (between the module name and any warning/error lists). Note,
this option is named the same as for the Erlang compiler, with
similar use, except that this option does NOT affect whether or not
a .beam file is saved.
* `binary_strings` - Whether to compile strings as binary terms
(rather than lists). Defaults to `true`.
* `compiler_options` - Proplist with extra options passed directly to
`compiler:forms/2`. This can prove useful when using extensions to
add extra defines etc when compiling the generated code.
* `constants` - Replace template variables with a constant value when
compiling the template. This can _not_ be overridden when rendering
the template. See also `default_vars`.
* `custom_filters_modules` **deprecated** - A list of modules to be
used for handling custom filters. The modules will be searched in
order and take precedence over the built-in filters. Each custom
filter should correspond to an exported filter, e.g.
```erlang
some_filter(Value) -> iolist()
```
If the filter takes any arguments (e.g. "foo:2"), those will be
added to the call:
```erlang
some_filter(Value, Arg) -> iolist()
```
* `custom_tags_dir` - Directory of DTL files (no extension) includable
as tags. E.g. if `$custom_tags_dir/foo` contains `<b>{{ bar
}}</b>`, then `{% foo bar=100 %}` will evaluate to `<b>100</b>`.
* `custom_tags_modules` **deprecated** - A list of modules to be used
for handling custom tags. The modules will be searched in order and
take precedence over `custom_tags_dir`. Each custom tag should
correspond to an exported function with one of the following
signatures:
```erlang
some_tag(TagVars) -> iolist()
some_tag(TagVars, Options) -> iolist()
```
The `TagVars` are variables provided to a custom tag in the
template's body (e.g. `{% foo bar=100 %}` results in `TagVars =
[{bar, 100}]`). The `Options` are options passed as the second
argument to the `render/2` call at render-time. (These may include
any options, not just `locale` and `translation_fun`.)
* `debug_compiler` - Enable compiler debug diagnostics. Currently it
debug prints the options passed to `compile:forms` (i.e. if
verbosity is >= 2; that is, with two or more `verbose` options) and
enables the saving of the compiled template in source form to a .erl
file.
* `debug_info` - This option is passed to `compile:forms` to include
debug information in the compiled module.
* `debug_root` - Only applies when `debug_compiler` is `true`. The
root directory for debug source dumps. If set to `false`, no source
dump will be saved. Defaults to `undefined`, leaving the source dump
next to the source template file.
* `default_libraries` - A list of libraries that should be loaded by
default when compiling a template. Libraries can be specified either
by name (when there is a name to module mapping also provided in the
`libraries` option) or by module.
* `default_vars` - Provide default values for variables. Any value
from the render variables takes precedence. Notice: in case the
value is a `fun/0`, it will be called at compile time. See also
`constants`.
* `doc_root` - Included template paths will be relative to this
directory; defaults to the compiled template's directory.
* `extension_module` **experimental** - This is work in progress to
make erlydtl extensible.
* `force_recompile` - Recompile the module even if the source's
checksum has not changed. Useful for debugging.
* `libraries` - A list of `{Name, Module}` libraries implementing
custom tags and filters. `Module` should implement the
`erlydtl_library` behaviour (see [Custom tags and filters] below).
* `lists_0_based` - **Compatibility warning** Defaults to `false`,
giving 1-based list access, as is common practice in Erlang. Set it
to `true` to get 1-based access as in Django, or to `defer` to not
decide until render time, using the render option
`lists_0_based`. See also `tuples_0_based`.
* `locale` - Locale to translate to during compile time. May be
specified multiple times as well as together with the `locales`
option.
* `locales` - A list of locales to be passed to `translation_fun`.
Defaults to [].
* `no_env` - Do not read additional options from the OS environment
variable `ERLYDTL_COMPILER_OPTIONS`.
* `no_load` - Do not load the compiled template.
* `out_dir` - Directory to store generated .beam files. If not
specified, no .beam files will be created and a warning is
emitted. To silence the warning, use `{out_dir, false}`.
* `reader` - {module, function} tuple that takes a path to a template,
may be ReaderOptions and returns a binary with the file contents.
Defaults to `{file, read_file}`. Useful for reading templates from
a network resource.
* `reader_options` - list of {option_name, Option} that passed as the
second parameter to `reader`.
```erlang
extra_reader(FileName, ReaderOptions) ->
UserID = proplists:get_value(user_id, ReaderOptions, <<"IDUnknown">>),
UserName = proplists:get_value(user_name, ReaderOptions, <<"NameUnknown">>),
case file:read_file(FileName) of
{ok, Data} when UserID == <<"007">>, UserName == <<"Agent">> ->
{ok, Data};
{ok, _Data} ->
{error, "Not Found"};
Err ->
Err
end.
```
```
CompileResult = erlydtl:compile(Body, ModName,
[return,
{reader, {?MODULE, extra_reader}},
{reader_options, [{user_id, <<"007">>},
{user_name, <<"Agent">>}]}
]),
```
* `record_info` - List of records to look for when rendering the
template. Each record info is a tuple with the fields of the record:
```erlang
{my_record, record_info(fields, my_record)}
```
* `return` - Short form for both `return_warnings` and `return_errors`.
* `return_warnings` - If this flag is set, then an extra field
containing warnings is added to the tuple returned on success.
* `return_errors` - If this flag is set, then an error-tuple with two
extra fields containing errors and warnings is returned when there
are errors.
* `report` - Short form for both `report_warnings` and `report_errors`.
* `report_warnings` - Print warnings as they occur.
* `report_errors` - Print errors as they occur.
* `translation_fun` - A two-argument fun to use for translating
`blocktrans` blocks, `trans` tags and `_(..)` expressions at compile
time. This will be called once for each pair of translated element
and locale specified with `locales` and `locale` options. The fun
should take the form:
```erlang
fun (Block::string(), Locale|{Locale, Context}) ->
<<"ErlyDTL code">>::binary() | default
when Locale::string(), Context::string().
```
Please, keep in mind, that if your templates where not specially
designed, you probably still need render time translations.
See description of the `translation_fun` render option for more
details on the translation `context`.
Notice, you may instead pass a `fun/0`, `{Module, Function}` or
`{Module, Function, Args}` which will be called recursively until it
yields a valid translation function, at which time any needed
translation setup actions can be carried out prior to returning the
next step (either another setup function/tuple, or the translation
function).
```erlang
%% sample translation setup
fun () ->
translation_engine:init(),
fun translation_engine:translate/2
end
```
* `tuples_0_based` - **Compatibility warning** Defaults to `false`,
giving 1-based tuple access, as is common practice in Erlang. Set it
to `true` to get 1-based access as in Django, or to `defer` to not
decide until render time, using the render option
`tuples_0_based`. See also `lists_0_based`.
* `vars` **deprecated** - Use `default_vars` instead. Variables (and
their values) to evaluate at compile-time rather than
render-time.
* `verbose` - Enable verbose printing of compilation progress. Add
several for even more verbose (e.g. debug) output.
* `w` - Enable/Disable compile time checks.
Available checks:
- `non_block_tag` indicated that there is other data than `block` tags in an extends-template
(e.g. a template that begins with the `extends` tag).
* `warnings_as_errors` - Treat warnings as errors.
Helper compilation
------------------
Helpers provide additional templating functionality and can be used in
conjunction with the `custom_tags_module` option above. They can be
created from a directory of templates thusly:
```erlang
erlydtl:compile_dir("/path/to/dir", my_helper_module_name)
erlydtl:compile_dir("/path/to/dir", my_helper_module_name, Options)
```
The resulting module will export a function for each template
appearing in the specified directory. Options is the same as for
`compile/3`.
Compiling a helper module can be more efficient than using
`custom_tags_dir` because the helper functions will be compiled only
once (rather than once per template).
Notice: The exported template functions return an `iolist()` on
success only, failures are non-local (e.g. as a throw). To get the
result in wrapped tuple `{ok, iolist()} | {error, Reason}` call one of
the `render` functions: `render(Tag) | render(Tag, Vars) | render(Tag,
Vars, Opts)`.
Usage (of a compiled template)
------------------------------
### render/1
```erlang
my_compiled_template:render(Variables) -> {ok, IOList} | {error, Err}
```
Variables is a proplist, dict, gb_tree, or a parameterized module
(whose method names correspond to variable names). The variable values
can be atoms, strings, binaries, or (nested) variables.
IOList is the rendered template.
### render/2
```erlang
my_compiled_template:render(Variables, Options) -> {ok, IOList} | {error, Err}
```
Same as `render/1`, but with the following options:
* `translation_fun` - A `fun/1` or `fun/2` that will be used to
translate strings appearing inside `{% trans %}` and `{% blocktrans
%}` tags at render-time. The simplest TranslationFun would be
`fun(Val) -> Val end`. Placeholders for blocktrans variable
interpolation should be wrapped in `{{` and `}}`. In case of
`fun/2`, the extra argument is the current locale, possibly together
with a translation context in a tuple:
```erlang
fun (Val|{Val, {Plural_Val, Count}}, Locale|{Locale, Context}) ->
Translated_Val
end
```
The context is present when specified in the translation
tag. Example:
```django
{% trans "Some text to translate" context "app-specific" %}
or
{% blocktrans context "another-context" %}
Translate this for {{ name }}.
{% endblocktrans %}
```
The plural form is present when using `count` and `plural` in a
`blocktrans` block:
```django
{% blocktrans count counter=var|length %}
There is {{ counter }} element in the list.
{% plural %}
There are {{ counter }} elements in the list.
{% endblocktrans %}
```
Render time translation function is also used to translate dates.
Date tokens mimics those used in django, so you may reuse django translations.
Tokens may appear in a date are:
1. Full months names, capitalized ("January" .. "December");
2. 3 letters months names ("jan" .. "dec");
3. Associated Press style months
("Jan." .. "Dec." with "abbrev.month" context);
4. Alternative month name, for "E" option
("January" .. "December" with "alt. month" context);
5. Full week day names, capitalized ("Monday" .. "Sunday");
6. Abbreviated week day names, capitalized ("Mon" .. "Sun");
7. day time tokens ("AM", "PM", "a.m.", "p.m.", "noon", "midnight");
While date token values may be passed as lists, consider using binaries
as a default string format.
Here is a simple but robust translation function stub:
```erlang
translation_placeholder({Val,{Plural, Count}}, {L, C}) when is_list(Val) ->
translation_placeholder({list_to_binary(Val),{Plural, Count}}, LC);
translation_placeholder(Val, {L, C}) when is_list(Val) ->
translation_placeholder(list_to_binary(Val), LC);
translation_placeholder(Val, {L, C}) when is_list(C) ->
translation_placeholder(Val, list_to_binary(C));
translation_placeholder(Val, {L, C}) when is_list(C) ->
io:format("Translating ~p into ~p with context ~p~n", [Val, L, C]),
%% do nothing and return original value
Val.
```
The translation fun can also be a `fun/0`, `{Module, Function}` or
`{Module, Function, Args}` which will be called recursively until it
yields a valid translation function, at which time any needed
translation setup actions can be carried out prior to returning the
next step (either another setup function/tuple, or the translation
function).
* `lists_0_based` - If the compile option `lists_0_based` was set to
`defer`, pass this option (or set it to true, `{lists_0_based,
true}`) to get 0-based list indexing when rendering the
template. See also `tuples_0_based`.
* `locale` - A string specifying the current locale, for use with the
`translation_fun` compile-time option.
* `tuples_0_based` - If the compile option `tuples_0_based` was set to
`defer`, pass this option (or set it to true, `{tuples_0_based,
true}`) to get 0-based tuple indexing when rendering the
template. See also `lists_0_based`.
### translatable_strings/0
```erlang
my_compiled_template:translatable_strings() -> [String]
```
List of strings appearing in `{% trans %}` and `_(..)` tags.
### translated_blocks/0
```erlang
my_compiled_template:translated_blocks() -> [String]
```
List of strings appearing in `{% blocktrans %}...{% endblocktrans %}`
blocks; the translations (which can contain ErlyDTL code) are
hard-coded into the module and appear at render-time. To get a list of
translatable blocks before compile-time, use the provided
`blocktrans_extractor` module.
### source/0
```erlang
my_compiled_template:source() -> {FileName, CheckSum}
```
Name and checksum of the original template file.
### dependencies/0
```erlang
my_compiled_template:dependencies() -> [{FileName, CheckSum}]
```
List of names/checksums of templates included by the original template
file. Useful for frameworks that recompile a template only when the
template's dependencies change.
### variables/0
```erlang
my_compiled_template:variables() -> [Variable::atom()]
```
Sorted list of unique variables used in the template's body. The list
can be used for determining which variable bindings need to be passed
to the `render/3` function.
### default_variables/0
```erlang
my_compiled_template:default_variables() -> [Variable::atom()]
```
Like `variables/0`, but for any variable which have a default value
provided at compile time.
### constants/0
```erlang
my_compiled_template:constants() -> [Variable::atom()]
```
Like `default_variables/0`, but these template variables has been
replaced with a fixed value at compile time and can not be changed
when rendering the template.
Custom tags and filters
-----------------------
Starting with release *0.9.1*, the recommended way to add custom tags
and filters are to register a module implementing the
`erlydtl_library` behaviour. There are two functions needed to
implement a custom library: `version/0` and `inventory/1`.
The `version/0` function is to be able to keep backwards compatibility
in face of an evolving library behaviour, and should return the
version of the behaviour the library supports. The valid range of
versions is in the spec for the `version/0` callback in
`erlydtl_library.erl`.
### Library version 1
The `inventory/1` function is called with either `filters` or `tags`
as argument, and should return a list of all filters or tags available
in that library, respectively (see spec in `erlydtl_library.erl` for
details on syntax for this list).
Tag functions must take a list of arguments, and may take a list of
render options, and should return an `iolist()` as result value (see
`custom_tags_modules` compile option).
Filter functions must take an `iolist()` value to filter, and may take
an argument, and should return an `iolist()` as result value (see
`custom_filters_modules` compile option).
Differences from standard Django Template Language
--------------------------------------------------
* `csrf_token` The
[Cross Site Request Forgery](https://docs.djangoproject.com/en/1.6/ref/contrib/csrf/)
tag is not implemented.
* `url` The
[url](https://docs.djangoproject.com/en/1.6/ref/templates/builtins/#url)
tag is not implemented. This should be
[addressed](https://github.com/erlydtl/erlydtl/issues/115) in a
future release.
* List indexing is 1-based in erlydtl, while 0-based in Django (see
[#156](https://github.com/erlydtl/erlydtl/issues/156)).
* For an up-to-date list, see all
[issues](https://github.com/erlydtl/erlydtl/issues) marked
`dtl_compat`.
* Erlang specifics: Template variables may be prefixed with underscore
(`_`) to avoid "unused variable" warnings (see
[#164](https://github.com/erlydtl/erlydtl/issues/164)).
* `cycle` tags do not support independently moving the cycle value
from the original loop.
Tests
-----
From a Unix shell, run:
make tests
Note that the tests will create some output in tests/output in case of regressions.
License
-------
ErlyDTL is released under the MIT license.
