# EEl - Embedded Erlang - template renderer (WIP)

**URL:** <https://erlangforums.com/t/eel-embedded-erlang-template-renderer-wip/1827>\
**Category:** Libraries\
**Tags:** embedded-erlang, eel\
**Created:** [September 8, 2022, 7:20am UTC](https://erlangforums.com/t/eel-embedded-erlang-template-renderer-wip/1827 "2022-09-08T07:20:19Z")\
**Posts on this page:** 1\
**Showing post:** 9

<div class="post-metadata">

**Author:** ![williamthome](https://erlangforums.com/user_avatar/erlangforums.com/williamthome/32/471_2.png) [@williamthome](https://erlangforums.com/u/williamthome)\
**Post date:** [May 27, 2023, 4:24am UTC](https://erlangforums.com/t/eel-embedded-erlang-template-renderer-wip/1827/9 "2023-05-27T04:24:21Z")

</div>

Ok, I’m here again after a while to talk about this lib called [EEl](https://github.com/williamthome/eel).  
Just merged a new code, I rewrote everything from scratch.  
The idea is the same, but now it’s more simple and more versatile.  
There is now the possibility to define a custom engine using the [eel\_engine](https://github.com/williamthome/eel/blob/main/src/eel_engine.erl) behavior. The default one is the [eel\_smart\_engine](https://github.com/williamthome/eel/blob/main/src/eel_smart_engine.erl). The job of the engine is to convert the code into [AST](https://www.erlang.org/doc/apps/erts/absform.html) (Abstract Syntax Tree).

> Compare the [eel\_smart\_engine](https://github.com/williamthome/eel/blob/main/src/eel_smart_engine.erl#L56) implementation to a [simple engine](https://github.com/williamthome/eel/blob/main/src/eel_tokenizer.erl#L270) used for tests.

See the [README](https://github.com/williamthome/eel/tree/main#readme) for more details, but in a nutshell, strings and files can be compiled and evaluated to binary. For example, using a simple binary as the template:

```erlang
1> eel:eval(<<"Hello, <%= Name .%>!">>, #{'Name' => <<"World">>}).
[<<"Hello, ">>,<<"World">>,<<"!">>]

```

or compiling it to a module

```erlang
1> eel:compile_to_module(<<"Hello, <%= Name .%>!">>, foo).
{ok,foo}
2> foo:eval(#{'Name' => <<"World">>}).
[<<"Hello, ">>,<<"World">>,<<"!">>]

```

or using the [eel](https://github.com/williamthome/eel/blob/main/src/eel.erl) module functions.

Taking the module example, the is a render function that gives this result:

```erlang
3> foo:render(#{'Name' => <<"World">>}).
{[<<"Hello, ">>,<<"World">>,<<"!">>],
 #{ast =>
       [{2,
         {{1,8},
          [{call,1,
               {remote,1,{atom,1,eel_converter},{atom,1,to_binary}},
               [{'fun',1,
                    {clauses,[{clause,1,[],[],[{var,1,'Name'}]}]}}]}]}}],
   bindings => #{'Name' => <<"World">>},
   changes => [{2,<<"World">>}],
   dynamic => [{2,{{1,8},<<"World">>}}],
   static => [{1,{{1,1},<<"Hello, ">>}},{3,{{1,20},<<"!">>}}],
   vars => [{2,['Name']}]}}

```

It returns a tuple with the binary and a metadata that I called `snapshot`. See for what the snapshot is useful by looking at the [example](https://github.com/williamthome/eel/tree/main#example) in the docs, but basically, it holds information to prevent the need to recompile and gives the information to only evaluate what changed.

> Note about the key of the bindings/variables passed to render/eval. Is totally fine to write keys in `snake_case` like `#{name => <<"World">>}` instead of `#{'Name' => <<"World">>}`, or better, `#{ThisIsFine => ok}` can be write as `#{this_is_fine => ok}`.

From time to time I see people asking about Erlang for Web Development or what framework to use. I believe this lib can help in some manner.

Just a side note writing the template directly in an Erlang module, e.g.

```erlang
foo() ->
    eel:compile(<<\"
        You need to \"escape\" all \"quoted texts\" inside this binary.
        Also, you will have some indentation issues.
    \">>).

```

[This recent proposal](https://erlangforums.com/t/feature-heredocs-triple-quoted-text/2638) can help to write better multi-line texts.

Disclaimer: It is still a WIP. There are few docs, specs and tests.

And that’s it.  
Suggestions welcome.

All the best,  
William

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