taro
I took lessons from the last discussion and cobbled together an example as a proof-of-concept.
Mar demonstrates a Flask-like web dev interface powered by Plug on Bandit.
use Mar immediately makes a module a route. The user modules don’t need to report to an entry-point plug in the app. Library handles routing.
Normal defs defines the actions to the requests. So you can compose them Elixir way. Router matches them by their names and the HTTP methods.
defmodule MyApp do
use Mar
def get(), do: "Hello, world!"
end
path can be set. Default is "/" otherwise.
params declares allowed parameters alongside path parameters with :. Later it takes matching keys from conn.params and puts it in the actions.
Actions can return a string, a map for JSON, or a tuple being {status, headers, body}.
defmodule MyApp do
use Mar, path: "/post/:id", params: [:comment]
def get(%{id: id}) do
"You are reading #{id}"
end
def post(%{id: id, comment: comment}) do
%{
id: id,
comment: comment
}
end
def delete(%{id: _id}) do
{301, [location: "/"], nil}
end
end
Routes can interact with the library through Mar.Route protocol.
defmodule MyApp do
use Mar
def get(), do: "Hello, world!"
defimpl Mar.Route do
# Mar.Route.MyApp
def before_action(route) do
IO.inspect(route.conn.resp_body)
# => nil
route
end
def after_action(route) do
IO.inspect(route.conn.resp_body)
# => "Hello, world!"
route
end
end
end
Intention
While there are many possible approaches to helping adoption and facilitating learning, the challenge I tackle here is to nicely encapsulate Plug and reduce cognitive load for the users. @taro lacks the technical capability for something production-ready, this project waxes on top of Bandit with an escape hatch in an attempt to help you envision a light and intuitive web framework for Elixir.
The insight and guidance from the community is much appreciated:
Design
This library relies on protocol consolidation to handle routes. use Mar injects a default defimpl of Mar.Route protocol. It lists up the user modules. At the same time, defstruct saves the path as a default struct value. Then the list of implementation maps to structs, which has information for path-matching.
case Mar.Route.__protocol__(:impls) do
{:consolidated, modules} -> Enum.map(modules, &struct(&1))
:not_consolidated -> []
end
# [
# %MyApp{ path: "/", ...},
# %MyApp.Post{ path: "/post/:id/", ...}, ,
# ...
# ]
Mar.Router leaves escape hatches open with the Mar.Route protocol. The user modules redefine the functions with defimpl to access them.
# Mar.Router
def call(conn, _options) do
# Match routes, load params
route = Mar.Route.before_action(route)
# Apply action
route = Mar.Route.after_action(route)
# Send response
end
Atom keys are preferred over string keys for the sake of nicer syntax. That’s also why params need to be declared so the library can prevent dynamic atom creation.
What do you think? I’m hoping to hear from you! 
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te_chris
You got dragged a bit in the other thread but I think this really cool and a worthwhile addition to the library ecosystem
taro
Thanks for the words of encouragement!
I’m looking forward to improve upon current version and expand the project further, including zero-to-hero guides and templating.
josevalim
Hi @taro!
Thank you for exploring new directions here. If your goal is to have something smaller, may I suggest something that builds on top of functions rather than modules? Modules impose more boilerplate than functions and relying on protocol consolidation means you can’t use
Marefficiently insideMix.install/2scripts (you have to disable consolidation or use a full-blown project).Compare with the simplest hello world possible with Bandit:
There is probably a balance to be found between functions and modules here.
taro
Hi @josevalim !
Thanks for your advice. It means a lot to me.
The goal is to make it ergonomic, and not the least LoC even though I’ve got the single
.exss as the responses in the other thread.What I’m trying is to maximise the semantics of Elixir in web development. Modules are a meaningful units in Elixir, usually saved in its own file. So I wanted to put some meaning to it. A path usually has dozens of actions. That’s how I came up with module-path, function-action analogy.
Do you think this approach has a chance if the least LoC is not the goal?
That was exactly what I wanted to solve next
Is it hopeless then? I couldn’t find more information about how consolidation works under the hood and why
Mix.install/2breaks it.I want to remove the need to reporting modules to the configurations of a library or a centralised router. Is this an anti-pattern or unnatural thing in Elixir? I see many people have tried this, ending up scanning all the modules and saving them in ETS or an Agent.
dimitarvp
I am most likely not paying attention well enough here but why did you go for protocols and not behaviours? Or even functions tagged with attributes?
taro
Hi @dimitarvp !
Mar doesn’t have much to do with behaviour yet. I don’t know where to use them? I’m trying hard to remove one more thing that the user needs to do. Behaviour seems a lot of do this do that for the user. Tagging functions seems not much different. I’d appreciate it if you let me know what I can do!
Protocol is for inter-project communication. It can
Mar.Route.%MyApp{}struct.Mar.Route.MyAppNow, it removes and hides less important things. User modules don’t need to report themselves to a configuration because protocol know where they are. The library code can handle the routes polymorphically. User module can access them if they need to.
Or, I’m not seeing what your questions imply.
Is there an obviously better approach?
dimitarvp
As I said I am not even sure my question is good, it was borne out of how much I hate the
defimplblocks, they stick like sore thumbs for me.jerdew
I ran across this myself when trying something in livebook. It’s a quick add to the install line:
Mix.install([:mar], consolidate_protocols: false)This post may be helpful: Why does Livebook require `consolidate_protocols: false`
taro
I see, could you briefly share what’s wrong with them?
In Mar, I intended them to be optional escape hatches when the user module want the library to handle the route differently. You have direct access to
connin it.taro
Hi @jerdew
Thanks for the info!
The problem runs deeper than adding impls for this library though. It uses the list of consolidated modules as a registry. So it needs consolidation anyway. I thought I would find a way to reconsolidate or something. Or I have to make another way to keep modules with
use Marin one place.