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Anaphora

Anaphora is the anaphoric macro collection for Elixir. An anaphoric macro is one that deliberately captures a variable (typically it) from forms supplied to the macro.

Getting Started

• Add the Anaphora dependency to your mix.exs file:

def deps do
  [{:anaphora, "~> 0.1.2"}]
end

• After you are done, run mix deps.get in your shell.

Provided API

alet

alet is basic anaphoric macro. It's not very useful in user code but other anaphoric macros are built on top of it. alet binds result of the expression to the it variable (via case) in the scope of the body:

defmodule User do
  use Anaphora

  ...
  def user_email(user_id) do
    alet fetch_user(user_id) do
      if it, do: it.email, else: raise "Failed to fetch user"
    end
  end
end

aif

Works like if, except that result of the condition is bound to it (via alet) for the scope of the then and else clauses:

defmodule User do
  use Anaphora

  ...
  def user_email(user_id) do
    aif fetch_user(user_id), do: it.email, else: raise "Failed to fetch user"
  end
end

acond

Works like cond, except that result of each condition is bound to it (via alet) for the scope of the corresponding body:

defmodule Notification do
  use Anaphora

  ...
  def send_notification(user, message) do
    acond do
      user.email -> send_notification_by_email(it, message)
      user.phone -> send_notification_by_sms(it, message)
      :else -> raise "Unable to send notification"
    end
  end
end

acase

Works like case, except that result of the key expression is bound to it (via alet) for the scope of the cases.

afn

Works like fn, except that anonymous function is bound to it (via blood magic) for the scope of the function body:

import Anaphora

in_order_tree_traversal = afn do
  {left, center, right}, callback ->
    it.(left, callback)
    callback.(center)
    it.(right, callback)
  nil, _ -> nil
end

in_order_tree_traversal.({{nil, 1, nil}, 2, {nil, 3, {nil, 4, nil}}}, &IO.puts/1)
# => 1, 2, 3, 4

warning: Invocation of it takes a lot of time. Don't use afn in performance critical code. It will be fixed after Elixir 1.0 release.

aand

Evaluates each clause one at a time and binds result to it. As soon as any clause evaluates to nil (or false), aand returns nil without evaluating the remaining clauses. If all clauses but the last evaluate to true values, aand returns the results produced by evaluating the last clause:

defmodule Notification do
  use Anaphora

  ...
  def send_email_to_user(user_id, message) do
    aand do
      fetch_user(user_id)
      it.email
      send_email(it, message)
    end || raise "Unable to send email"
  end
end

License

Anaphora source code is released under The MIT License. Check LICENSE file for more information.