To set up a basic Erlang project structure, you typically follow these steps:
- Start by creating a root directory for your project. Choose a meaningful name for your project and create a new directory with that name.
- Inside the project's root directory, create a few important subdirectories to organize your code and other project files. Here are some common directories you may include: /src: This directory holds your Erlang source code files. It's where you'll write the modules that make up your project. /include: If your project includes any header files or include files, you can place them in this directory. /test: This directory is used for storing test files. It typically contains unit tests or other test-related code. /deps: If your project depends on any external libraries or dependencies, you can place them in this directory. /doc: This directory can be used to store project documentation, such as API documentation or other related materials.
- It's common practice to have a file named rebar.config or rebar3.config at the project's root directory. This file is used to define project-specific settings and dependencies. If you're using a build tool like Rebar or Rebar3, you may need to specify the necessary project details in this file.
- Start adding your Erlang source code files inside the /src directory. Each source file should have a .erl extension and corresponds to an Erlang module. Name your files and modules based on their functionality and purpose.
- If you decide to include tests, create test files inside the /test directory. Test files typically have a .erl extension as well and follow the naming convention of the module being tested but with a _test suffix.
- As you develop your project, organize additional files (such as documentation, configuration files, or resources) within their respective directories.
Remember, project structures can vary based on personal preference or specific requirements. It's important to maintain consistency and clearly organize your project files to ensure maintainability and ease of collaboration.
Best Erlang Books to Read in 2024
How to set up a basic Erlang project structure?
To set up a basic Erlang project structure, you can follow these steps:
- Create a project directory: Open your terminal or command prompt and navigate to the location where you want to create your project. Create a new directory for your Erlang project using the mkdir command. For example, mkdir my_erlang_project.
- Create a source code directory: Within the project directory, create a directory to hold your Erlang source code files. Conventionally, this directory is named src. Use the mkdir command to create it. For example, mkdir src.
- Create a rebar.config file: Rebar is a build and dependency management tool for Erlang projects. Create a rebar.config file in the project directory using a text editor. This file contains project-specific build configuration and dependency information. An example of a minimal rebar.config file is:
1
|
{deps_dir, "deps"}.
|
- Create an application file: In the src directory, create a module file for your application. Conventionally, the module is named after your project and its first letter is capitalized. For example, my_erlang_project.erl. This file will contain the main entry point for your application.
- Implement the application: Open the my_erlang_project.erl file in a text editor and define your application logic. For a basic structure, follow the OTP (Open Telecom Platform) principles and implement it as an OTP application. This includes defining the start/2 and init/1 functions.
- Compile the code: Open your terminal or command prompt and navigate to the project directory. Use the Erlang compiler (erlc) to compile your source code files. For example, erlc -o ebin src/*.erl. This command will compile all Erlang source files in the src directory and place the compiled beam files in the ebin directory.
- Create a release directory (optional): If you want to create a standalone release of your Erlang application, you can create a rel directory in your project folder. This directory will hold all the necessary files for running your application independently.
That's it! You have now set up a basic Erlang project structure. You can continue developing your application by adding more modules, dependencies, and tests as needed.
What is a supervisor in Erlang?
In Erlang, a supervisor is a process that is responsible for monitoring and managing other processes, called worker processes, within an Erlang application. The supervisor's main task is to ensure the overall health and integrity of the application by monitoring the worker processes and taking appropriate actions in case of failures.
Supervisors define a hierarchical structure for process management, where they supervise a group of worker processes. The supervisor can restart a failed worker process, start new processes if required, or terminate the entire application if necessary.
The supervisor uses a predefined restart strategy to handle failures, which determines the actions to be taken in response to different types of failures, such as temporary errors, permanent errors, or child process termination. The supervisor can also define dependencies between processes, specifying the order in which they should be started or restarted.
Supervisors are a fundamental part of Erlang's OTP (Open Telecom Platform) design principles, which help in building reliable and fault-tolerant systems.
How to create an Erlang application?
To create an Erlang application, follow these steps:
- Set up your Erlang development environment by installing the Erlang programming language and its runtime system.
- Create a new directory for your application.
- Inside the directory, create the following folders: src, include, and ebin.
- In the src folder, create a new Erlang module file with a .erl extension. For example, create a file called my_app.erl.
- Implement the necessary functions in your module to define the behavior of your application. For example, you can define a start/0 function to start your application.
- In the include folder, create header files for your modules if necessary. Header files use the .hrl extension.
- Compile your Erlang module(s) using the Erlang compiler. Open a terminal, navigate to the root directory of your application, and run the following command: erlc -o ebin src/*.erl
- If your application has dependencies on other libraries or Erlang applications, you can specify them in a rebar.config file located in the root directory. The rebar.config file allows you to easily manage dependencies and compile your application with the appropriate options.
- Once your application is compiled, you can start the Erlang shell by running the erl command in the terminal. In the Erlang shell, you can call the functions defined in your application for testing purposes.
- If your application needs to run continuously, you can start it as a standalone Erlang node using the command erl -sname my_app -pa ebin. This will start your application and allow it to receive and process messages.
Remember to organize your application's code into modules and functions based on the desired functionality. Use Erlang's message passing and concurrency features to build fault-tolerant and distributed systems.
How to set up a supervisor process in Erlang?
To set up a supervisor process in Erlang, follow these steps:
- Create a new Erlang module and define it as a supervisor process. You can use the supervisor behavior from the supervisor module. For example:
1 2 3 4 5 6 7 8 9 10 11 |
-module(my_supervisor). -behaviour(supervisor). %% Implement the supervisor callback functions -export([init/1]). init(_Args) -> %% Define the supervision strategy and child processes {ok, {{one_for_one, 5, 10}, [ %% Define child processes here ]}}. |
- Implement the init/1 callback function to define the supervision strategy and child processes.
The supervision strategy specifies how the supervisor should handle the child processes. Common strategies include one_for_one (restarts only the failed child process), one_for_all (restarts all child processes if one fails), and rest_for_one (restarts only the failed child process and all processes that were started after it).
- Define the child processes within the list of child specifications in the init/1 function. Each child specification is a tuple that includes the child process type and its initialization arguments.
For example, to create a child and start a gen_server process, you can use the worker function:
1
|
{worker, {my_server, start_link, []}, permanent, 5000, worker, [my_server]}.
|
In this example, my_server is the module that implements the gen_server behavior.
- Start the supervisor process using the supervisor:start_link/2 function. Pass the supervisor module and its initialization arguments to the function.
For example, to start the supervisor defined in my_supervisor:
1
|
supervisor:start_link({local, my_supervisor}, []).
|
This creates and starts the supervisor process.
Note: Make sure to define the child processes correctly in the supervisor module to ensure they can be managed and restarted by the supervisor.
How to create a gen_server in Erlang?
To create a gen_server in Erlang, you can follow these steps:
- Define the module: Start by creating a new module that defines your gen_server. This can be done by creating a new .erl file in your project directory.
- Include the necessary dependencies: In the module, include the necessary libraries and modules by adding the following line at the beginning of the file:
1 2 |
-module(my_gen_server). -behaviour(gen_server). |
- Implement the callbacks: Next, implement the required callbacks for the gen_server behavior. These include init/1, handle_call/3, handle_cast/2, and handle_info/2. For example:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 |
-export([start/0]). start() -> gen_server:start_link({local, ?MODULE}, ?MODULE, [], []). init([]) -> {ok, []}. handle_call(get_data, _From, State) -> {reply, State, State}. handle_cast(set_data, State) -> {noreply, [{data, some_value} | State}]. handle_info(_Info, State) -> {noreply, State}. |
- Define the public API: Optionally, define a public API to interact with the gen_server. This can include functions like start/0 to start the server and other functions to handle specific calls or casts. For example:
1 2 3 4 5 6 7 |
-export([start/0, get_data/0]). start() -> gen_server:start_link({local, ?MODULE}, ?MODULE, [], []). get_data() -> gen_server:call({local, ?MODULE}, get_data). |
- Start and interact with the gen_server: Finally, start the gen_server by calling my_gen_server:start() (assuming the module name is "my_gen_server"). Then, you can interact with the gen_server by calling the defined public API functions, such as my_gen_server:get_data().
This is a basic outline of how to create a gen_server in Erlang. You can further customize and add more functionality based on your specific requirements.
How to implement callback functions in Erlang?
In Erlang, callback functions can be implemented by defining a module that exports the necessary callback functions and passing the module as an argument to the function that requires the callbacks. Here's an example of how to implement and use callback functions in Erlang:
- Define the callback module:
1 2 3 4 5 6 |
-module(callback_module). -export([callback_function/1]). callback_function(Data) -> %% Do something with the data io:format("Callback function called with data: ~p~n", [Data]). |
- Implement the function that requires a callback:
1 2 3 4 5 6 7 8 |
-module(main_module). -export([do_something/2]). do_something(Data, CallbackModule) -> %% Perform some task io:format("Doing something with data: ~p~n", [Data]), %% Call the callback function CallbackModule:callback_function(Data). |
- Run the code:
1 2 3 |
1> c(callback_module). 2> c(main_module). 3> main_module:do_something("example", callback_module). |
This will output:
1 2 |
Doing something with data: "example" Callback function called with data: "example" |
Note that in this example, the callback function callback_function/1 is defined in the callback_module and passed as an argument to do_something/2 function in main_module. The do_something/2 function then calls the callback function. You can define multiple callback functions in the callback module and pass different callback modules to the main function based on your requirements.
