Recover in Erlang

In Erlang, we can use the concept of “try-catch” to handle exceptions, which is similar to recovering from panics in other languages. Here’s an example of how to implement this:

-module(recover).
-export([main/0]).

% This function throws an exception.
may_throw() ->
    throw("a problem").

main() ->
    % We use a try-catch block to handle exceptions
    try
        may_throw(),
        % This code will not run because may_throw() throws an exception
        io:format("After may_throw()~n")
    catch
        % The catch clause will handle the exception
        Error:Reason ->
            io:format("Recovered. Error:~n~p~n", [Reason])
    end.

In Erlang, we use throw/1 to raise an exception, which is similar to panicking in other languages. The try-catch block is used to handle exceptions, which is analogous to using defer and recover in some other languages.

The may_throw/0 function throws an exception with the message “a problem”.

In the main/0 function:

1. We wrap the potentially exception-throwing code in a try block.
2. The catch clause is used to handle any exceptions that might be thrown.
3. If an exception is caught, we print a message along with the reason for the exception.

This structure allows us to handle exceptions and continue execution, rather than letting the exception crash the entire program.

To run this program:

$ erlc recover.erl
$ erl -noshell -s recover main -s init stop
Recovered. Error:
"a problem"

In this example, the code after may_throw() in the try block doesn’t execute because an exception is thrown. Instead, execution jumps to the catch clause, which handles the exception and allows the program to continue running.

This demonstrates how Erlang’s exception handling can be used to recover from errors and maintain program execution, similar to recovering from panics in other languages.