Recover in Prolog

Prolog allows for handling exceptions, which is similar to recovering from panics in other languages. Here’s how we can implement a similar concept:

% This predicate may throw an exception
may_throw_exception :-
    throw(error('a problem')).

% Main predicate
main :-
    % Set up exception handling
    catch(
        may_throw_exception,
        Error,
        (
            format('Recovered. Error:~n~w~n', [Error])
        )
    ),
    % This line will not be executed if an exception is thrown
    format('After may_throw_exception~n').

% Entry point
:- main.

In Prolog, we use the catch/3 predicate to handle exceptions. It takes three arguments:

1. The goal to be executed (which may throw an exception)
2. The exception to be caught
3. The handler to be executed if an exception is caught

The throw/1 predicate is used to raise an exception, similar to panic in other languages.

When you run this program, it will output:

Recovered. Error:
error(a problem)

The format/2 predicate is used for formatted output, similar to printf in other languages.

Note that in Prolog, there’s no concept of deferred execution like in some other languages. Exception handling is done through the catch/3 predicate, which encapsulates the potentially exception-throwing code.

Also, Prolog doesn’t have the concept of “not running” part of the code due to an exception, as it does in imperative languages. In Prolog, if an exception is thrown, the execution will immediately jump to the exception handler, and the rest of the predicates in the catch/3 block will not be attempted.

This example demonstrates how to handle exceptions in Prolog, which serves a similar purpose to recovering from panics in other languages. It allows your program to gracefully handle errors and continue execution rather than crashing.