Recover in F#

open System

// This function raises an exception.
let mayRaise () =
    raise (Exception("a problem"))

// Exception handling in F# is done using try-with expressions.
// The equivalent of Go's recover is achieved through pattern matching in the with clause.
[<EntryPoint>]
let main argv =
    try
        // This code attempts to call the function that may raise an exception.
        mayRaise ()
        
        // This code will not run if mayRaise raises an exception.
        // The execution of main stops at the point of the exception and moves to the with clause.
        printfn "After mayRaise()"
        0 // Return 0 for success
    with
    | ex ->
        // This is where we "recover" from the exception.
        // The exception details are available in the 'ex' variable.
        printfn "Recovered. Error:\n %s" ex.Message
        1 // Return non-zero for error

// Output:
// $ dotnet run
// Recovered. Error:
//  a problem

In F#, we use exceptions and try-with expressions to handle errors, which is similar to Go’s panic and recover mechanism.

The mayRaise function simulates a function that might cause an error by raising an exception. In the main function, we wrap the potentially problematic code in a try block.

The with clause acts similarly to Go’s deferred function with a recover call. It catches any exceptions that might be raised in the try block. If an exception occurs, the code in the with block is executed, allowing us to “recover” from the error and continue execution.

The pattern matching in the with clause allows us to handle different types of exceptions if needed. In this case, we’re catching all exceptions and printing the error message.

Note that in F#, we typically return an integer from the main function to indicate the program’s exit status. 0 usually means success, while non-zero values indicate an error occurred.

To run this F# program, you would typically save it in a file with a .fs extension (e.g., recover.fs), and then use the dotnet CLI to run it:

$ dotnet run
Recovered. Error:
 a problem

This demonstrates how F# can gracefully handle and recover from exceptions, allowing your program to continue execution or perform cleanup operations when errors occur.