Exit in Nim

Here’s an idiomatic Nim example demonstrating the concept of exiting a program:

import os

proc main() =
  # This defer block will not be executed when using quit()
  defer:
    echo "This will not be printed!"

  echo "Exiting the program..."
  quit(3)

# In Nim, we don't need to explicitly call the main procedure
main()

This Nim program demonstrates how to exit a program with a specific status code. Here’s a breakdown of the code:

1. We import the os module, which provides the quit procedure for exiting the program.

2. We define a main procedure to encapsulate our program logic.

3. Inside main, we use a defer block. In Nim, defer is similar to Go’s defer, but it’s important to note that it won’t be executed when using quit().

4. We print a message indicating that we’re about to exit the program.

5. We call quit(3) to immediately exit the program with a status code of 3.

6. At the end of the file, we call the main procedure. In Nim, we don’t need to explicitly define a main function like in some other languages.

To run this program:

1. Save the code in a file named exit_example.nim.
2. Compile and run the program using the Nim compiler:

$ nim c -r exit_example.nim
Exiting the program...

To see the exit status:

$ nim c -r exit_example.nim
Exiting the program...
$ echo $?
3

Note that the “This will not be printed!” message never appears because the defer block is not executed when using quit().

In Nim, unlike languages like C, we don’t use an integer return value from the main function to indicate the exit status. Instead, we use the quit() procedure to exit with a specific status code.

This example demonstrates how to exit a Nim program with a custom status code and shows the behavior of defer blocks when using quit(). It’s a common pattern in Nim for handling program termination and setting exit status codes for shell scripts or other processes that might be watching the exit status of your Nim program.