Panic in Scheme

In Scheme, we don’t have a direct equivalent of Go’s panic function. However, we can use Scheme’s error handling mechanisms to achieve similar functionality. We’ll use the error procedure to raise exceptions.

(import (scheme base)
        (scheme write))

(define (main)
  ; We'll use error throughout this example to check for
  ; unexpected errors. This is the only program in the
  ; example designed to raise an error.
  (error "a problem")

  ; A common use of error is to abort if a function
  ; returns an error value that we don't know how to
  ; (or want to) handle. Here's an example of
  ; raising an error if we get an unexpected error when creating a new file.
  (let ((result (with-exception-handler
                  (lambda (ex)
                    (error "File creation failed" ex))
                  (lambda ()
                    (call-with-output-file "/tmp/file" 
                      (lambda (port) 
                        (display "Hello" port)))))))
    (if (not result)
        (error "Unexpected error occurred"))))

(main)

Running this program will cause it to raise an error, print an error message, and exit with a non-zero status.

When the first error in main is raised, the program exits without reaching the rest of the code. If you’d like to see the program try to create a temp file, comment out the first error.

$ scheme panic.scm
Error: a problem

Note that unlike some languages which use exceptions for handling of many errors, in Scheme it’s common to use multiple values or specific error objects for indicating errors, and then handle them using guard expressions or exception handlers.

In this example, we’ve used error to simulate Go’s panic. The with-exception-handler is used to catch any exceptions that might occur during file creation and raise a new error if something goes wrong.

Remember that Scheme’s error handling is different from Go’s panic/recover mechanism. In Scheme, you typically use guard expressions or dynamic-wind for more controlled exception handling and cleanup.