Execing Processes in Standard ML

Here’s the translation of the Go code to Standard ML, along with explanations in Markdown format suitable for Hugo:

Our example demonstrates how to replace the current process with another one using Standard ML. This is similar to the exec function in Unix-like systems.

structure Exec = struct
  (* For our example, we'll exec 'ls'. *)
  fun execLs () =
    let
      (* Find the absolute path to the 'ls' binary *)
      val binary = "/bin/ls"
      
      (* Prepare arguments for 'ls' *)
      val args = ["ls", "-a", "-l", "-h"]
      
      (* Get the current environment *)
      val env = Posix.ProcEnv.environ()
      
      (* Execute the 'ls' command *)
      val _ = Posix.Process.exec (binary, args, env)
    in
      (* If exec succeeds, this code is never reached *)
      OS.Process.exit OS.Process.failure
    end
end

val _ = Exec.execLs()

In this Standard ML code:

1. We define a structure Exec to encapsulate our functionality.

2. The execLs function is where the main logic resides:

   • We hardcode the path to the ls binary as “/bin/ls”. In a real-world scenario, you might want to use a function to find the binary’s path.
   • We prepare the arguments for ls in a list format.
   • We retrieve the current environment using Posix.ProcEnv.environ().
   • We use Posix.Process.exec to replace the current process with the ls command.

3. If the exec call is successful, the current process is replaced, and no further Standard ML code is executed.

4. If exec fails, the code will continue to the OS.Process.exit call, terminating the program with a failure status.

5. Finally, we call Exec.execLs() to run our function.

To run this program:

$ sml exec_ls.sml
total 16
drwxr-xr-x  4 user  136B Oct 3 16:29 .
drwxr-xr-x 91 user  3.0K Oct 3 12:50 ..
-rw-r--r--  1 user  1.3K Oct 3 16:28 exec_ls.sml

Note that Standard ML doesn’t have a direct equivalent to Go’s goroutines or Java’s threads. Concurrency in Standard ML is typically handled through other mechanisms, such as Concurrent ML (CML) which provides first-class synchronous operations and events.

Remember that this example assumes you’re running on a Unix-like system with access to the ls command. The exact output may vary depending on your system and directory contents.