How to Creat Executable Commands in Standard ML

Standard ML programs are often used in interactive shells(?) However, we can not only use it in an interactive shell, but also compile it to create executable commands.

To get a command name and arguments

In Standard ML, CommandLine structure provides name function and arguments. Command names and command line arguments will be obtained by them.

name function

— CommandLine.name;
val it = fn: unit -> string

CommandLine.name () yields the command name as a string.

arguments function

- CommandLine.arguments;
val it = fn: unit -> string list

CommandLine.arguments () gives command line arguments as a list of string types.

Termination process

To close the program and return to the shell, use the Process.exit function of OS structure.

- OS.Process.exit
val it = OS.Process.status -> 'a

The argument OS.Process.status is an exit status data type to pass to the shell. There are two types:

• OS.Process.success: Success (Corresponds to EXIT_SUCCESS in C)
• OS.Process.failure: Failure (Corresponds to EXIT_FAILURE in C)

To run a program

val arg = someFunc1
val _ = (someFunc2 arg; ...)

You can execute defined functions by evaluating them at the top level. The return value of functions should be discarded using an underscore or serial execution if they only use side effects.

Example

If you compile it with mlton, it becomes an executable.

(* someCommand.sml *)
val n = ref 0
fun prName () = print ("Name: \n" ^ CommandLine.name () ^ " \n")
fun prArg () = foldl (fn (z, unt) => print ((n := !n + 1; Int.toString (!n)) ^ ":" ^ z ^ " \n")) (print "Arguments: \n") (CommandLine.arguments ())
val _ = (prName (); prArg (); OS.Process.exit (OS.Process.success))

$ mlton someCommand.sml
$ ./someCommand a b c d
Name:
./someCommand
Arguments:
1: a
2: b
3: c
4: d

Reference

sml-family.org (Standard ML Main Site)