Printing only print output with SML/NJ

Question

I'm trying to use SML/NJ, and I use sml < source.sml to run the code, but it prints out too much information.

For example, this is the source.sml:

fun fac 0 = 1
  | fac n = n * fac (n - 1)
val r = fac 10 ;
print(Int.toString(r));

This is the output:

Standard ML of New Jersey v110.77 [built: Tue Mar 10 07:03:24 2015]
- val fac = fn : int -> int
val r = 3628800 : int
[autoloading]
[library $SMLNJ-BASIS/basis.cm is stable]
[autoloading done]
3628800val it = () : unit

From Suppress "val it" output in Standard ML, How to disable SMLNJ warnings?, and SMLNJ want to remove "val it = () : unit" from every print statement execution, I got some hints how to suppress them.

I execute CM_VERBOSE=false sml < $filename and added one line of Control.Print.out := {say=fn _=>(), flush=fn()=>()}; in the code, but I still have some message:

Standard ML of New Jersey v110.77 [built: Tue Mar 10 07:03:24 2015]
- 3628800

How can I print out only the output?

Answer 1

The sml command is intended to be used interactively. It sounds to me like you would be better off building a standalone executable from your program instead.

There are a few options:

1. If you are relying on SML/NJ extensions, or if you simply cannot use another ML implementation, you can follow the instructions in this post to build an SML/NJ heap image that can be turned into a standalone executable using heap2exec.

2. A better option might be to use the MLton compiler, another implementation of Standard ML. It lacks a REPL, but unlike SML/NJ it requires no boilerplate to generate a standalone executable. Building is as simple as issuing:

   $ mlton your-program.sml
   $ ./your-program
   3628800