CML using SML-NJ --- Error: unbound structure: Test in path Test.main

Question

I sucessfully compiled SML using the instructions from here and I try to execute this CML hello world program:

% cat cml_test.cm
Library
    structure Hello
is
    $cml/basis.cm
    $cml/cml.cm
    cml_test.sml

% cat cml_test.sml
structure Hello = struct
    open CML

    fun hello () = let
        val c : string chan = channel ()
        in
            spawn (fn () => TextIO.print (recv c));
            send (c, "Hello, world!\n");
            exit ()
        end

    fun main (_, argv) =
        RunCML.doit (fn () => ignore (spawn hello), NONE)
end

I tried to compile it like this:

% /work/smlnj/bin/ml-build /work/cml/cml_test.cm
Standard ML of New Jersey [Version 110.99.7.1; 64-bit; January 17, 2025]
[scanning /work/cml/cml_test.cm]
[library $cml/basis.cm is stable]
[library $cml/cml.cm is stable]
[library $cml/cml-internal.cm is stable]
[library $cml/core-cml.cm is stable]
[library $SMLNJ-BASIS/basis.cm is stable]
[library $SMLNJ-BASIS/(basis.cm):basis-common.cm is stable]
[loading /work/cml/(cml_test.cm):cml_test.sml]
[scanning 1756284-export.cm]
[scanning /work/cml/cml_test.cm]
[parsing (1756284-export.cm):1756284-export.sml]
[compiling (1756284-export.cm):1756284-export.sml]
1756284-export.sml:1.72-1.81 Error: unbound structure: Test in path Test.main
Compilation failed.

When I try to execute the print from REPL, it works:

% ./sml
Standard ML of New Jersey [Version 110.99.7.1; 64-bit; January 17, 2025]
- 1+2;
val it = 3 : int
- TextIO.print("hello\n");
[autoloading]
[library $SMLNJ-BASIS/basis.cm is stable]
[library $SMLNJ-BASIS/(basis.cm):basis-common.cm is stable]
[autoloading done]
hello
val it = () : unit
-

Any help, please ?

Sam Westrick · Accepted Answer · 2025-05-12 14:16:38Z

1

The issue is just that ml-build expects you to specify a main function. If you don't specify it, it defaults to Test.main, which is why you are seeing the error "unbound structure: Test in path Test.main"

For your program, we need to tell it that the main function is called Hello.main.

This incantation works:

$ ml-build cml_test.cm Hello.main
$ sml @SMLload=cml_test
Hello, world!

answered May 12 at 14:16

Sam Westrick

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