These instructions are for installing Standard ML of New Jersey (SML/NJ) on macOS.

Using the installer package

The most direct way to install SML/NJ is to use one of the provided installer packages:

These packages put the installation in /usr/local/smlnj. If there is an existing installation, then it will be updated. We recommend that you add /usr/local/smlnj/bin to your shell’s PATH variable.

There is also a Homebrew cask that wraps the 64-bit installation package. If you have homebrew installed, then you can run the following command to install SML/NJ:

% brew cask install smlnj

If you have previously installed SML/NJ using Homebrew, then you will need to use the command

% brew cask upgrade smlnj

Installing from source

It is also possible to install SML/NJ from source code and the pre-compiled bin files. To do so, you will need a copy of Apple’s Xcode development environment. Furthermore, you will need to install the command-line tools, which you can do by running the command

% xcode-select --install

With the command-line tools installed, you can follow the standard instructions for installing on Unix/Linux systems.


For macOS 10.13 High Sierra and earlier, the default install is 32-bits. Starting with macOS 10.14 Mojave, the default install is 64 bits. It is possible to install SML/NJ on Mojave, but it requires some extra steps (see the instructions below).

Installing 32-bit SML/NJ on macOS 10.14 (Mojave)

Xcode 10.1 (and later) does not include the libraries needed to build 32-bit executables, such as the SML/NJ runtime.

To support building on Mojave, there is a special makefile (mk.x86-darwin18) for the runtime system and the config/ uses this makefile when necessary. This makefile expects that the MacOSX10.13.sdk directory from Xcode 9 has been copied into the Xcode 10 SDKs directory. Note that updating Xcode from the AppStore will remove the 10.13 SDK, so you should keep a copy in a safe place.

The Xcode SDKs live in Platforms/MacOSX.platform/Developer/SDKs under the Developer directory. One can determine the path to the current developer directory using the command

% xcode-select -p

Quarantine issues

Another issue that you may encounter when building from source on macOs 10.14 Mojave is an error message for a shell script of the form

  /bin/sh: bad interpreter: Operation not permitted

This error arises because the shell script has the attribute set. To fix the problem, remove the attribute using the command

% xattr -d shell-script

and resume the build.