OpenBSD ports of MLton and Ur/Web compilers
Binary packages for OpenBSD 5.9 amd64 are available in the release section of this repository - https://github.com/extensibl/ports/releases/.
Building your own set of packages for any other version of OpenBSD (amd64) is easy - download mlton/ and urweb/ into the lang/ directory of your local ports tree and run make install.
Refer to the OpenBSD ports guide for full, detailed instructions:
http://www.openbsd.org/faq/faq15.html#Ports