The MacPorts Project is an open-source community initiative to design an easy-to-use system for compiling, installing, and upgrading either command-line, X11 or Aqua based open-source software on the Mac OS X operating system.
The following GNAT related Ports are provided:
Apart from lang/gnat-gcc can be installed simple with the port command. i.E.:
sudo port install gnat-booch95
lang/gnat-gcc however needs a working Ada compiler to bootstrap. You can use the MacAda or a precompiled MacPort compiler. Depending on which compiler you choose you need to used the correct variant. For MacAda the variant is
+macada for MacPort the variant is
sudo port install gnat-gcc +macada