This is an application written using literate Haskell.
This means that the Haskell source files have extension .lhs
and are LaTeX sources with Haskell embedded in
\begin{code}..\end{code} environments.
The main file for the application program is src/UTP2.lhs
The main file for the enclosing LaTeX documentation is UTP2-MAIN.tex
A Hackers Guide is being prepared in UTP2-Hacking-MAIN.tex
The following instructions have shown to build UTP2 on macOS 10.11.6 on a relatively fresh install.
UTP2 requires the command-line tool wx-config which can be installed as part
of wx. With Homebrew this is as easy as: brew install wxmac
XCode developer tools are also required, however they can't just be installed
via xcode-select --install since they are searched for in very specific
locations, maybe you can symlink them? Instead install XCode from the App
Store. You might have to agree to XCode's terms and conditions which you can
find by opening XCode.
The project should now build with stack.