How do i use Xcode to run Fortran?

The core of Xcode is Apple's LLVM compiler, which, as I understand it, supports only C, Objective-C, Swift, and C++. And since Xcode is the only supported IDE for Apple's platforms, you need to pick one of those languages to use.

However, if you're just wanting to learn or teach Fortran or something like that, perhaps you can find a third-party compiler?

If you have a Fortran compiler installed on your system, you can create a build step that can call the compiler or run a Makefile to build the code.

short and quick solution

install homebrew

install gcc with gfortran

link to fortran libs in xcode

otherwise get a good fortran compiler like Portland and just link to the framework