# Fac build system

Fac is a general-purpose build system inspired by make that utilizes ptrace to ensure that all dependences are enumerated and that all source files are added to a (git) repo. An important feature of fac is that it automatically handles dependencies, rather than either complaining about them or giving an incorrect build. Currently, fac only runs on linux systems, but on those systems it is incredibly easy to use!

• Automatically tracks build dependencies in a way that is independent of programming language. You are only required to specify the minimum of dependencies for each rule (which is often an empty set), and fac works out the rest for you. If you fail to specify dependencies, fac should still build successfully if you use it repeatedly.

• Parallel building.

• You are forced to write your configuration in a language of your own choice. (Or conversely, you are not forced to use a language of my choice, much less a custom-built language that I developed.)

• Integrates with git, to keep you from forgetting to git add a file that is needed for the build.

## How does it work?

• Fac uses ptrace to track every system call your build command makes. Thus we can see precisely which files are read, and which files are modified.

• Fac has an extremely simple declarative file format. There are no variables, no functions, no macros. Just data. This could be a problem for larger projects if you were forced to write these files by hand. But in most large projects you will just write a script to generate these files.

• You write your "build" script as a program (in the language of your choice) that creates a .fac file. This script is run (and re-run) using the same dependency-tracking mechanism that is used to for an ordinary build. Thus, you can get away with writing a simple but inefficient script, since it will only seldom be run. (Unlike, e.g. scons which has to rerun your SConstruct python file on every build.)

• If your build rules depend on the operating system, or the system environment, your "configure" script is the same program (in the language of your choice) that creates a .fac file. Or perhaps it provides input to the script that actually creates the .fac file.

For a lengthier introduction and motivation for fac, see Introducing fac.