I think one build tool that has the fundamental abstraction well thought out is mill (written in Scala). Every task is just an ordinary function written in plai

I think one build tool that has the fundamental abstraction well thought out is mill (written in Scala). Every task is just an ordinary function written in plain Scala, outputting something. Other functions can use this output by simply calling that function. In many cases the output will be simply a target directory, that is cached when none of the dependencies have changed.