a tiny ninja build generator

Stream: lean4

[Christian Pehle]

I've written a tiny ninja build file generator for lean4: https://github.com/cpehle/bl. It is meant to serve as a component in supporting lean4 compilation in Bazel. It also possible to use it standalone if you are keen on managing dependencies on your own :grinning: and don't like make (ninja compiles Lake ~8 faster than leanmake on my machine).