I like to see a complex build system as a data flow setup where the configuration is the input and the build artifacts are the output. Meson supports that model

I like to see a complex build system as a data flow setup where the configuration is the input and the build artifacts are the output. Meson supports that model nicely, and it hides (mostly) what happens at configuration time from what happens at build time. Future versions of Meson could move bits from Meson-time to ninja-time transparently. This, plus the fact that there is no aliasing (objects are either immutable or copied on assignment), means the imperative nature is mostly hidden. Heavily macroized Makefiles can have much more of an imperative style than meson.build files.