Make itself is largely a functional/declarative language. Beside the recipes (which aren't Make but actually shell, though you can use Haskell if you want), the only non-functional feature I can think of are the global variables, which most makefiles generally don't modify in a non-lexical manner anyway.
I was talking about tool like rake in ruby and scons in python. they are not declarative at all. But most important is that if what your are building needs you to set env variable ect... I don t see how it could really be done in a functionnal way(without side effects).
