There's no such thing as "fully-imperative, zero-declarative language" -- at least not one as high level C# or Python -- because declarative/imperative are programming styles, which languages can make more natural but which are used with all (well, higher-level than assembly) languages.
Did I misunderstand what you mean?
For example, it is possible to embed backtracking logic programming [1] into Haskell with not a big effort.
Oh sorry. Did I let my schadenfreude out again?