It depends on hoe you are writing your compiler. If you are coding in a high level language, then writing an AST interpreter for a functional language is super

It depends on hoe you are writing your compiler. If you are coding in a high level language, then writing an AST interpreter for a functional language is super simple. You just need to mix first-class functions and an unsurprising expression evaluator and you end up with something really expressive. If you are targeting a lower level language like assembly language then I think an imperative language is easier to do though. You need to worry a lot about memory layouts, register allocation and calling conventions and in this paradigm a simple imperative language will be an easier fit.