Well, you could use arrays of optional bytes, but are use sure it's clever?

Maybe it's much better to define an abstract module of type

    module type Mem = sig
      type t
      val get_byte : t -> ~offset:int -> char option  
    end

And invent some clever (maybe lazy) implementation using just Bigarray?

BAP also has something like this in

https://github.com/BinaryAnalysisPlatform/bap/blob/master/li...

You could ask about BAP in general on

https://discuss.ocaml.org/

especially

https://discuss.ocaml.org/u/ivg/summary

(one of the guys behind BAP, very clever and talented in explaining stuff)