How about something like:

  let exists_in_complex_datastructure =
    let module M =
      struct
        exception Exit
        let eicd predicate complex_data_structure =
          try 
            map_for_effect_on_complex_data_structure
              (fun element -> if predicate element then raise Exit)
              complex_data_structure;
            false
          with Exit -> true
       end
     in M.eicd

That is, in the scope of your module (or within the function), create
a new exception for your use.  Since it's local to your function,
nobody else will be raising it.

John.
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