Q:

string option to string conversion

How do I convert the string option data type to string in Ocaml? 
let function1 data = 
  match data with
   None -> ""
   | Some str -> str 

Is my implementation error free? Here 'data' has a value of type string option.

A:

To answer your question, yes.
For this simple function, you can easily find it in Option module. For example, Option.default totally fits your purpose:
let get_string data = 
    Option.default "" data

There are many other useful functions for working with option types in that module, you should check them out to avoid redefine unnecessary functions.

A:

Another point is that the compiler would tell you if there's something wrong.  If the compiler doesn't complain, you know that the types all make sense and that you have covered every case in your match expression.  The OCaml type system is exceptionally good at finding problems while staying out of your way.   Note that you haven't had to define any types yourself in this small example--the compiler will infer that the type of data is string option.
A lot of the problems the compiler can't detect are ones that we can't detect either.  We can't tell whether mapping None to the empty string is what you really wanted to do, though it seems very sensible.

