Custom postgresql types


I have a question regarding postgresql and custom types defined in postgresql. I have a table, full_documents, with a column status, whose type is a custom enum type, named document_status_type.

When i try to run the following query

let query dbh= [%pgsql dbh "select status from full_documents limit 1000" ]

I have the following error:

Error: Unbound value document_status_type_of_string

I then define the function document_status_type_of_string as follow:

let document_status_type_of_string s= s

It then works, but I have the following warning:
Warning 33: unused open PGOCaml.

Is there something I could do to avoid having that warning ?

You could remove the line open PGOCaml from the code.