I know how to type the arguments, and I like to do it, since I will get the
compile errors directly, not first when I use the function.

Thus, I typical write a function like

(* return the column called name *)
let find (columns:columns) (name:column_type) =
  List.find ( fun column -> column.data_type = name ) columns.columns

which has typing

val find : columns -> column_type -> column = <fun>

If I use the interactive environment, I see that I get the expected result
column. I needed to see this, since this is my first use of List.find, and I
wanted to be sure that it returned the column.

However, I would have liked to say this already in the definition of find,
that the result of my function find should be a column. How is this done?

/mattias

P.s. I like to type, since I think it is belongs to the documentation of the
code.

P.P.s. How to type arguments is not very well described in the
documentation. I found one example, twice.