[Caml-list] How is this type inferred?

[Malcolm Matalka <mmatalka@gmail.com>]

I wrote a typed SQL interface where the usage is something like:

let sql = TS.(sql / "SELECT foo FROM bar WHERE x =" /% Var.int /^ "AND"
/% Var.string)

And then one can gets a value back of type:

(int -> string -> '_weak4, '_weak4) Sqlite_io.Typed_sql.t

And the type of all of that is:

  type ('f, 'r) t

  val sql : ('r, 'r) t

  val (/^) : ('f, 'r) t -> string -> ('f, 'r) t
  val (/%) : ('f, 'a -> 'r) t -> 'a Var.t -> ('f, 'r)  t

My question is:

How is the type of 'f inferred in there?  I managed to get this working
by cobbling together a bunch of things I didn't quite understand and now
I'm trying to figure it out.

Thanks,
/Malcolm