In case you're interested in more sophisticated examples of the DSL +
phantom types combination, I've worked on [Macaque] wich is a SQL DSL
for Caml using essentially the same technique. We were able to encode
useful properties of the SQL values, such as nullability, in the OCaml
type system.
The translation from the DSL to the caml code is not always direct,
because in some case you want to generate elaborate source terms wich
use the type system to enforce static guarantees (eg. correcteness of
the GROUP BY clauses).

 [Macaque] http://macaque.forge.ocamlcore.org/