[Haskell-cafe] dependent types

[Andrew U. Frank]

in modeling real application we have often the case that the type of
some object depends on a value. e.g. small_boat is a vessel with size
less than a constant. big_boat is a vessel with a larger size. for
example, many legal classifications are expressed in this form (e.g. car
vs. truck)
depending on the type, operations are applicable or not (e.g. road with
restriction 'no trucks'). 
how could one model such situations in haskell? i assume there are
several possibilities...