On 02/10/2015 04:06 PM, Gabriel Riba wrote:
Since [a] is no more in EqSet, I have to pair the Item structure and the Set
one when as input to the MkSetOps functor:
The solution is again a standard ML idiom.
signature SET = sig
type item
type t
val empty: t
val singleton : item -> t
val insert: item -> t -> t
val member: item -> t -> bool
val foldr: b ::: Type -> (item -> b -> b) -> b -> t -> b
end
functor EqSet(Q: sig type item
val eq_item: eq item
end): SET where type item = Q.item = struct ... end
(* *** code: *)
functor EqSet(Q: sig con item :: Type
val eq_item: eq item
end): sig
con t :: Type
val empty: t
val singleton : Q.item -> t
val insert: Q.item -> t -> t
val member: Q.item -> t -> bool
val foldr: b ::: Type -> (Q.item -> b -> b) -> b -> t -> b
end = struct
type t = list Q.item
val empty: t = []
val singleton (x: Q.item): t = x :: []
val member (x: Q.item) (li: t) = List.exists (eq x) li
val insert (x: Q.item) (xs : t) =
if member x xs then xs else x :: xs
val foldr [b]: (Q.item -> b -> b) -> b -> t -> b = List.foldr
end
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