@@ -1,6 +1,6 @@
11module Data.SortedMap
22
3−-- TODO: write merge and split
3+-- TODO: write split
44
55private
66data Tree : Nat -> (k : Type) -> Type -> Ord k -> Type where
@@ -214,6 +214,9 @@ insert k v (M _ t) =
214214 Left t' => (M _ t')
215215 Right t' => (M _ t')
216216
217+insertFrom : Foldable f => f (k, v) -> SortedMap k v -> SortedMap k v
218+insertFrom = flip $ foldl $ flip $ uncurry insert
219+
217220export
218221delete : k -> SortedMap k v -> SortedMap k v
219222delete _ Empty = Empty
@@ -235,6 +238,16 @@ toList : SortedMap k v -> List (k, v)
235238toList Empty = []
236239toList (M _ t) = treeToList t
237240
241+||| Gets the keys of the map.
242+export
243+keys : SortedMap k v -> List k
244+keys = map fst . toList
245+
246+||| Gets the values of the map. Could contain duplicates.
247+export
248+values : SortedMap k v -> List v
249+values = map snd . toList
250+
238251treeMap : (a -> b) -> Tree n k a o -> Tree n k b o
239252treeMap f (Leaf k v) = Leaf k (f v)
240253treeMap f (Branch2 t1 k t2) = Branch2 (treeMap f t1) k (treeMap f t2)
@@ -245,3 +258,40 @@ export
245258implementation Functor (SortedMap k) where
246259 map _ Empty = Empty
247260 map f (M n t) = M _ (treeMap f t)
261+
262+||| Merge two maps. When encountering duplicate keys, using a function to combine the values.
263+||| Uses the ordering of the first map given.
264+export
265+mergeWith : (v -> v -> v) -> SortedMap k v -> SortedMap k v -> SortedMap k v
266+mergeWith f x y = insertFrom inserted x where
267+ inserted : List (k, v)
268+ inserted = do
269+ (k, v) <- toList y
270+ let v' = (maybe id f $ lookup k x) v
271+ pure (k, v')
272+
273+||| Merge two maps using the Semigroup (and by extension, Monoid) operation.
274+||| Uses mergeWith internally, so the ordering of the left map is kept.
275+export
276+merge : Semigroup v => SortedMap k v -> SortedMap k v -> SortedMap k v
277+merge = mergeWith (<+>)
278+
279+||| Left-biased merge, also keeps the ordering specified by the left map.
280+export
281+mergeLeft : SortedMap k v -> SortedMap k v -> SortedMap k v
282+mergeLeft = mergeWith const
283+
284+-- TODO: is this the right variant of merge to use for this? I think it is, but
285+-- I could also see the advantages of using `mergeLeft`. The current approach is
286+-- strictly more powerful I believe, because `mergeLeft` can be emulated with
287+-- the `First` monoid. However, this does require more code to do the same
288+-- thing.
289+export
290+Semigroup v => Semigroup (SortedMap k v) where
291+ (<+>) = merge
292+
293+||| For `neutral <+> y`, y is rebuilt in `Ord k`, so this is not a "strict" Monoid.
294+||| However, semantically, it should be equal.
295+export
296+(Ord k, Semigroup v) => Monoid (SortedMap k v) where
297+ neutral = empty