Diff two structures.

>>> :{
  let
    old = fromList [("Alice", 1), ("Bob", 2)]
    new = fromList [("Alice", 3), ("Carol", 4)]
  in
    diff old new :: Map String (Maybe Int)
:}
fromList [("Alice",Just 3),("Bob",Nothing),("Carol",Just 4)]

Since: 0.1.0.0

Diff two structures without requiring an Eq instance. Instead, always assume a new value wherever the structures align:

>>> :{
  let
    old = fromList [("Alice", (+ 1))]
    new = fromList [("Alice", (* 2))]
  in
    ($ 3) <$> diffNoEq old new ! "Alice"
:}
Just 6

Since: 0.1.0.0

Diff two structures with a custom function.

This function should return Nothing if there is no meaningful change and Just new to indicate a changed value.

Often, c is itself a Maybe, to indicate deletion/replacement of a value.

Since: 0.1.0.0

Apply a patch to a structure.

>>> patch (fromList [(0, Just 0), (1, Just 3), (2, Nothing)]) (fromList [(0, 1), (2, 3)])
fromList [(0,0),(1,3)]

When the types are compatible, patch undoes diff / diffNoEq:

\old new -> let p = diff @(Map Int (Maybe Int)) old (new :: Map Int Int) in (patch p old) == new

\old new -> let p = diffNoEq @(Map Int (Maybe Int)) old (new :: Map Int Int) in (patch p old) == new

Since: 0.1.0.0

Apply changes to a structure with a custom function, folding over the patch.

The provided function receives two arguments: the old value if present and the new value from the patch. It should return Just new to store new into the result, or Nothing to delete it.

Since: 0.1.0.0