5.3.7 [2022.01.09]
* Relax the Bind constraints in the following instances to Functor:
-instance (Bind f, Monad f) => Alt (MaybeT f)
-instance (Bind f, Monad f) => Plus (MaybeT f)
+instance (Functor f, Monad f) => Alt (MaybeT f)
+instance (Functor f, Monad f) => Plus (MaybeT f)
-instance (Bind f, Monad f, Semigroup e) => Alt (ExceptT e f)
-instance (Bind f, Monad f, Semigroup e, Monoid e) => Plus (ExceptT e f)
+instance (Functor f, Monad f, Semigroup e) => Alt (ExceptT e f)
+instance (Functor f, Monad f, Semigroup e, Monoid e) => Plus (ExceptT e f)
-- If building with transformers-0.5.* or older
-instance (Bind f, Monad f) => Alt (ErrorT e f)
-instance (Bind f, Monad f, Error e) => Plus (ErrorT e f
+instance (Functor f, Monad f) => Alt (ErrorT e f)
+instance (Functor f, Monad f, Error e) => Plus (ErrorT e f)
5.3.6 [2021.10.07]
* Allow building with GHC 9.2.
* Allow building with transformers-0.6.*.
* Add Alt instance for Identity.
* Add Conclude, Decide and Divise type classes and instances.
* Add (<.*>), (<*.>), and traverseMaybe functions, which make it easier to
defined Traversable1 instances for data types that have fields with a
combination of Traversable and Traversable1 instances.
* Add Semigroupoids.Do module with overloads for use with QualifiedDo.
* Add Apply, Alt, Plus, Bind and BindTrans instances for the CPS versions
of WriterT and RWST.
* Add psum function to Data.Functor.Plus.
* Add Categorical data type.
* The build-type has been changed from Custom to Simple. To achieve
this, the doctests test suite has been removed in favor of using
cabal-docspec to run the doctests.
* Explicitly mark modules as Safe.
Provides a wide array of (semi)groupoids and operations for working with them.
A Semigroupoid is a Category without the requirement of identity arrows
for every object in the category.
A Category is any Semigroupoid for which the Yoneda lemma holds.
When working with comonads you often have the <*> portion of an Applicative,
but not the pure. This was captured in Uustalu and Vene's
"Essence of Dataflow Programming" in the form of the ComonadZip class
in the days before Applicative. Apply provides a weaker invariant,
but for the comonads used for data flow programming
(found in the streams package), this invariant is preserved.
Applicative function composition forms a semigroupoid.
Similarly many structures are nearly a comonad, but not quite,
for instance lists provide a reasonable extend operation in the form of tails,
but do not always contain a value.
