diff --git a/CHANGELOG.md b/CHANGELOG.md --- a/CHANGELOG.md +++ b/CHANGELOG.md @@ -5,10 +5,46 @@ The format is based on [Keep a Changelog 1.1](https://keepachangelog.com/en/1.1.0/), and this project adheres to the [Haskell Package Versioning Policy](https://pvp.haskell.org/). -## [0.0.1.0] - +## [0.1.0.0] - 2026-08-04 ### Added +- `Applicative` and `Monad` instances for `Commutative` itself, so it can be + used with `DerivingVia` to give your own commutative `Monad` a `Duoidal` + instance, rather than only being usable through `Parallel` and `Sequential` +- `commutativeAp` and `sequentialAp` +- `Normal` duoidal instances for the commutative functors in base: `Complex`, + `Down`, `Dual`, `Identity`, `Max`, `Maybe`, `Min`, `Monoid.First`, + `Monoid.Last`, `Monoid.Product`, `Proxy`, `Semigroup.First`, `Semigroup.Last`, + `Solo`, `Sum`, `->`, `(,,)`, `(,,,)`, and `Const` +- Cabal flag `lint`, which (when disabled, as is the default) allows the + dependency graph to be pruned, potentially avoiding solver & compilation + issues. + +### Changed + +- `Applicative (Parallel (Commutative f))` and `Applicative (Sequential + (Commutative f))` now require `f` to be a `Monad` rather than merely an + `Applicative`. `Commutative` was always documented as being for commutative + `Monad`s, but the instances asked for less than they meant; the new + `Commutative` instances need the stronger constraint. + +### Deprecated + +- `sequentialLiftA2` — use `sequentialAp` instead + +### Fixed + +- `no-recursion` is no longer a dependency by default (thanks to the + aforementioned `lint` change). + +## [0.0.1.0] - 2025-11-17 + +### Added + - initial release of this package -[0.0.1.0]: https://github.com/sellout/duoids/releases/tag/v0.0.1.0 + + +[0.1.0.0]: https://github.com/sellout/duoids/compare/v0.1.0...v1.0.0 +[0.0.1.0]: https://github.com/sellout/duoids/releases/tag/v0.1.0 diff --git a/README.md b/README.md --- a/README.md +++ b/README.md @@ -107,11 +107,15 @@ ### [either](https://hackage.haskell.org/package/either) -The `either` package has a `Validation` type that’s isomorphic to `Either` and has an applicative instance that’s the same as the `Parallel (Either e)` instance here. However, it doesn’t have anything like the `Duoidal` class, and so requires manual conversion back and forth between `Either` and `Validation`. +The `either` package has a `Validation` type that’s isomorphic to `Either` and has an `Applicative` instance that’s the same as the `Parallel (Either e)` instance here. However, it doesn’t have anything like the `Duoidal` class, and so requires manual conversion back and forth between `Either` and `Validation`. ### [Haskerwaul](https://github.com/sellout/haskerwaul#readme) A broader package that contains a more general (category polymorphic) implementation of duoids. It’s also much less pragmatic. + +### [multi-except](https://hackage.haskell.org/package/multi-except) + +This seems like another approach to `Validation`, but I haven’t used it. ### [United Monoids](https://github.com/snowleopard/united) diff --git a/Setup.hs b/Setup.hs --- a/Setup.hs +++ b/Setup.hs @@ -7,7 +7,6 @@ -- Warns even when `Unsafe` is explicit, not inferred. See -- https://gitlab.haskell.org/ghc/ghc/-/issues/16689 {-# OPTIONS_GHC -Wno-unsafe #-} -{-# OPTIONS_GHC -fplugin=NoRecursion #-} module Main (main) where diff --git a/docs/license-report.md b/docs/license-report.md --- a/docs/license-report.md +++ b/docs/license-report.md @@ -9,7 +9,7 @@ | Name | Version | [SPDX](https://spdx.org/licenses/) License Id | Description | Also depended upon by | | --- | --- | --- | --- | --- | | **`base`** | [`4.20.0.0`](http://hackage.haskell.org/package/base-4.20.0.0) | [`BSD-3-Clause`](http://hackage.haskell.org/package/base-4.20.0.0/src/LICENSE) | Core data structures and operations | *(core library)* | -| `no-recursion` | [`0.3.0.0`](http://hackage.haskell.org/package/no-recursion-0.3.0.0) | [`(AGPL-3.0-only WITH Universal-FOSS-exception-1.0 OR AGPL-3.0-only OR LicenseRef-commercial)`](http://hackage.haskell.org/package/no-recursion-0.3.0.0/src/LICENSE) | A GHC plugin to remove support for recursion | | +| `no-recursion` | [`0.4.0.1`](http://hackage.haskell.org/package/no-recursion-0.4.0.1) | [`(AGPL-3.0-only WITH Universal-FOSS-exception-1.0 OR LicenseRef-proprietary)`](http://hackage.haskell.org/package/no-recursion-0.4.0.1/src/LICENSE) | A GHC plugin to remove support for recursion | | ## Indirect transitive dependencies @@ -23,10 +23,11 @@ | **`directory`** | [`1.3.8.3`](http://hackage.haskell.org/package/directory-1.3.8.3) | [`BSD-3-Clause`](http://hackage.haskell.org/package/directory-1.3.8.3/src/LICENSE) | Platform-agnostic library for filesystem operations | `ghc`, `ghc-boot`, `hpc`, `process` | | **`exceptions`** | [`0.10.7`](http://hackage.haskell.org/package/exceptions-0.10.7) | [`BSD-3-Clause`](http://hackage.haskell.org/package/exceptions-0.10.7/src/LICENSE) | Extensible optionally-pure exceptions | `filepath`, `ghc`, `os-string`, `semaphore-compat` | | **`filepath`** | [`1.5.2.0`](http://hackage.haskell.org/package/filepath-1.5.2.0) | [`BSD-3-Clause`](http://hackage.haskell.org/package/filepath-1.5.2.0/src/LICENSE) | Library for manipulating FilePaths in a cross platform way. | `directory`, `ghc`, `ghc-boot`, `ghci`, `hpc`, `process`, `unix` | -| **`ghc`** | [`9.10.1`](http://hackage.haskell.org/package/ghc-9.10.1) | [`BSD-3-Clause`](http://hackage.haskell.org/package/ghc-9.10.1/src/LICENSE) | The GHC API | `no-recursion` | +| **`ghc`** | [`9.10.1`](http://hackage.haskell.org/package/ghc-9.10.1) | [`BSD-3-Clause`](http://hackage.haskell.org/package/ghc-9.10.1/src/LICENSE) | The GHC API | `ghc-compat-plugin`, `no-recursion` | | **`ghc-bignum`** | [`1.3`](http://hackage.haskell.org/package/ghc-bignum-1.3) | [`BSD-3-Clause`](http://hackage.haskell.org/package/ghc-bignum-1.3/src/LICENSE) | GHC BigNum library | `ghc-internal` | | **`ghc-boot`** | [`9.10.1`](http://hackage.haskell.org/package/ghc-boot-9.10.1) | [`BSD-3-Clause`](http://hackage.haskell.org/package/ghc-boot-9.10.1/src/LICENSE) | Shared functionality between GHC and its boot libraries | `ghc`, `ghci` | -| **`ghc-boot-th`** | [`9.10.1`](http://hackage.haskell.org/package/ghc-boot-th-9.10.1) | [`BSD-3-Clause`](http://hackage.haskell.org/package/ghc-boot-th-9.10.1/src/LICENSE) | Shared functionality between GHC and the @template-haskell@ library | `ghc-boot`, `template-haskell` | +| **`ghc-boot-th`** | [`9.10.1`](http://hackage.haskell.org/package/ghc-boot-th-9.10.1) | [`BSD-3-Clause`](http://hackage.haskell.org/package/ghc-boot-th-9.10.1/src/LICENSE) | Shared functionality between GHC and the @template-haskell@ library | `ghc-boot`, `ghc-compat-plugin`, `template-haskell` | +| `ghc-compat-plugin` | [`0.1.0.1`](http://hackage.haskell.org/package/ghc-compat-plugin-0.1.0.1) | [`AGPL-3.0-only`](http://hackage.haskell.org/package/ghc-compat-plugin-0.1.0.1/src/LICENSE.AGPL-3.0-only) | Eases support for multiple GHC versions | `no-recursion` | | **`ghc-heap`** | [`9.10.1`](http://hackage.haskell.org/package/ghc-heap-9.10.1) | [`BSD-3-Clause`](http://hackage.haskell.org/package/ghc-heap-9.10.1/src/LICENSE) | Functions for walking GHC's heap | `ghc`, `ghci` | | **`ghc-internal`** | [`9.1001.0`](http://hackage.haskell.org/package/ghc-internal-9.1001.0) | [`BSD-3-Clause`](http://hackage.haskell.org/package/ghc-internal-9.1001.0/src/LICENSE) | Basic libraries | `base`, `ghc-heap` | | **`ghc-platform`** | [`0.1.0.0`](http://hackage.haskell.org/package/ghc-platform-0.1.0.0) | *MISSING* | *MISSING* | `ghc-boot` | diff --git a/duoids.cabal b/duoids.cabal --- a/duoids.cabal +++ b/duoids.cabal @@ -1,7 +1,7 @@ cabal-version: 3.0 name: duoids -version: 0.0.1.0 +version: 0.1.0.0 synopsis: Unifying parallel and sequential operations description: Duoids relate a pair of monoids, where one can be seen as “parallel” and the other “sequential”. @@ -38,17 +38,6 @@ location: https://github.com/sellout/duoids.git subdir: core -flag noisy-deprecations - description: - Prior to GHC 9.10, the @DEPRECATED@ pragma can’t distinguish between terms - and types. Consenquently, you can get spurious warnings when there’s a name - collision and the name in the other namespace is deprecated. Or you can - choose to not get those warnings, at the risk of not being warned when - there’s a name collision and the namespace you’re referencing is the one - that’s deprecated. - default: True - manual: False - custom-setup setup-depends: -- TODO: Due to haskell/cabal#3751, `Cabal` has to be specified even though @@ -59,8 +48,27 @@ Cabal >= 3.0 && < 99, base ^>= {4.18.0, 4.19.0, 4.20.0, 4.21.0}, cabal-doctest ^>= {1.0.0}, - no-recursion ^>= {0.2.0, 0.3.0}, +flag noisy-deprecations + description: + Prior to GHC 9.10, the @DEPRECATED@ pragma can’t distinguish between terms + and types. Consenquently, you can get spurious warnings when there’s a name + collision and the name in the other namespace is deprecated. Or you can + choose to not get those warnings, at the risk of not being warned when + there’s a name collision and the namespace you’re referencing is the one + that’s deprecated. + default: True + -- Because disabling this flag won’t help the solver. + manual: True + +flag lint + description: + Compile with "NoRecursion" enabled. This is intended for developers of this + package. + default: False + -- Because disabling this flag won’t help the solver. + manual: True + -- This mimics the GHC2024 extension -- (https://ghc.gitlab.haskell.org/ghc/doc/users_guide/exts/control.html?highlight=doandifthenelse#extension-GHC2024), -- but supporting compilers back to GHC 8.0. If the oldest supported compiler @@ -84,7 +92,6 @@ import: GHC2024 build-depends: base ^>= {4.18.0, 4.19.0, 4.20.0, 4.21.0}, - no-recursion ^>= {0.2.0, 0.3.0}, ghc-options: -Weverything -- This one just reports unfixable things, AFAICT. @@ -94,7 +101,6 @@ -- Warns even when `Unsafe` is explicit, not inferred. See -- https://gitlab.haskell.org/ghc/ghc/-/issues/16689 -Wno-unsafe - -fplugin=NoRecursion if impl(ghc >= 9.8.1) ghc-options: -- Inference good. @@ -121,11 +127,18 @@ NoStarIsType NoTypeApplications if flag(noisy-deprecations) - cpp-options: -DSELLOUT_NOISY_DEPRECATIONS + cpp-options: + -DSELLOUT_NOISY_DEPRECATIONS + if flag(lint) + build-depends: + no-recursion ^>= {0.2.0, 0.3.0, 0.4.0}, + ghc-options: + -fplugin=NoRecursion library import: defaults - hs-source-dirs: src + hs-source-dirs: + src exposed-modules: Control.Duoidal Control.Duoidal.Either @@ -141,7 +154,7 @@ hs-source-dirs: tests main-is: doctests.hs build-depends: - doctest ^>= {0.21.1, 0.22.6, 0.24.0}, + doctest ^>= {0.21.1, 0.22.6, 0.24.0, 0.25.0}, duoids, -- TODO: The sections below here are necessary because we don’t have control -- over the generated `Build_doctests.hs` file. So we have to silence diff --git a/src/Control/Duoidal.hs b/src/Control/Duoidal.hs --- a/src/Control/Duoidal.hs +++ b/src/Control/Duoidal.hs @@ -141,16 +141,24 @@ -- * instance helpers normalPure, + sequentialAp, sequentialBind, sequentialLiftA2, sequentialPure, -- * duoids from commutative `Monad`s Commutative (Commutative, getCommutative), + commutativeAp, ) where -import "base" Control.Applicative (Alternative, Applicative, empty, (<|>)) +import "base" Control.Applicative + ( Alternative, + Applicative, + Const (Const), + empty, + (<|>), + ) import "base" Control.Applicative qualified as Base ( liftA2, liftA3, @@ -163,7 +171,8 @@ import "base" Control.Category ((.)) import "base" Control.Monad (Monad) import "base" Control.Monad qualified as Base - ( forever, + ( ap, + forever, join, liftM2, return, @@ -182,18 +191,25 @@ bitraverse, ) import "base" Data.Bool (Bool) +import "base" Data.Complex (Complex) import "base" Data.Either (Either (Left, Right), either) import "base" Data.Eq (Eq) import "base" Data.Foldable (Foldable) import "base" Data.Foldable qualified as Base (for_, traverse_) import "base" Data.Function (const, ($)) import "base" Data.Functor (Functor, fmap) +import "base" Data.Functor.Identity (Identity) import "base" Data.Kind (Constraint, Type) -import "base" Data.Monoid (Monoid, mempty) -import "base" Data.Ord (Ord) -import "base" Data.Semigroup (Semigroup, (<>)) +import "base" Data.Maybe (Maybe) +import "base" Data.Monoid (Dual, Monoid, Sum, mempty) +import "base" Data.Monoid qualified as Monoid +import "base" Data.Ord (Down, Ord) +import "base" Data.Proxy (Proxy) +import "base" Data.Semigroup (Max, Min, Semigroup, (<>)) +import "base" Data.Semigroup qualified as Semigroup import "base" Data.Traversable (Traversable) import "base" Data.Traversable qualified as Base (for, traverse) +import "base" Data.Tuple (Solo) import "base" GHC.TypeError (ErrorMessage (Text), TypeError) import "base" System.IO (IO) import "base" Text.Read (Read) @@ -467,7 +483,12 @@ Sequential f b -> Sequential f c sequentialLiftA2 f (Sequential a) = Sequential . Base.liftA2 f a . getSequential +{-# DEPRECATED sequentialLiftA2 "use ‘sequentialAp’ instead" #-} +sequentialAp :: + (Monad f) => Sequential f (a -> b) -> Sequential f a -> Sequential f b +sequentialAp (Sequential f) = Sequential . Base.ap f . getSequential + sequentialBind :: (Monad f) => Sequential f a -> (a -> Sequential f b) -> Sequential f b sequentialBind (Sequential a) f = Sequential $ a Base.>>= (getSequential . f) @@ -476,25 +497,329 @@ -- | Commutative `Monad`s form a duoid with themselves. -- --- __NB__: Don’t use this newtype on a non-commutative Monad. +-- You can use this with @DerivingVia@ to create instances for your own +-- commutative `Monad`s. +-- +-- For existing types, instances for types in base should be available here, +-- but those for other packages may not exist. For those that don’t, you can +-- +-- 1. wrap the type in `Commutative` when you need the instance, +-- 2. define orphan instances that look like the instances for `Commutative`, or +-- 3. use the provided operations (like `commutativeAp`) directly. +-- +-- Some examples of commutative monads: +-- - those isomorphic to `Identity` (many newtypes fall into this bucket) +-- - reader (@->@) +-- - `Maybe` +-- - `Proxy` +-- +-- You can also wrap types that already have `Duoidal` instances in +-- `Commutative` as well (as long as they have an unwrapped `Monad` instance). +-- If their existing `Duoidal` instance isn’t the commutative one, the +-- `Commutative` wrapper will give you the commutative one. I don’t know if +-- this one is correct, but if you have a commutative writer (say, @`Writer` +-- (`Set` `Char`)@), wrapping it in `Commutative` would give you a `Duoidal` +-- instance that behaves commutatively. However, @`Set` a@ should already have +-- a commutative `Duoid` instance, so I don’t think it actually buys you +-- anything. +-- +-- __NB__: Don’t use this newtype to turn a non-commutative `Monad` into a +-- duoid. type Commutative :: forall {k}. (k -> Type) -> k -> Type newtype Commutative f a = Commutative {getCommutative :: f a} deriving stock (Eq, Ord, Read, Show, Functor, Foldable, Traversable) -instance (Applicative f) => Applicative (Parallel (Commutative f)) where - pure = Parallel . Commutative . Base.pure - liftA2 f (Parallel (Commutative a)) (Parallel (Commutative b)) = - Parallel . Commutative $ Base.liftA2 f a b +instance (Monad f) => Applicative (Commutative f) where + pure = Commutative . Base.return + Commutative f <*> Commutative a = Commutative $ Base.ap f a -instance (Applicative f) => Applicative (Sequential (Commutative f)) where - pure = Sequential . Commutative . Base.pure - liftA2 f (Sequential (Commutative a)) (Sequential (Commutative b)) = - Sequential . Commutative $ Base.liftA2 f a b +instance (Monad f) => Monad (Commutative f) where + Commutative a >>= f = Commutative $ a Base.>>= (getCommutative . f) +commutativeAp :: + (Monad f) => + Parallel f (a -> b) -> + Parallel f a -> + Parallel f b +commutativeAp (Parallel f) = Parallel . Base.ap f . getParallel + +instance (Monad f) => Applicative (Parallel (Commutative f)) where + pure = normalPure + (<*>) = commutativeAp + +instance (Monad f) => Applicative (Sequential (Commutative f)) where + pure = sequentialPure + (<*>) = sequentialAp + instance (Monad f) => Monad (Sequential (Commutative f)) where - Sequential (Commutative a) >>= f = - Sequential . Commutative $ a Base.>>= (getCommutative . getSequential . f) + (>>=) = sequentialBind +instance (Monad f) => Normal (Commutative f) + +-- `Complex` is a commutative duoidal functor + +instance Applicative (Parallel Complex) where + pure = normalPure + (<*>) = commutativeAp + +instance Applicative (Sequential Complex) where + pure = sequentialPure + (<*>) = sequentialAp + +instance Monad (Sequential Complex) where + (>>=) = sequentialBind + +instance Normal Complex + +-- `Down` is a commutative duoidal functor + +instance Applicative (Parallel Down) where + pure = normalPure + (<*>) = commutativeAp + +instance Applicative (Sequential Down) where + pure = sequentialPure + (<*>) = sequentialAp + +instance Monad (Sequential Down) where + (>>=) = sequentialBind + +instance Normal Down + +-- `Dual` is a commutative duoidal functor + +instance Applicative (Parallel Dual) where + pure = normalPure + (<*>) = commutativeAp + +instance Applicative (Sequential Dual) where + pure = sequentialPure + (<*>) = sequentialAp + +instance Monad (Sequential Dual) where + (>>=) = sequentialBind + +instance Normal Dual + +-- `Monoid.First` is a commutative duoidal functor + +instance Applicative (Parallel Monoid.First) where + pure = normalPure + (<*>) = commutativeAp + +instance Applicative (Sequential Monoid.First) where + pure = sequentialPure + (<*>) = sequentialAp + +instance Monad (Sequential Monoid.First) where + (>>=) = sequentialBind + +instance Normal Monoid.First + +-- `Semigroup.First` is a commutative duoidal functor + +instance Applicative (Parallel Semigroup.First) where + pure = normalPure + (<*>) = commutativeAp + +instance Applicative (Sequential Semigroup.First) where + pure = sequentialPure + (<*>) = sequentialAp + +instance Monad (Sequential Semigroup.First) where + (>>=) = sequentialBind + +instance Normal Semigroup.First + +-- `Identity` is a commutative duoidal functor + +instance Applicative (Parallel Identity) where + pure = normalPure + (<*>) = commutativeAp + +instance Applicative (Sequential Identity) where + pure = sequentialPure + (<*>) = sequentialAp + +instance Monad (Sequential Identity) where + (>>=) = sequentialBind + +instance Normal Identity + +-- `Monoid.Last` is a commutative duoidal functor + +instance Applicative (Parallel Monoid.Last) where + pure = normalPure + (<*>) = commutativeAp + +instance Applicative (Sequential Monoid.Last) where + pure = sequentialPure + (<*>) = sequentialAp + +instance Monad (Sequential Monoid.Last) where + (>>=) = sequentialBind + +instance Normal Monoid.Last + +-- `Semigroup.Last` is a commutative duoidal functor + +instance Applicative (Parallel Semigroup.Last) where + pure = normalPure + (<*>) = commutativeAp + +instance Applicative (Sequential Semigroup.Last) where + pure = sequentialPure + (<*>) = sequentialAp + +instance Monad (Sequential Semigroup.Last) where + (>>=) = sequentialBind + +instance Normal Semigroup.Last + +-- `Max` is a commutative duoidal functor + +instance Applicative (Parallel Max) where + pure = normalPure + (<*>) = commutativeAp + +instance Applicative (Sequential Max) where + pure = sequentialPure + (<*>) = sequentialAp + +instance Monad (Sequential Max) where + (>>=) = sequentialBind + +instance Normal Max + +-- `Maybe` is a commutative duoidal functor + +instance Applicative (Parallel Maybe) where + pure = normalPure + (<*>) = commutativeAp + +instance Applicative (Sequential Maybe) where + pure = sequentialPure + (<*>) = sequentialAp + +instance Monad (Sequential Maybe) where + (>>=) = sequentialBind + +instance Normal Maybe + +-- `Min` is a commutative duoidal functor + +instance Applicative (Parallel Min) where + pure = normalPure + (<*>) = commutativeAp + +instance Applicative (Sequential Min) where + pure = sequentialPure + (<*>) = sequentialAp + +instance Monad (Sequential Min) where + (>>=) = sequentialBind + +instance Normal Min + +-- `Monoid.Product` is a commutative duoidal functor + +instance Applicative (Parallel Monoid.Product) where + pure = normalPure + (<*>) = commutativeAp + +instance Applicative (Sequential Monoid.Product) where + pure = sequentialPure + (<*>) = sequentialAp + +instance Monad (Sequential Monoid.Product) where + (>>=) = sequentialBind + +instance Normal Monoid.Product + +-- `Proxy` is a commutative duoidal functor + +instance Applicative (Parallel Proxy) where + pure = normalPure + (<*>) = commutativeAp + +instance Applicative (Sequential Proxy) where + pure = sequentialPure + (<*>) = sequentialAp + +instance Monad (Sequential Proxy) where + (>>=) = sequentialBind + +instance Normal Proxy + +-- `Solo` is a commutative duoidal functor + +instance Applicative (Parallel Solo) where + pure = normalPure + (<*>) = commutativeAp + +instance Applicative (Sequential Solo) where + pure = sequentialPure + (<*>) = sequentialAp + +instance Monad (Sequential Solo) where + (>>=) = sequentialBind + +instance Normal Solo + +-- `Sum` is a commutative duoidal functor + +instance Applicative (Parallel Sum) where + pure = normalPure + (<*>) = commutativeAp + +instance Applicative (Sequential Sum) where + pure = sequentialPure + (<*>) = sequentialAp + +instance Monad (Sequential Sum) where + (>>=) = sequentialBind + +instance Normal Sum + +-- reader is a commutative duoidal functor + +instance Applicative (Parallel ((->) r)) where + pure = normalPure + (<*>) = commutativeAp + +instance Applicative (Sequential ((->) r)) where + pure = sequentialPure + (<*>) = sequentialAp + +instance Monad (Sequential ((->) r)) where + (>>=) = sequentialBind + +instance Normal ((->) r) + +-- Const + +instance (Monoid a) => Applicative (Parallel (Const a)) where + pure = normalPure + liftA2 f (Parallel a) (Parallel b) = Parallel $ liftA2 f a b + +instance (Monoid a) => Applicative (Sequential (Const a)) where + pure = Sequential . pure + liftA2 f (Sequential a) = Sequential . Base.liftA2 f a . getSequential + +-- | The `Const` duoidal functor provides an illustration of why we need to have +-- both `Parallel` and `Sequential` newtypes – relying on the underlying +-- `Applicative` (and only having the `Sequential` newtype) would mean that +-- any duoidal structure would only have a `Monad` available under +-- `Sequential`, which would be a prettty serious impact. On the other hand, +-- relying on the underlying `Monad` (and only having the `Parallel` newtype) +-- is much more natural, but `Const`, for example, having a `Monad` instance +-- would make it basically useless, and the more interesting `Applicative` +-- instance would only be available under the `Parallel` netwype. The current +-- structure allows either the `Applicative` or `Monad` instance to be the one +-- exposed directly. +instance (Monoid a) => Monad (Sequential (Const a)) where + Sequential (Const a) >>= _ = Sequential $ Const a + -- Either instance (Semigroup e) => Applicative (Parallel (Either e)) where @@ -509,7 +834,7 @@ instance (Semigroup e) => Applicative (Sequential (Either e)) where pure = sequentialPure - liftA2 = sequentialLiftA2 + (<*>) = sequentialAp instance (Semigroup e) => Monad (Sequential (Either e)) where (>>=) = sequentialBind @@ -539,7 +864,7 @@ instance Applicative (Sequential IO) where pure = sequentialPure - liftA2 = sequentialLiftA2 + (<*>) = sequentialAp instance Monad (Sequential IO) where (>>=) = sequentialBind @@ -584,3 +909,46 @@ -- | A writer is a `Normal` `Duoidal` functor when the writee is a -- `Duoid.Normal` `Duoid`. instance (Duoid.Normal a) => Normal ((,) a) + +instance (Duoid a, Duoid b) => Applicative (Parallel ((,,) a b)) where + pure = Parallel . (pempty,pempty,) + liftA2 f (Parallel (a, b, x)) (Parallel (a', b', y)) = + Parallel (a |-| a', b |-| b', f x y) + +instance (Duoid a, Duoid b) => Applicative (Sequential ((,,) a b)) where + pure = Sequential . (sempty,sempty,) + liftA2 = Base.liftM2 + +instance (Duoid a, Duoid b) => Monad (Sequential ((,,) a b)) where + Sequential (u, v, a) >>= k = + case k a of Sequential (u', v', b) -> Sequential (u >-> u', v >-> v', b) + +-- | A writer is a `Normal` `Duoidal` functor when the writee is a +-- `Duoid.Normal` `Duoid`. +instance (Duoid.Normal a, Duoid.Normal b) => Normal ((,,) a b) + +instance + (Duoid a, Duoid b, Duoid c) => + Applicative (Parallel ((,,,) a b c)) + where + pure = Parallel . (pempty,pempty,pempty,) + liftA2 f (Parallel (a, b, c, x)) (Parallel (a', b', c', y)) = + Parallel (a |-| a', b |-| b', c |-| c', f x y) + +instance + (Duoid a, Duoid b, Duoid c) => + Applicative (Sequential ((,,,) a b c)) + where + pure = Sequential . (sempty,sempty,sempty,) + liftA2 = Base.liftM2 + +instance (Duoid a, Duoid b, Duoid c) => Monad (Sequential ((,,,) a b c)) where + Sequential (u, v, w, a) >>= k = + case k a of + Sequential (u', v', w', b) -> Sequential (u >-> u', v >-> v', w >-> w', b) + +-- | A writer is a `Normal` `Duoidal` functor when the writee is a +-- `Duoid.Normal` `Duoid`. +instance + (Duoid.Normal a, Duoid.Normal b, Duoid.Normal c) => + Normal ((,,,) a b c)