diff --git a/CHANGELOG.md b/CHANGELOG.md new file mode 100644 --- /dev/null +++ b/CHANGELOG.md @@ -0,0 +1,5 @@ +# Revision history for semigroupoids-do + +## 1.0 -- 2021-09-26 + +* First version. Released on an unsuspecting world. diff --git a/LICENSE.md b/LICENSE.md new file mode 100644 --- /dev/null +++ b/LICENSE.md @@ -0,0 +1,201 @@ +Apache License + Version 2.0, January 2004 + http://www.apache.org/licenses/ + + TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION + + 1. Definitions. + + "License" shall mean the terms and conditions for use, reproduction, + and distribution as defined by Sections 1 through 9 of this document. + + "Licensor" shall mean the copyright owner or entity authorized by + the copyright owner that is granting the License. + + "Legal Entity" shall mean the union of the acting entity and all + other entities that control, are controlled by, or are under common + control with that entity. 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This has a +range of uses; in our case, we are interested in being able to use do-notation +in a more general context than would normally be possible. + +[`semigroupoids`](https://hackage.haskell.org/package/semigroupoids) as a +package is designed to generalize certain common type classes, such as +`Applicative` and `Monad`. This can be convenient: for example, something could +be an `Apply` or `Bind`, but not an `Applicative` or `Monad` if no sensible +definition for `pure` exists. However, without the convenience of do-notation, +such instances mean significantly less, as they are awkward to use. This is an +unnecessary restriction at least in this example, as nothing about do-notation +requires `pure`. + +In this package, we provide a set of definitions suitable for use with +`QualifiedDo`, generalizing all the necessary operations to their +`semigroupoids` equivalents. Specifically: + +* It is now possible to use do-notation when you only have a + [`Bind`](https://hackage.haskell.org/package/semigroupoids-5.3.5/docs/Data-Functor-Bind.html#t:Bind). +* With `ApplicativeDo`, in some cases, you can use do-notation when you only + have an + [`Apply`](https://hackage.haskell.org/package/semigroupoids-5.3.5/docs/Data-Functor-Bind.html#t:Apply), + subject to the same conditions as using `Applicative` for do-notation. +* You can use refutable patterns when you only have + [`Plus`](https://hackage.haskell.org/package/semigroupoids-5.3.5/docs/Data-Functor-Plus.html#t:Plus). + +## What are the goals of this project? + +Our only goal is to provide `QualifiedDo` support for `semigroupoid` +generalizations; no more, no less. + +## How do I use this? + +```haskell +{-# LANGUAGE QualifiedDo #-} + +module MyModule where + +import Data.Functor.Bind (Bind) +import qualified Semigroupoids.Do as S + +foo :: (Bind m) => m a +foo = S.do + ... +``` + +## Wait, haven't I seen this somewhere before? + +You are probably thinking of +[`semigroupoids-syntax`](https://hackage.haskell.org/package/semigroupoids-syntax). +It is true that we take inspiration from it. However, we differ from it in a +couple of ways: + +* We only support the subset of syntax modification allowed by `QualifiedDo`; + `semigroupoids-syntax` goes beyond this, supplying a range of + `RebindableSyntax` capabilities. +* `semigroupoids-syntax` hasn't been updated since 2014. +* `semigroupoids-syntax` has support going back to much older GHCs; we limit + ourselves only to GHCs that have `QualifiedDo`. + +In short, this is a maintained, small, and simple package, to do only one task. + +## What does this run on? + +We support (and CI check) only those versions of GHC which support +`QualifiedDo`. Currently, that list is: + +* 9.0.1 + +We check on the following platforms: + +* Windows +* Linux +* MacOS + +## What can I do with this? + +The project is licensed Apache 2.0 (SPDX code +[`Apache-2.0`](https://spdx.org/licenses/Apache-2.0.html)). For more details, +please see the `LICENSE.md` file. diff --git a/Setup.hs b/Setup.hs new file mode 100644 --- /dev/null +++ b/Setup.hs @@ -0,0 +1,3 @@ +import Distribution.Simple + +main = defaultMain diff --git a/semigroupoids-do.cabal b/semigroupoids-do.cabal new file mode 100644 --- /dev/null +++ b/semigroupoids-do.cabal @@ -0,0 +1,42 @@ +cabal-version: 3.0 +name: semigroupoids-do +version: 1.0 +synopsis: Support for QualifiedDo with semigroupoids classes. +description: + Provides support for QualifiedDo using the more generalized type classes from + the semigroupoids package. + +homepage: https://github.com/kozross/semigroupoids-do +license: Apache-2.0 +license-file: LICENSE.md +author: Koz Ross +maintainer: koz.ross@retro-freedom.nz +bug-reports: https://github.com/kozross/semigroupoids-do/issues +copyright: (C) Koz Ross 2021 +category: Semigroupoids +tested-with: GHC ==9.0.1 +build-type: Simple +extra-source-files: + CHANGELOG.md + README.md + +-- Common section + +common lang + ghc-options: + -Wall -Wcompat -Wincomplete-record-updates + -Wincomplete-uni-patterns -Wredundant-constraints + -Wmissing-export-lists -Wmissing-deriving-strategies + + default-language: Haskell2010 + +-- Library + +library + import: lang + exposed-modules: Semigroupoids.Do + build-depends: + , base >=4.15 && <5 + , semigroupoids ^>=5.3.5 + + hs-source-dirs: src diff --git a/src/Semigroupoids/Do.hs b/src/Semigroupoids/Do.hs new file mode 100644 --- /dev/null +++ b/src/Semigroupoids/Do.hs @@ -0,0 +1,112 @@ +{-# LANGUAGE KindSignatures #-} +{-# LANGUAGE ScopedTypeVariables #-} + +-- | +-- Module: Semigroupoids.Do +-- Copyright: (C) Koz Ross 2021 +-- License: Apache 2.0 +-- Maintainer: koz.ross@retro-freedom.nz +-- Stability: Experimental +-- Portability: GHC only +-- +-- Provides definitions needed to use do-notation (by way of @QualifiedDo@) +-- using the more general type classes provided by @semigroupoids@. +-- +-- To use this module, enable @QualifiedDo@, import this module qualified, and +-- then prefix @do@ with the qualified name: +-- +-- > {-# LANGUAGE QualifiedDo #-} +-- > +-- > module MyModule where +-- > +-- > import Data.Functor.Bind (Bind) +-- > import qualified Semigroupoids.Do as S +-- > +-- > foo :: (Bind m) => m a +-- > foo = S.do +-- > ... +-- +-- This module is designed to work correctly (and similarly generally) with +-- @ApplicativeDo@ and @RecursiveDo@ (inasfar as that is possible). +module Semigroupoids.Do + ( (>>=), + (>>), + fail, + fmap, + (<*>), + join, + mfix, + return, + ) +where + +import Control.Monad.Fix (mfix) +import Data.Functor.Apply (Apply ((<.>))) +import Data.Functor.Bind (Bind ((>>-))) +import qualified Data.Functor.Bind as Bind +import Data.Functor.Plus (Plus (zero)) +import Data.Kind (Type) +import Prelude hiding + ( fail, + return, + (<*>), + (>>), + (>>=), + ) + +-- | @since 1.0 +(>>=) :: + forall (m :: Type -> Type) (a :: Type) (b :: Type). + (Bind m) => + m a -> + (a -> m b) -> + m b +(>>=) = (>>-) + +-- | @since 1.0 +(>>) :: + forall (m :: Type -> Type) (a :: Type) (b :: Type). + (Bind m) => + m a -> + m b -> + m b +x >> y = x >>- const y + +-- | = Important note +-- +-- This /ignores/ whatever 'String' you give it. It is a bad idea to use 'fail' +-- as a form of labelled error; instead, it should only be defaulted to when a +-- pattern match fails. +-- +-- @since 1.0 +fail :: + forall (m :: Type -> Type) (a :: Type). + (Plus m) => + String -> + m a +fail _ = zero + +-- | @since 1.0 +(<*>) :: + forall (f :: Type -> Type) (a :: Type) (b :: Type). + (Apply f) => + f (a -> b) -> + f a -> + f b +(<*>) = (<.>) + +-- | @since 1.0 +join :: + forall (m :: Type -> Type) (a :: Type). + (Bind m) => + m (m a) -> + m a +join = Bind.join + +-- | @since 1.0 +return :: + forall (f :: Type -> Type) (a :: Type). + (Applicative f) => + a -> + f a +return = pure