diff --git a/.circleci/config.yml b/.circleci/config.yml index a8f7976..230ddf2 100644 --- a/.circleci/config.yml +++ b/.circleci/config.yml @@ -39,33 +39,53 @@ jobs: - setup - run: name: "GHC 861" - command: - nix-build --argstr compiler ghc861 - - cachix-push + command: | + nix-build -A free-category -o result-fc --argstr compiler ghc861 + nix-build -A examples -o result-ex --argstr compiler ghc861 + - cachix-push: + o: result-fc + - cachix-push: + o: result-ex GHC844: <<: *defaults steps: - setup - run: name: "GHC 844" - command: nix-build --argstr compiler ghc844 - - cachix-push + command: | + nix-build -A free-category -o result-fc --argstr compiler ghc844 + nix-build -A examples -o result-ex --argstr compiler ghc844 + - cachix-push: + o: result-fc + - cachix-push: + o: result-ex GHC822: <<: *defaults steps: - setup - run: name: "GHC 822" - command: nix-build --argstr compiler ghc822 - - cachix-push + command: | + nix-build -A free-category -o result-fc --argstr compiler ghc822 + nix-build -A examples -o result-ex --argstr compiler ghc822 + - cachix-push: + o: result-fc + - cachix-push: + o: result-ex + GHC802: <<: *defaults steps: - setup - run: name: "GHC 802" - command: nix-build --argstr compiler ghc802 - - cachix-push + command: | + nix-build -A free-category -o result-fc --argstr compiler ghc802 + nix-build -A examples -o result-ex --argstr compiler ghc802 + - cachix-push: + o: result-fc + - cachix-push: + o: result-ex workflows: build: diff --git a/cabal.project b/cabal.project new file mode 100644 index 0000000..f3f3de4 --- /dev/null +++ b/cabal.project @@ -0,0 +1,2 @@ +packages: . + ./examples diff --git a/default.nix b/default.nix index b3cbb90..82ab983 100644 --- a/default.nix +++ b/default.nix @@ -25,6 +25,10 @@ let else nixpkgs.lib.id; free-category = doDev(doHaddock(doTest(doBench( - pkgs.${compiler}.callPackage ./pkg.nix { inherit nixpkgs; })))); + pkgs.${compiler}.callPackage ./pkg.nix + { inherit nixpkgs; })))); + examples = doDev(doHaddock(doTest(doBench( + pkgs.${compiler}.callPackage ./examples/pkg.nix + { inherit free-category nixpkgs; })))); in -{ inherit free-category; } +{ inherit free-category examples; } diff --git a/examples/CHANGELOG.md b/examples/CHANGELOG.md new file mode 100644 index 0000000..77dfa36 --- /dev/null +++ b/examples/CHANGELOG.md @@ -0,0 +1,5 @@ +# Revision history for examples + +## 0.1.0.0 -- YYYY-mm-dd + +* First version. Released on an unsuspecting world. diff --git a/examples/LICENSE b/examples/LICENSE new file mode 100644 index 0000000..a612ad9 --- /dev/null +++ b/examples/LICENSE @@ -0,0 +1,373 @@ +Mozilla Public License Version 2.0 +================================== + +1. Definitions +-------------- + +1.1. "Contributor" + means each individual or legal entity that creates, contributes to + the creation of, or owns Covered Software. + +1.2. "Contributor Version" + means the combination of the Contributions of others (if any) used + by a Contributor and that particular Contributor's Contribution. + +1.3. "Contribution" + means Covered Software of a particular Contributor. + +1.4. "Covered Software" + means Source Code Form to which the initial Contributor has attached + the notice in Exhibit A, the Executable Form of such Source Code + Form, and Modifications of such Source Code Form, in each case + including portions thereof. + +1.5. "Incompatible With Secondary Licenses" + means + + (a) that the initial Contributor has attached the notice described + in Exhibit B to the Covered Software; or + + (b) that the Covered Software was made available under the terms of + version 1.1 or earlier of the License, but not also under the + terms of a Secondary License. + +1.6. "Executable Form" + means any form of the work other than Source Code Form. + +1.7. "Larger Work" + means a work that combines Covered Software with other material, in + a separate file or files, that is not Covered Software. + +1.8. "License" + means this document. + +1.9. "Licensable" + means having the right to grant, to the maximum extent possible, + whether at the time of the initial grant or subsequently, any and + all of the rights conveyed by this License. + +1.10. "Modifications" + means any of the following: + + (a) any file in Source Code Form that results from an addition to, + deletion from, or modification of the contents of Covered + Software; or + + (b) any new file in Source Code Form that contains any Covered + Software. + +1.11. "Patent Claims" of a Contributor + means any patent claim(s), including without limitation, method, + process, and apparatus claims, in any patent Licensable by such + Contributor that would be infringed, but for the grant of the + License, by the making, using, selling, offering for sale, having + made, import, or transfer of either its Contributions or its + Contributor Version. + +1.12. "Secondary License" + means either the GNU General Public License, Version 2.0, the GNU + Lesser General Public License, Version 2.1, the GNU Affero General + Public License, Version 3.0, or any later versions of those + licenses. + +1.13. "Source Code Form" + means the form of the work preferred for making modifications. + +1.14. "You" (or "Your") + means an individual or a legal entity exercising rights under this + License. For legal entities, "You" includes any entity that + controls, is controlled by, or is under common control with You. For + purposes of this definition, "control" means (a) the power, direct + or indirect, to cause the direction or management of such entity, + whether by contract or otherwise, or (b) ownership of more than + fifty percent (50%) of the outstanding shares or beneficial + ownership of such entity. + +2. License Grants and Conditions +-------------------------------- + +2.1. Grants + +Each Contributor hereby grants You a world-wide, royalty-free, +non-exclusive license: + +(a) under intellectual property rights (other than patent or trademark) + Licensable by such Contributor to use, reproduce, make available, + modify, display, perform, distribute, and otherwise exploit its + Contributions, either on an unmodified basis, with Modifications, or + as part of a Larger Work; and + +(b) under Patent Claims of such Contributor to make, use, sell, offer + for sale, have made, import, and otherwise transfer either its + Contributions or its Contributor Version. + +2.2. Effective Date + +The licenses granted in Section 2.1 with respect to any Contribution +become effective for each Contribution on the date the Contributor first +distributes such Contribution. + +2.3. Limitations on Grant Scope + +The licenses granted in this Section 2 are the only rights granted under +this License. No additional rights or licenses will be implied from the +distribution or licensing of Covered Software under this License. +Notwithstanding Section 2.1(b) above, no patent license is granted by a +Contributor: + +(a) for any code that a Contributor has removed from Covered Software; + or + +(b) for infringements caused by: (i) Your and any other third party's + modifications of Covered Software, or (ii) the combination of its + Contributions with other software (except as part of its Contributor + Version); or + +(c) under Patent Claims infringed by Covered Software in the absence of + its Contributions. + +This License does not grant any rights in the trademarks, service marks, +or logos of any Contributor (except as may be necessary to comply with +the notice requirements in Section 3.4). + +2.4. Subsequent Licenses + +No Contributor makes additional grants as a result of Your choice to +distribute the Covered Software under a subsequent version of this +License (see Section 10.2) or under the terms of a Secondary License (if +permitted under the terms of Section 3.3). + +2.5. Representation + +Each Contributor represents that the Contributor believes its +Contributions are its original creation(s) or it has sufficient rights +to grant the rights to its Contributions conveyed by this License. + +2.6. Fair Use + +This License is not intended to limit any rights You have under +applicable copyright doctrines of fair use, fair dealing, or other +equivalents. + +2.7. Conditions + +Sections 3.1, 3.2, 3.3, and 3.4 are conditions of the licenses granted +in Section 2.1. + +3. Responsibilities +------------------- + +3.1. Distribution of Source Form + +All distribution of Covered Software in Source Code Form, including any +Modifications that You create or to which You contribute, must be under +the terms of this License. You must inform recipients that the Source +Code Form of the Covered Software is governed by the terms of this +License, and how they can obtain a copy of this License. You may not +attempt to alter or restrict the recipients' rights in the Source Code +Form. + +3.2. Distribution of Executable Form + +If You distribute Covered Software in Executable Form then: + +(a) such Covered Software must also be made available in Source Code + Form, as described in Section 3.1, and You must inform recipients of + the Executable Form how they can obtain a copy of such Source Code + Form by reasonable means in a timely manner, at a charge no more + than the cost of distribution to the recipient; and + +(b) You may distribute such Executable Form under the terms of this + License, or sublicense it under different terms, provided that the + license for the Executable Form does not attempt to limit or alter + the recipients' rights in the Source Code Form under this License. + +3.3. Distribution of a Larger Work + +You may create and distribute a Larger Work under terms of Your choice, +provided that You also comply with the requirements of this License for +the Covered Software. If the Larger Work is a combination of Covered +Software with a work governed by one or more Secondary Licenses, and the +Covered Software is not Incompatible With Secondary Licenses, this +License permits You to additionally distribute such Covered Software +under the terms of such Secondary License(s), so that the recipient of +the Larger Work may, at their option, further distribute the Covered +Software under the terms of either this License or such Secondary +License(s). + +3.4. Notices + +You may not remove or alter the substance of any license notices +(including copyright notices, patent notices, disclaimers of warranty, +or limitations of liability) contained within the Source Code Form of +the Covered Software, except that You may alter any license notices to +the extent required to remedy known factual inaccuracies. + +3.5. Application of Additional Terms + +You may choose to offer, and to charge a fee for, warranty, support, +indemnity or liability obligations to one or more recipients of Covered +Software. However, You may do so only on Your own behalf, and not on +behalf of any Contributor. You must make it absolutely clear that any +such warranty, support, indemnity, or liability obligation is offered by +You alone, and You hereby agree to indemnify every Contributor for any +liability incurred by such Contributor as a result of warranty, support, +indemnity or liability terms You offer. You may include additional +disclaimers of warranty and limitations of liability specific to any +jurisdiction. + +4. Inability to Comply Due to Statute or Regulation +--------------------------------------------------- + +If it is impossible for You to comply with any of the terms of this +License with respect to some or all of the Covered Software due to +statute, judicial order, or regulation then You must: (a) comply with +the terms of this License to the maximum extent possible; and (b) +describe the limitations and the code they affect. Such description must +be placed in a text file included with all distributions of the Covered +Software under this License. Except to the extent prohibited by statute +or regulation, such description must be sufficiently detailed for a +recipient of ordinary skill to be able to understand it. + +5. Termination +-------------- + +5.1. The rights granted under this License will terminate automatically +if You fail to comply with any of its terms. However, if You become +compliant, then the rights granted under this License from a particular +Contributor are reinstated (a) provisionally, unless and until such +Contributor explicitly and finally terminates Your grants, and (b) on an +ongoing basis, if such Contributor fails to notify You of the +non-compliance by some reasonable means prior to 60 days after You have +come back into compliance. Moreover, Your grants from a particular +Contributor are reinstated on an ongoing basis if such Contributor +notifies You of the non-compliance by some reasonable means, this is the +first time You have received notice of non-compliance with this License +from such Contributor, and You become compliant prior to 30 days after +Your receipt of the notice. + +5.2. If You initiate litigation against any entity by asserting a patent +infringement claim (excluding declaratory judgment actions, +counter-claims, and cross-claims) alleging that a Contributor Version +directly or indirectly infringes any patent, then the rights granted to +You by any and all Contributors for the Covered Software under Section +2.1 of this License shall terminate. + +5.3. In the event of termination under Sections 5.1 or 5.2 above, all +end user license agreements (excluding distributors and resellers) which +have been validly granted by You or Your distributors under this License +prior to termination shall survive termination. + +************************************************************************ +* * +* 6. Disclaimer of Warranty * +* ------------------------- * +* * +* Covered Software is provided under this License on an "as is" * +* basis, without warranty of any kind, either expressed, implied, or * +* statutory, including, without limitation, warranties that the * +* Covered Software is free of defects, merchantable, fit for a * +* particular purpose or non-infringing. The entire risk as to the * +* quality and performance of the Covered Software is with You. * +* Should any Covered Software prove defective in any respect, You * +* (not any Contributor) assume the cost of any necessary servicing, * +* repair, or correction. This disclaimer of warranty constitutes an * +* essential part of this License. No use of any Covered Software is * +* authorized under this License except under this disclaimer. * +* * +************************************************************************ + +************************************************************************ +* * +* 7. Limitation of Liability * +* -------------------------- * +* * +* Under no circumstances and under no legal theory, whether tort * +* (including negligence), contract, or otherwise, shall any * +* Contributor, or anyone who distributes Covered Software as * +* permitted above, be liable to You for any direct, indirect, * +* special, incidental, or consequential damages of any character * +* including, without limitation, damages for lost profits, loss of * +* goodwill, work stoppage, computer failure or malfunction, or any * +* and all other commercial damages or losses, even if such party * +* shall have been informed of the possibility of such damages. This * +* limitation of liability shall not apply to liability for death or * +* personal injury resulting from such party's negligence to the * +* extent applicable law prohibits such limitation. Some * +* jurisdictions do not allow the exclusion or limitation of * +* incidental or consequential damages, so this exclusion and * +* limitation may not apply to You. * +* * +************************************************************************ + +8. Litigation +------------- + +Any litigation relating to this License may be brought only in the +courts of a jurisdiction where the defendant maintains its principal +place of business and such litigation shall be governed by laws of that +jurisdiction, without reference to its conflict-of-law provisions. +Nothing in this Section shall prevent a party's ability to bring +cross-claims or counter-claims. + +9. Miscellaneous +---------------- + +This License represents the complete agreement concerning the subject +matter hereof. If any provision of this License is held to be +unenforceable, such provision shall be reformed only to the extent +necessary to make it enforceable. Any law or regulation which provides +that the language of a contract shall be construed against the drafter +shall not be used to construe this License against a Contributor. + +10. Versions of the License +--------------------------- + +10.1. New Versions + +Mozilla Foundation is the license steward. Except as provided in Section +10.3, no one other than the license steward has the right to modify or +publish new versions of this License. Each version will be given a +distinguishing version number. + +10.2. Effect of New Versions + +You may distribute the Covered Software under the terms of the version +of the License under which You originally received the Covered Software, +or under the terms of any subsequent version published by the license +steward. + +10.3. Modified Versions + +If you create software not governed by this License, and you want to +create a new license for such software, you may create and use a +modified version of this License if you rename the license and remove +any references to the name of the license steward (except to note that +such modified license differs from this License). + +10.4. Distributing Source Code Form that is Incompatible With Secondary +Licenses + +If You choose to distribute Source Code Form that is Incompatible With +Secondary Licenses under the terms of this version of the License, the +notice described in Exhibit B of this License must be attached. + +Exhibit A - Source Code Form License Notice +------------------------------------------- + + This Source Code Form is subject to the terms of the Mozilla Public + License, v. 2.0. If a copy of the MPL was not distributed with this + file, You can obtain one at http://mozilla.org/MPL/2.0/. + +If it is not possible or desirable to put the notice in a particular +file, then You may include the notice in a location (such as a LICENSE +file in a relevant directory) where a recipient would be likely to look +for such a notice. + +You may add additional accurate notices of copyright ownership. + +Exhibit B - "Incompatible With Secondary Licenses" Notice +--------------------------------------------------------- + + This Source Code Form is "Incompatible With Secondary Licenses", as + defined by the Mozilla Public License, v. 2.0. diff --git a/examples/Setup.hs b/examples/Setup.hs new file mode 100644 index 0000000..9a994af --- /dev/null +++ b/examples/Setup.hs @@ -0,0 +1,2 @@ +import Distribution.Simple +main = defaultMain diff --git a/examples/examples.cabal b/examples/examples.cabal new file mode 100644 index 0000000..e64a0c4 --- /dev/null +++ b/examples/examples.cabal @@ -0,0 +1,31 @@ +-- Initial examples.cabal generated by cabal init. For further +-- documentation, see http://haskell.org/cabal/users-guide/ + +name: examples +version: 0.1.0.0 +-- synopsis: +-- description: +license: MPL-2.0 +license-file: LICENSE +author: Marcin Szamotulski +maintainer: profunctor@pm.me +-- copyright: +-- category: +build-type: Simple +extra-source-files: CHANGELOG.md +cabal-version: >=1.10 + +library + exposed-modules: LoginStateMachine + -- other-modules: + -- other-extensions: + build-depends: base >=4.9 && <5 + , free-category >= 0.0.1.0 + , free-algebras >= 0.0.7.0 + hs-source-dirs: src + default-language: Haskell2010 + ghc-options: -Wall + -fwarn-incomplete-record-updates + -fwarn-incomplete-uni-patterns + -fwarn-redundant-constraints + -fwarn-deprecations diff --git a/examples/pkg.nix b/examples/pkg.nix new file mode 100644 index 0000000..24169f5 --- /dev/null +++ b/examples/pkg.nix @@ -0,0 +1,21 @@ +{ nixpkgs +, mkDerivation +, base +, free-category +, free-algebras +, stdenv +}: +mkDerivation { + pname = "free-category-examples"; + version = "0.0.1.0"; + src = nixpkgs.lib.sourceFilesBySuffices ./. + [ ".hs" "LICENSE" "ChangeLog.md" "examples.cabal" ]; + libraryHaskellDepends = [ + base + free-category + free-algebras + ]; + libraryToolDepends = [ ]; + license = stdenv.lib.licenses.mpl20; + enableSeparateDocOutput = false; +} diff --git a/examples/src/LoginStateMachine.hs b/examples/src/LoginStateMachine.hs new file mode 100644 index 0000000..a3d64b8 --- /dev/null +++ b/examples/src/LoginStateMachine.hs @@ -0,0 +1,163 @@ +{-# LANGUAGE DataKinds #-} +{-# LANGUAGE GADTs #-} +{-# LANGUAGE KindSignatures #-} +{-# LANGUAGE NamedFieldPuns #-} +{-# LANGUAGE RankNTypes #-} +{-# LANGUAGE ScopedTypeVariables #-} +module LoginStateMachine where + +import Prelude hiding (id, (.)) + +import Control.Arrow (Kleisli (..)) +import Control.Category (Category (..)) + +import Control.Category.Free (Cat) + +-- Import classes and combintators used in this example +import Control.Category.Lifting + +{------------------------------------------------------------------------------- +-- Example State Machine, inspired by: +-- `State Machines All The Way Down` by Edwin Bradly, 2017 +-- https://www.youtube.com/watch?v=xq7ZuSRgCR4 +-------------------------------------------------------------------------------} + +data LoginResult = Success | LoginError + +-- | Type level representation of the states. +-- +data StateType where + LoggedInType :: StateType + LoggedOutType :: StateType + +data SStateType (a :: StateType) where + SLoggedIn :: SStateType 'LoggedInType + SLoggedOut :: SStateType 'LoggedOutType + +-- | Term level representation of the states. +-- @'LoggedOut'@ let one carry out a value. +-- +data State a (st :: StateType) where + LoggedIn :: State a 'LoggedInType + LoggedOut :: Maybe a -> State a 'LoggedOutType + +runLoggedOut :: State a 'LoggedOutType -> Maybe a +runLoggedOut (LoggedOut a) = a + +-- | Graph of transitions in the state machine. +-- In abstract representation the states do not show up, the only way to record +-- some data is to addit to the transition. Thus @'Logout'@ can carry data. +-- When interpreted in a some category (e.g. @'Kleisli' m@) then the data will +-- be avalable on @'LoggedOut{} :: 'State' a st@. +data Tr a from to where + Login :: SStateType to -> Tr a (State a 'LoggedOutType) (State a to) + Logout :: Maybe a -> Tr a (State a 'LoggedInType) (State a 'LoggedOutType) + Access :: Tr a (State a 'LoggedInType) (State a 'LoggedInType) + +login :: Monad m + => SStateType st + -> FreeLifting m (Cat (Tr a)) (State a 'LoggedOutType) (State a st) +login = liftCat . Login + +logout :: Monad m + => Maybe a + -> FreeLifting m (Cat (Tr a)) (State a 'LoggedInType) (State a 'LoggedOutType) +logout = liftCat . Logout + +access :: Monad m + => FreeLifting m (Cat (Tr a)) (State a 'LoggedInType) (State a 'LoggedInType) +access = liftCat Access + +type Username = String + +-- * Data representation of the state machine. + +newtype HandleLogin m authToken a = HandleLogin { + handleLogin :: authToken -> m (Maybe (HandleAccess m a)) + } + +data HandleAccess m a where + AccessHandler + :: m a -- access secret + -> (a -> m (HandleAccess m a)) -- handle secret + -> HandleAccess m a + LogoutHandler :: HandleAccess m a + +exampleHandleLogin + :: Applicative m + => String + -> HandleLogin m String String +exampleHandleLogin passwd = HandleLogin $ \authToken -> + if authToken == passwd + then pure (Just handleAccess) + else pure Nothing + where + handleAccess = AccessHandler (pure "secret") (\_ -> pure LogoutHandler) + + +-- * Abstract access function, also an isomorphism between @'HandleLogin' m a@ +-- and @'FreeLifting m (Tr a) (State a 'LoggedoutType) (State +-- a 'LoggedOutType). + +accessSecret + :: forall m authToken a. Monad m + => authToken + -> HandleLogin m authToken a + -> FreeLifting m (Cat (Tr a)) (State a 'LoggedOutType) (State a 'LoggedOutType) +accessSecret authToken HandleLogin{handleLogin} = lift $ do + st <- handleLogin authToken + case st of + Just accessHandler -> return $ handle accessHandler Nothing . login SLoggedIn + Nothing -> return id + where + handle :: HandleAccess m a -> Maybe a -> FreeLifting m (Cat (Tr a)) (State a 'LoggedInType) (State a 'LoggedOutType) + handle LogoutHandler ma = logout ma + handle (AccessHandler accessHandler dataHandler) _ = lift $ do + a <- accessHandler + accessHandler' <- dataHandler a + return $ handle accessHandler' (Just a) + +-- | Get data following the protocol defined by the state machine. +-- +-- Note: in GHC-8.6.1 we'd need @'MonadFail'@ which prevents from running this in +-- @'Identity'@ monad. To avoid this we use @'runLoggedOut'@ function. +getData + :: forall m authToken a. + ( Monad m ) + => (forall x y. Tr a x y -> Kleisli m x y) + -> HandleLogin m authToken a + -> authToken + -> m (Maybe a) +getData nat handleLogin authToken = case foldNatLift nat (accessSecret authToken handleLogin) of + Kleisli fn -> do + ma <- runLoggedOut <$> fn (LoggedOut Nothing) + return ma + +-- * Interpreters +-- To write an interpret it is enough to supply a natural transformation from +-- @'Tr' a from to@ to @'Kleisli' m@ for some monad @m@. + +-- | A pure natural transformation from @'Tr'@ to @'Kleisli' m@ for some +-- @'Monad' m@. Note, that even though @'Kleisli'@ category seems redundant +-- here, as we don't use the monad in the transformation, we need +-- a transformation into a category that satisfies the @'Lifing'@ constraint. +-- This is bause we will need the monad whn @'foldNatLift'@ will walk over the +-- constructors of '@FreeLifting'@ category. +-- +natPure :: forall m a from to. Monad m => Tr a from to -> Kleisli m from to +natPure = liftKleisli . nat + where + -- a natural trasformation to @'->'@ + nat :: Tr a from to -> (from -> to) + nat (Login SLoggedIn) = \_ -> LoggedIn + nat (Login SLoggedOut) = \_ -> (LoggedOut Nothing) + nat (Logout ma) = \_ -> (LoggedOut ma) + nat Access = \_ -> LoggedIn + +-- | A trivial program, which extracts a trivial secret. +main :: IO () +main = do + putStrLn "Provide a password:" + authToken <- getLine + secret <- getData natPure (exampleHandleLogin "password") authToken + putStrLn ("Secret: " ++ show secret) diff --git a/free-category.cabal b/free-category.cabal index 002836c..d8a078b 100644 --- a/free-category.cabal +++ b/free-category.cabal @@ -24,31 +24,32 @@ library exposed-modules: Control.Arrow.Free Control.Category.Free + Control.Category.Lifting other-modules: Paths_free_category hs-source-dirs: src default-extensions: - ConstraintKinds - DataKinds - DeriveFunctor - EmptyDataDecls - FlexibleInstances - FlexibleContexts - GADTs - KindSignatures - InstanceSigs - MultiParamTypeClasses - OverloadedStrings - PolyKinds - RankNTypes - ScopedTypeVariables - TupleSections - TypeApplications - TypeFamilies + ConstraintKinds + DataKinds + DeriveFunctor + EmptyDataDecls + FlexibleInstances + FlexibleContexts + GADTs + KindSignatures + InstanceSigs + MultiParamTypeClasses + OverloadedStrings + PolyKinds + RankNTypes + ScopedTypeVariables + TupleSections + TypeApplications + TypeFamilies build-depends: base >= 4.9 && <5 - , free-algebras >= 0.0.6.0 + , free-algebras >= 0.0.7.0 ghc-options: -Wall -fwarn-incomplete-record-updates diff --git a/nix/free-algebras.nix b/nix/free-algebras.nix index f83b5f1..6ca0a09 100644 --- a/nix/free-algebras.nix +++ b/nix/free-algebras.nix @@ -4,8 +4,8 @@ }: mkDerivation { pname = "free-algebras"; - version = "0.0.6.0"; - sha256 = "5a1d919b76fbe8697fae4c8d79ade62f9616ae44a1fa330aff415f352857628c"; + version = "0.0.7.0"; + sha256 = "f0c18b857087ec7ec0321f729562174c9a9f02172806e2fba7c8989fdd7631aa"; libraryHaskellDepends = [ base constraints containers data-fix dlist free groups kan-extensions mtl natural-numbers transformers diff --git a/shell.nix b/shell.nix index eb024a6..09fce56 100644 --- a/shell.nix +++ b/shell.nix @@ -1,4 +1,4 @@ -{ compiler ? "ghc843" +{ compiler ? "ghc844" , haddock ? true , test ? true , benchmarks ? false @@ -13,4 +13,7 @@ in free-category = if nixpkgs.lib.inNixShell then default.free-category.env else default.free-category; + examples = if nixpkgs.lib.inNixShell + then default.examples.env + else default.examples; } diff --git a/src/Control/Category/Free.hs b/src/Control/Category/Free.hs index cd590a1..78d997d 100644 --- a/src/Control/Category/Free.hs +++ b/src/Control/Category/Free.hs @@ -37,8 +37,6 @@ import Control.Arrow (Arrow (..), ArrowZero (..), ArrowChoice (..)) import Data.Monoid (Monoid (..)) import Data.Semigroup (Semigroup (..)) #endif -import Data.Monoid.MSet (MSet (..)) -import Data.Semigroup.SSet (SSet (..)) -- | -- Free category encoded as a recursive data type, in a simlar way as @@ -49,7 +47,7 @@ import Data.Semigroup.SSet (SSet (..)) -- -- The same performance concerns that apply to @'Control.Monad.Free.Free'@ -- apply to this encoding of a free category. -data Cat :: (* -> * -> *) -> * -> * -> * where +data Cat :: (k -> k -> *) -> k -> k -> * where Id :: Cat f a a (:.:) :: f b c -> Cat f a b -> Cat f a c @@ -86,14 +84,6 @@ instance Monoid (Cat f o o) where mappend = (<>) #endif -instance SSet (Cat f o o) (Cat f a o) where - act = (.) - -instance MSet (Cat f o o) (Cat f a o) where -#if __GLASGOW_HASKELL__ < 804 - mact = (.) -#endif - type instance AlgebraType0 Cat f = () type instance AlgebraType Cat c = Category c @@ -168,11 +158,3 @@ instance Monoid (C f o o) where #if __GLASGOW_HASKELL__ < 804 mappend = (<>) #endif - -instance SSet (C f o o) (C f a o) where - act = (.) - -instance MSet (C f o o) (C f a o) where -#if __GLASGOW_HASKELL__ < 804 - mact = (.) -#endif diff --git a/src/Control/Category/Lifting.hs b/src/Control/Category/Lifting.hs new file mode 100644 index 0000000..315a9a9 --- /dev/null +++ b/src/Control/Category/Lifting.hs @@ -0,0 +1,79 @@ +{-# LANGUAGE FunctionalDependencies #-} +module Control.Category.Lifting + ( Lifting (..) + , FreeLifting (..) + , liftCat + , foldNatLift + , liftKleisli + ) where + +import Prelude hiding (id, (.)) + +import Control.Arrow (Kleisli (..)) +import Control.Category (Category (..)) +import Data.Functor.Identity (Identity (..)) + +import Control.Category.Free (Cat (..)) +import Control.Algebra.Free2 (FreeAlgebra2 (..)) +import Data.Algebra.Free (AlgebraType, AlgebraType0, proof) + +-- | Categories which can lift monadic actions. +-- +class Category c => Lifting c m | c -> m where + lift :: m (c a b) -> c a b + +instance Monad m => Lifting (Kleisli m) m where + lift m = Kleisli (\a -> m >>= \(Kleisli f) -> f a) + +instance Lifting (->) Identity where + lift = runIdentity + +-- | Category transformer, which adds @'Lifting'@ instance to the underlying +-- base category. +data FreeLifting :: (* -> *) -> (k -> k -> *) -> k -> k -> * where + Base :: c a b -> FreeLifting m c a b + Lift :: m (FreeLifting m c a b) -> FreeLifting m c a b + +instance (Functor m, Category c) => Category (FreeLifting m c) where + id = Base id + Base f . Base g = Base $ f . g + f . Lift mg = Lift $ (f .) <$> mg + Lift mf . g = Lift $ (. g) <$> mf + +instance (Functor m, Category c) => Lifting (FreeLifting m c) m where + lift = Lift + +type instance AlgebraType0 (FreeLifting m) c = (Monad m, Category c) +type instance AlgebraType (FreeLifting m) c = Lifting c m +instance Monad m => FreeAlgebra2 (FreeLifting m) where + liftFree2 = Base + foldNatFree2 nat (Base cab) = nat cab + foldNatFree2 nat (Lift mcab) = lift $ foldNatFree2 nat <$> mcab + + codom2 = proof + forget2 = proof + +-- | Wrap a transition into a free category @'Cat'@ and then in +-- @'FreeLifting'@ +-- +-- prop> liftCat tr = Base (tr :.: Id) +-- +liftCat :: Monad m => tr a b -> FreeLifting m (Cat tr) a b +liftCat = liftFree2 . liftFree2 + +-- | Fold @'FreeLifing'@ category based on a free category @'Cat' tr@ using +-- a functor @tr x y -> c x y@. +-- +foldNatLift + :: (Monad m, Lifting c m) + => (forall x y. tr x y -> c x y) + -> FreeLifting m (Cat tr) a b + -> c a b +foldNatLift nat = foldNatFree2 (foldNatFree2 nat) + +-- | Functor from @'->'@ category to @'Kleisli' m@. If @m@ is @Identity@ then +-- it will respect @'lift'@ i.e. @lfitKleisli (lift ar) = lift (liftKleisli <$> +-- ar). +-- +liftKleisli :: Applicative m => (a -> b) -> Kleisli m a b +liftKleisli f = Kleisli (pure . f)