coot/free-category
1
1
Fork 0
mirror of https://github.com/coot/free-category.git synced 2024-11-22 16:22:05 +03:00
Code Issues Projects Releases Wiki Activity

Lifting (#2)

Browse Source 
* Initial LoginStateMachine implementation

* Nicer interface

* Lifting instance for (->) and Identity, liftKleisli function

* Added Control.Category.Lifting to free-algebras

* Reoder Lifting module

* Fixed haddoc documentation

* examples.cabal - base version

* reconfigure circle-ci

* Fixed error in GHC-8.6.1
This commit is contained in:
Marcin Szamotulski 2018-12-10 19:59:39 +01:00 committed by GitHub
parent 34d9b45c07
commit 62d0bbe4fe
No known key found for this signature in database
GPG Key ID: 4AEE18F83AFDEB23
14 changed files with 737 additions and 51 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

38
.circleci/config.yml
View File

@ -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:

2
cabal.project Normal file
View File

@ -0,0 +1,2 @@
packages: .
./examples

8
default.nix
View File

@ -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; }

5
examples/CHANGELOG.md Normal file
View File

@ -0,0 +1,5 @@
# Revision history for examples
## 0.1.0.0 -- YYYY-mm-dd
* First version. Released on an unsuspecting world.

373
examples/LICENSE Normal file
View File

@ -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.

2
examples/Setup.hs Normal file
View File

@ -0,0 +1,2 @@
import Distribution.Simple
main = defaultMain

31
examples/examples.cabal Normal file
View File

@ -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

21
examples/pkg.nix Normal file
View File

@ -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;
}

163
examples/src/LoginStateMachine.hs Normal file
View File

@ -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)

37
free-category.cabal
View File

@ -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

4
nix/free-algebras.nix
View File

@ -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

5
shell.nix
View File

@ -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;
}

20
src/Control/Category/Free.hs
View File

@ -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

79
src/Control/Category/Lifting.hs Normal file
View File

@ -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)