diff --git a/CHANGELOG.md b/CHANGELOG.md new file mode 100644 --- /dev/null +++ b/CHANGELOG.md @@ -0,0 +1,18 @@ +# Changelog + +## [1.0.0] -- 2021-19-12 + +### Added + +- Initial release. Key features: + - Contravariant tracers, easily composable with parent context + - Concurrent-safe, simple, structured (JSON), stdout writer + - Generic definition of record of tracers for multi-component logging + +### Changed + +N/A + +### Removed + +N/A diff --git a/LICENSE b/LICENSE new file mode 100644 --- /dev/null +++ b/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/README.md b/README.md new file mode 100644 --- /dev/null +++ b/README.md @@ -0,0 +1,61 @@ +# contra-tracers + +## Overview + +An opinionated, simple and easy-to-use logging library leveraging contravariant functors to provide structured multi-component logger capability to real application. + +## Usage + +```hs +-- Some HTTP log message represented as Haskell values. + +data HttpLog + = SomeHttpLog + | SomeHttpWarning + deriving stock (Generic) + deriving anyclass (ToJSON) + +nstance HasSeverityAnnotation HttpLog + getSeverityAnnotation = \case + SomeHttpLog -> Info + SomeHttpWarning -> Warning + +-- Some DB log message represented as Haskell values. + +data DbLog = SomeDbLog + deriving stock (Generic) + deriving anyclass (ToJSON) + +nstance HasSeverityAnnotation HttpLog + getSeverityAnnotation = \case + SomeHttpLog -> Info + SomeHttpWarning -> Warning + +-- Applications tracers, defined as a record of higher-kinded types. We +-- have in particular 'TracerHKD Concrete a ~ a', which effectively makes +-- the 'Tracers' record a plain record of tracers once instantiated. + +data Tracers m (kind :: TracerDefinition) = Tracers + { tracerHttp :: TracerHKD kind (Tracer m HttpLog) + , tracerDb :: TracerHKD kind (Tracer m DbLog) + } deriving stock (Generic) + +-- The default configuration, setting all tracers to 'Info' min severity. +-- In practice, you may want to obtain the configuration from a config +-- file or from command-line options. +emptyConfiguration :: Tracers m MinSeverities +emptyConfiguration = defaultTracers Info + +main :: IO () +main = do + withStdoutTracer mempty emptyConfiguration $ \tracers -> do + concurrently_ + (myHttpApplication (tracerHttp tracers)) + (myDbApplication (tracerDb tracers)) +``` + +

+ :gift: Contributing + | + :floppy_disk: Changelog +

diff --git a/contra-tracers.cabal b/contra-tracers.cabal new file mode 100644 --- /dev/null +++ b/contra-tracers.cabal @@ -0,0 +1,79 @@ +cabal-version: 1.12 + +-- This file has been generated from package.yaml by hpack version 0.34.4. +-- +-- see: https://github.com/sol/hpack + +name: contra-tracers +version: 1.0.0 +synopsis: A logging library built on top of contra-tracer to make configuring and declaring multiple tracers easy (via generics). +description: Please see the README on GitHub at +category: Logging, Contravariant, Generics +homepage: https://github.com/cardanosolutions/ogmios#readme +bug-reports: https://github.com/cardanosolutions/ogmios/issues +author: KtorZ +maintainer: matthias.benkort@gmail.com +copyright: 2021 KtorZ +license: MPL-2.0 +license-file: LICENSE +build-type: Simple +extra-source-files: + LICENSE + README.md + CHANGELOG.md + +source-repository head + type: git + location: https://github.com/cardanosolutions/ogmios + +library + exposed-modules: + Data.Generics.Tracers + Data.Severity + other-modules: + Paths_contra_tracers + hs-source-dirs: + src + default-extensions: + BangPatterns + BinaryLiterals + ConstraintKinds + DataKinds + DefaultSignatures + DeriveDataTypeable + DeriveFoldable + DeriveFunctor + DeriveGeneric + DeriveTraversable + EmptyDataDecls + ExistentialQuantification + FlexibleContexts + FlexibleInstances + FunctionalDependencies + GADTs + InstanceSigs + KindSignatures + LambdaCase + MultiParamTypeClasses + MultiWayIf + NamedFieldPuns + NoImplicitPrelude + NumericUnderscores + OverloadedStrings + PartialTypeSignatures + PatternGuards + RankNTypes + ScopedTypeVariables + StandaloneDeriving + TupleSections + TypeFamilies + TypeSynonymInstances + ViewPatterns + ghc-options: -Wall -Wcompat -Widentities -Wincomplete-record-updates -Wincomplete-uni-patterns -Wpartial-fields -Wredundant-constraints -Wunused-packages + build-depends: + aeson + , base >=4.7 && <5 + , contra-tracer + if true + ghc-options: -O2 + default-language: Haskell2010 diff --git a/src/Data/Generics/Tracers.hs b/src/Data/Generics/Tracers.hs new file mode 100644 --- /dev/null +++ b/src/Data/Generics/Tracers.hs @@ -0,0 +1,185 @@ +-- 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/. + +{-# LANGUAGE TypeOperators #-} + +{-# OPTIONS_GHC -fno-warn-unticked-promoted-constructors #-} +{-# OPTIONS_HADDOCK prune #-} + +-- | This module provides a way to generically define and configure multiple +-- tracers for multiple logging components. +-- +-- This is useful in order to associate separate configuration (e.g. minimum +-- severity) to tracers corresponding to different parts of an application. For +-- example, in a webserver, one may imagine wanting to lower the verbosity of a +-- tracer used for all HTTP requests, but keep the database tracer at a debug +-- level. +-- +-- While this is possible to do without generics, it usually requires a bit of +-- boilerplate and repetitions. This module makes it easy to define one-single +-- data object as a record, for representing both severities configurations and +-- concrete instantiated tracers. Type signatures are a bit frightening, but the +-- usage is pretty simple (see 'Control.Tracer' for examples) +-- +module Data.Generics.Tracers + ( -- * Definition + IsRecordOfTracers + , TracerDefinition (..) + , type TracerHKD + + -- * Construction + , configureTracers + , defaultTracers + + -- Internal + , SomeMsg (..) + ) where + +import Prelude + +import GHC.Generics + +import Control.Tracer + ( Tracer (..), nullTracer ) +import Data.Aeson + ( ToJSON (..) ) +import Data.Functor.Const + ( Const (..) ) +import Data.Functor.Contravariant + ( contramap ) +import Data.Kind + ( Type ) +import Data.Severity + ( HasSeverityAnnotation (..), Severity ) + +-- * Definition + +-- | A constraint-alias defining generic record of tracers. +type IsRecordOfTracers tracers m = + ( GConfigureTracers m (Rep (tracers m MinSeverities)) (Rep (tracers m Concrete)) + , Generic (tracers m MinSeverities) + , Generic (tracers m Concrete) + ) + +-- | A data kind to control what's defined in a generic record of tracer. +-- +-- Use 'configureTracers' to turn a record of configuration into a record of +-- concrete tracers. +data TracerDefinition = Concrete | MinSeverities + +-- | A high-kinded type family to make definitions of tracers more readable. For +-- example, one can define a multi-component set of tracers as such: +-- +-- data Tracers m (kind :: TracerDefinition) = Tracers +-- { tracerHttp :: TracerHKD kind (Tracer m HttpLog) +-- , tracerStart :: TracerHKD kind (Tracer m StartLog) +-- } +type family TracerHKD (definition :: TracerDefinition) (tracer :: Type) :: Type where + TracerHKD MinSeverities tracer = Const (Maybe Severity) tracer + TracerHKD Concrete tracer = tracer + +-- * Construction + +-- | Convert a 'MinSeverities' of tracers into a 'Concrete' record of tracers, +-- using a base opaque 'Tracer'. +configureTracers + :: ( IsRecordOfTracers tracers m ) + => tracers m MinSeverities + -> Tracer m SomeMsg + -> tracers m Concrete +configureTracers f tr = + to . gConfigureTracers mempty tr . from $ f + +class GConfigureTracers m (f :: Type -> Type) (g :: Type -> Type) where + gConfigureTracers + :: String + -> Tracer m SomeMsg + -> f (Const (Maybe Severity) tr) + -> g tr + +instance GConfigureTracers m f g => GConfigureTracers m (D1 c f) (D1 c g) where + gConfigureTracers field tr = M1 . gConfigureTracers field tr . unM1 + +instance GConfigureTracers m f g => GConfigureTracers m (C1 c f) (C1 c g) where + gConfigureTracers field tr = M1 . gConfigureTracers field tr . unM1 + +instance (Selector s, GConfigureTracers m f g) => GConfigureTracers m (S1 s f) (S1 s g) where + gConfigureTracers _ tr = M1 . gConfigureTracers field tr . unM1 + where + field = selName (undefined :: S1 s f a) + +instance (GConfigureTracers m f0 g0, GConfigureTracers m f1 g1) + => GConfigureTracers m (f0 :*: f1) (g0 :*: g1) + where + gConfigureTracers field tr (f0 :*: f1) = + gConfigureTracers field tr f0 + :*: + gConfigureTracers field tr f1 + +instance (ToJSON msg, HasSeverityAnnotation msg, Applicative m) + => GConfigureTracers m (K1 i (Const (Maybe Severity) (Tracer m msg))) (K1 i (Tracer m msg)) + where + gConfigureTracers field tr = \case + K1 (Const (Just minSeverity)) -> + K1 (contramap (SomeMsg minSeverity field) tr) + K1 (Const Nothing) -> + K1 nullTracer + +-- | Assign a default value to a record of tracers. +-- +-- This is useful when used in conjunction with 'Const' and a record of tracer +-- severities: +-- +-- defaultTracers Info == Tracers +-- { tracerHttp = Const (Just Info) +-- , tracerDb = Const (Just Info) +-- } +-- +defaultTracers + :: forall tracers (m :: Type -> Type). + ( Generic (tracers m MinSeverities) + , GDefaultRecord (Rep (tracers m MinSeverities)) + , GDefaultRecordType (Rep (tracers m MinSeverities)) ~ Maybe Severity + ) + => Maybe Severity + -> tracers m MinSeverities +defaultTracers = + to . gDefaultRecord + +-- | This generic class allows for defining a default value to a record of +-- functors wrapping some type 'a'. +class GDefaultRecord (f :: Type -> Type) where + type GDefaultRecordType f :: Type + gDefaultRecord :: GDefaultRecordType f -> f (Const (GDefaultRecordType f) b) + +instance GDefaultRecord f => GDefaultRecord (D1 c f) where + type GDefaultRecordType (D1 c f) = GDefaultRecordType f + gDefaultRecord a = M1 (gDefaultRecord a) + +instance GDefaultRecord f => GDefaultRecord (C1 c f) where + type GDefaultRecordType (C1 c f) = GDefaultRecordType f + gDefaultRecord a = M1 (gDefaultRecord a) + +instance GDefaultRecord f => GDefaultRecord (S1 c f) where + type GDefaultRecordType (S1 c f) = GDefaultRecordType f + gDefaultRecord a = M1 (gDefaultRecord a) + +instance (GDefaultRecord f, GDefaultRecord g, GDefaultRecordType f ~ GDefaultRecordType g) => GDefaultRecord (f :*: g) where + type GDefaultRecordType (f :*: g) = GDefaultRecordType f + gDefaultRecord a = gDefaultRecord a :*: gDefaultRecord a + +instance GDefaultRecord (K1 i (Const a b)) where + type GDefaultRecordType (K1 i (Const a b)) = a + gDefaultRecord a = K1 (Const a) + +-- Internal + +-- A GADT capturing constraints as existential. +data SomeMsg where + SomeMsg + :: forall msg. (ToJSON msg, HasSeverityAnnotation msg) + => Severity + -> String + -> msg + -> SomeMsg diff --git a/src/Data/Severity.hs b/src/Data/Severity.hs new file mode 100644 --- /dev/null +++ b/src/Data/Severity.hs @@ -0,0 +1,49 @@ +-- 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/. + +{-# LANGUAGE DeriveAnyClass #-} +{-# LANGUAGE DerivingStrategies #-} + +module Data.Severity + ( Severity (..) + , HasSeverityAnnotation (..) + ) where + +import Prelude + +import Data.Aeson + ( FromJSON, ToJSON ) +import GHC.Generics + ( Generic ) + +-- | Define a log-level severity. +-- +-- +----------+----------------------------------------------------------------------------------+ +-- | Severity | Semantic | +-- +==========+==================================================================================+ +-- | Debug | Messages that contain information normally of use only when debugging a program. | +-- | Info | Informational messages. | +-- | Notice | Normal but significant conditions. | +-- | Warning | A situation that may become an error. | +-- | Error | Unexpected problem. | +-- +----------+----------------------------------------------------------------------------------+ +-- +data Severity + = Debug + | Info + | Notice + | Warning + | Error + deriving stock (Generic, Eq, Ord, Enum, Bounded, Show, Read) + deriving anyclass (ToJSON, FromJSON) + +-- | Associate a 'Severity' to a typed log message. +-- +-- data MyLog = MyLog +-- instance HasSeverityAnnotation MyLog where +-- getSeverityAnnotation = \case +-- MyLog -> Info +-- +class HasSeverityAnnotation a where + getSeverityAnnotation :: a -> Severity