CHANGES.md

Version 2.0.0-RC1

2019 August 5

Cats 2.0.0-RC1 is the first release candidate for Cats 2.0, It's available on Scala 2.11, 2.12, 2.13.0 and Scala.js 0.6. Cats 2.0.0-RC1 (like the upcoming 2.0.0 release) maintains binary compatibility with Cats 1.x.x in the cats-kernel, cats-core and cats-free modules, but not cats-laws, cats-kernel-laws, cats-testkit, or alleycats.

2 breaking changes

• #2970 Decouple published modules from scalatest by @rossabaker
• #2896 replace Stream in ExhaustiveCheck with List by @kailuowang

1 bug fix

• #2942 fix Cofree.cata stack-safety #2940 by @road21

21 API/feature enhancements

• #2969 Add syntax to option. by @takayahilton
• #2964 Implement LazyList tailRecM using Iterator.unfold by @andyscott
• #2956 added Chain#takeWhile and Chain#dropWhile by @kailuowang
• #2953 Add method init and last to NonEmptyChain like NonEmptyList. by @takayahilton
• #2946 add unordered parallel variants of (flat)traverse and (flat)sequence by @mberndt123
• #2941 Added NonEmptyLazyList to replace NonEmptyStream by @kailuowang
• #2939 add map to NonEmptyChain. by @takayahilton
• #2929 Migrate to new kind-projector symbol by @LukaJCB
• #2925 Replace machinist macros by plain forwarders by @smarter
• #2924 More stack safety for IndexedReaderWriterStateT & IndexedStateT by @ybasket
• #2922 Reader contravariant on input type A by @kklorenzotesta
• #2917 Implement local for Reader by @jooohn
• #2916 Add listen for Writer and WriterT by @jooohn
• #2914 Fixed all 2.13 warnings, reenabled fatalWarning on 2.13 by @kailuowang
• #2913 Add LowerBounded and UpperBounded typeclasses by @izeigerman
• #2911 fixed more warnings on 2.13 by @kailuowang
• #2904 Cross compile replace Stream with LazyList on Scala 2.13 by @kailuowang
• #2895 Replace ⇒ with => to avoid Scala 2.13 warnings by @travisbrown
• #2889 Add missing factories similar to existing factories by @morgen-peschke
• #2880 Improve MonadError rethrow syntax to be more flexible by @bpholt
• #2787 Add Order instance for NonEmptySet (#2779) by @jatcwang

7 documentation improvements

• #2967 Fix FunctorFilter mapFilter doc example by @regadas
• #2966 add ContT to Data Types menu by @Jasper-M
• #2949 Update "README.md" for Scala 2.13.0 compiler specification changing(a… by @SeanDaru
• #2921 Fix typo in show.md by @ollyw
• #2888 Comonad documentation by @justinhj
• #2881 improve process document and release notes script by @kailuowang
• #2876 Fix typo by @asakaev

1 test improvement

• #2915 Add OrderTests for SortedSet by @jooohn

14 build improvements

• #2923 Update sbt-scalafmt to 2.0.2 by @scala-steward
• #2918 Update sbt-scala-native-crossproject, ... to 0.6.1 by @scala-steward
• #2912 Update sbt-microsites to 0.9.2 by @scala-steward
• #2908 Update sbt-scalafmt to 2.0.1 by @fthomas
• #2907 Update sbt-scalafix to 0.9.5 by @fthomas
• #2906 Update sbt-microsites to 0.9.1 by @scala-steward
• #2902 Update sbt-sonatype to 2.5 by @scala-steward
• #2901 Update sbt-scoverage to 1.6.0 by @scala-steward
• #2900 Update sbt-doctest to 0.9.5 by @scala-steward
• #2899 Update sbt-microsites to 0.7.27 by @scala-steward
• #2897 Update sbt-jmh to 0.3.7 by @scala-steward
• #2882 Update tut-plugin to 0.6.12 by @scala-steward
• #2828 make stage more explicit by @kailuowang

Version 2.0.0-M4

2019 June 11

Cats 2.0.0-M4 is a milestone release for Cats 2.0 that's available on Scala 2.11, 2.12, 2.13.0 and Scala.js 0.6. Cats 2.0.0-M4 (like the upcoming 2.0.0 release) maintains binary compatibility with Cats 1.x.x in the cats-kernel, cats-core and cats-free modules, but not cats-laws, cats-kernel-laws, cats-testkit, or alleycats.

2 documentation additions/fixes

• #2868 mention cats by example by @TomTriple
• #2860 Remove index.md from post-release process by @rossabaker

1 build improvements

• #2884 Upgrade Scala to 2.13.0 by @kailuowang

Version 1.6.1

2019 June 3

Cats 1.6.1 is binary compatible with all previous 1.x Cats releases.

2 API/Feature enhancements

• #2784 Make WrappedMutableMapBase extend Serializable by @ceedubs
• #2728 Optimize productR in Apply by @maphi

1 documentation addition/fix

• #2842 Fix Order.max and Oder.min description comments by @orvi

1 bug fix

• #2810 Change MonadErrorOps#reject so it no longer runs effects twice by @bplommer

Version 2.0.0-M3

2019 June 1

Cats 2.0.0-M3 is a milestone release for Cats 2.0 that's available on Scala 2.11, 2.12, 2.13.0-RC3 and Scala.js 0.6. Cats 2.0.0-M3 (like the upcoming 2.0.0 release) maintains binary compatibility with Cats 1.x.x in the cats-kernel, cats-core and cats-free modules, but not cats-laws, cats-kernel-laws, cats-testkit, or alleycats.

1 breaking change

• #2830 Remove deprecated cats.laws.discipline.eq methods (by @kailuowang).

1 source-breaking change

• #2843 Kleisli is now covariant in the input type (by @jcouyang).

1 documentation fix

• #2842 Fixes for API docs for Order methods (by @orvi).

3 build improvements

• #2869 Updates for 2.13.0-RC3 (by @travisbrown).
• #2865 Update sbt-hydra plugin (by @scala-steward).
• #2871 Remove closed-source sbt-hydra plugin (by @travisbrown).

Version 2.0.0-M2

2019 May 25

Cats 2.0.0-M2 is a milestone release for Cats 2.0. It's available on Scala 2.11, Scala 2.12, Scala 2.13.0-RC2 and Scala.js 0.6. Cats 2.0.0-M2 maintains binary compatibility on cats-kernel, cats-core and cats-free with Cats 1.x.x. Their 2.0.0-M2 jars are drop-in replacements for 1.0.1, 1.1.0, 1.2.0, 1.3.1, 1.4.0, 1.5.0, 1.6.0, and 2.0.0-M1 jars. cats-kernel, cats-core and cats-free 2.0.0 will remain binary compatible with 1.x. Cats 2.0.0-M2 breaks binary compatibility on cats-laws, cats-kernel-laws, cats-testkit and alleycats.

1 breaking change in cats-laws

• #2817 Added a new foldRight lazy law, move forallLazy and existLazy laws by @kailuowang

6 documentation additions/fixes

• #2855 Edit example in Parallel docs by @Jasper-M
• #2850 Small Readme fix by @dispalt
• #2819 added FreeT basic example by @mtsokol
• #2815 added navigation links to readme by @kailuowang
• #2813 Remove 'cats experimental' clause from README.md. by @kamilkloch
• #2811 added availability information by @kailuowang

3 API/Feature enhancements

• #2840 2708 sorted set semigroupal by @vladislavGutov
• #2837 Delete unnecessary restriction on biFlatMap by @AdrianRaFo
• #2796 Added collectFirst to Chain and NonEmptyChain by @LMnet

5 build improvements

• #2858 Don't create the hydra.license if $HydraLicense is empty by @dotta
• #2857 Updates for 2.13.0-RC2 by @travisbrown
• #2856 Update sbt-scalajs to 0.6.28 by @scala-steward
• #2848 Enables Hydra on cats build by @kailuowang
• #2821 removing unused resolver by @kailuowang

2 test improvements

• #2831 fixed applicative monoid test by @kailuowang
• #2827 In Apply.semigroup test replace ListWrapper with Option by @kailuowang

1 bug fix

• #2810 Change MonadErrorOps#reject so it no longer runs effects twice by @bplommer

Version 2.0.0-M1

2019 April 24

Cats 2.0.0-M1 is a milestone release for Cats 2.0. It's available on Scala 2.11, Scala 2.12, Scala 2.13.0-RC1 and Scala.js 0.6. Cats 2.0.0-M1 maintains binary compatibility on cats-kernel, cats-core and cats-free with Cats 1.x.x. Their 2.0.0-M1 jars are drop-in replacements for 1.0.1, 1.1.0, 1.2.0, 1.3.1, 1.4.0, 1.5.0 and 1.6.0 jars. cats-kernel, cats-core and cats-free 2.0.0 will remain binary compatible with 1.x. Cats 2.0.0-M1 breaks binary compatibility on cats-laws, cats-kernel-laws, cats-testkit and alleycats.

Breaking changes

• cats-laws and cats-kernel-laws now depend on ScalaCheck 1.14.0 which is not binary compatible with ScalaCheck 1.13.
• cats-testkit now depends on Scalatest 3.1.0-SNAP9 whics is not backward compatible with Scalatest 3.0.x.
• alleycats no longer supports export-hook.
• #2672 Alter from Reflexitivity to Reflexivity by @mattkohl
• #2640 Strong profunctor laws based on category theory by @lemastero

4 documentation additions/fixes

• #2803 Fix repetition in NonEmptyChain scala docs by @Obarros
• #2753 fix typo in faq.md by @xuwei-k
• #2736 Fix minor typo in parse-test-durations.awk example by @ceedubs
• #2722 Add more doctests to Kleisli by @nasadorian

18 API/Feature enhancements

• #2794 removed export hook by @kailuowang
• #2791 Remove catalysts dependency by @travisbrown
• #2785 Fix unconventional package objects in kernel by @denisrosca
• #2780 added foldF to EitherT by @kailuowang
• #2775 Distributive instance for Representable Functor by @catostrophe
• #2765 Define OptionT.mapFilter in terms of OptionT.subflatMap by @morgen-peschke
• #2760 Make MonoidK[Endo] stack safe on combineK by @denisrosca
• #2759 Category[Is] and related tests by @ctongfei
• #2750 Par functions for Bitraverse by @catostrophe
• #2747 add method on object CommutativeApplicative to get CommutativeMonoid by @alexeygorobets
• #2744 MonoidK instances for Map and SortedMap by @alexeygorobets
• #2728 Optimize productR in Apply by @maphi
• #2726 Add TraverseFilter instance for Set to alleycats by @dcastro
• #2724 adding helper method toFreeT to Free by @jcouyang
• #2711 Fixes #2631 Fix InvariantMonoidal Laws by @wojciechUrbanski
• #2709 Adds version of mkString_ with no prefix/suffix, matching the std lib. by @matthughes
• #2698 Add adaptErr to ApplicativeErrorOps by @bplommer
• #2696 Add a defer factory method to ContT by @cb372

15 build improvements

• #2806 update scalatest and discipline. by @kailuowang
• #2804 Update sbt-scala-native to 0.3.9 by @scala-steward
• #2797 Tuning JVM options for throughput by @DavidGregory084
• #2793 Update sbt-jmh to 0.3.6 by @scala-steward
• #2792 2.13.0-RC1 by @travisbrown
• #2786 Update tut-plugin to 0.6.11 by @scala-steward
• #2773 Update sbt-scalajs, scalajs-compiler to 0.6.27 by @scala-steward
• #2771 Fix our crossScalaVersions since the last change to travis.yml by @kailuowang
• #2764 Update sbt-jmh to 0.3.5 by @scala-steward
• #2762 Update sbt-travisci to 1.2.0 by @scala-steward
• #2752 added a styling stage to check the styles first by @kailuowang
• #2740 Update paradise to 2.1.1 by @scala-steward
• #2737 Experiment with modularizing Travis jobs by @ceedubs
• #2734 upgrade to scalacheck 1.14 by @kailuowang
• #2732 new better release settings by @kailuowang

3 test improvments

• #2672 Alter from Reflexitivity to Reflexivity by @mattkohl
• #2640 Strong profunctor laws based on category theory by @lemastero
• #2577 Don't depend on random sampling to determine function equivalence by @ceedubs

2 bug fixes

• #2784 Make WrappedMutableMapBase extend Serializable by @ceedubs
• #2735 Fix failing doctests by @ceedubs

Version 1.6.0

2019 Jan 31

Cats 1.6.0 is binary compatible with all previous 1.x Cats releases, i.e. its jar is a drop-in replacement for 1.0.1, 1.1.0, 1.2.0, 1.3.1, 1.4.0 and 1.5.0 jars. 1.6.0 is mostly identical to 1.6.0-RC1 except one additional feature enhancement.

• #2709 Adds version of mkString_ with no prefix/suffix, matching the std lib. by @matthughes

Version 1.6.0-RC1

2019 Jan 22

Cats 1.6.0-RC1 is binary compatible with all previous 1.x Cats releases, i.e. its jar is a drop-in replacement for 1.0.1, 1.1.0, 1.2.0, 1.3.1, 1.4.0 and 1.5.0 jars.

It brought you:

12 API/Feature enhancements

• #2641 Adding partitionEitherM by @blast-hardcheese
• #2609 Add an If-Then-Else operation to the Apply. by @diesalbla
• #2606 Add syntax for Bitraverse to allow traversal and sequencing of the left side by @andimiller
• #2600 Add sequenceFilter syntax by @kubukoz
• #2563 Add an applyK function to Kleisli. by @diesalbla
• #2450 Add Kleisli#mapK equivalent returning FunctionK by @kubukoz
• #2292 Add foldMapK, reduceMapK by @kubukoz
• #2693 Add IndexedState alias (#2686) by @valydia
• #2690 Override equals and hashCode on Chain by @ceedubs
• #2671 add syntax <&> for parallel by @jcouyang
• #2655 Add rethrowT method to EitherT by @bplommer
• #2647 Move cats.tests.ListWrapper to cats-testkit by @ArturGajowy

3 bug fixes

• #2702 Reverted binary incompatible changes to generated parallel syntax by @barambani
• #2692 Private val in value classes (Resolve TODO since 2.10 is dropped) by @barambani
• #2670 Issue 2657 - Ambiguous duration instances by @barambani

17 documentation additions/fixes

• #2642 Update table headers and clarify method signature for flatTap by @mtomko
• #2636 Some changes to glossary. by @diesalbla
• #2630 Fix a typo in Chain's doc by @satansk
• #2627 A bit clarification on PULL Request template by @kailuowang
• #2625 Fix type signature of productL in cats glossary by @mtomko
• #2622 Fix documented constraint on B param in foldMapM by @ksonj
• #2574 Remove duplicate menu item in docs by @petern-sc
• #2277 Add an explanation for the missing Applicative instances for monad transformers by @kubukoz
• #2700 update the copyright by @RafalSladek
• #2699 typo in Comanad[Try] by @philipschwarz
• #2684 Fix FAQ formatting error by @ceedubs
• #2677 Write documentation for ContT by @cb372
• #2668 Fix broken link to Arrow.scala by @DieBauer
• #2665 minor fix by @kailuowang
• #2664 Cleaning up docs to no longer use fine grained imports by @calvinbrown085
• #2659 change prePR to run BC test on Scala 2.11 build by @kailuowang
• #2656 Fix instructions for checking binary compatibility by @bplommer

10 build improvements

• #2637 Update kind-projector to 0.9.9 by @scala-steward
• #2619 Use composite projects by @Alistair-Johnson
• #2703 Update simulacrum to 0.15.0 by @scala-steward
• #2691 Don't send Gitter notifications for fork builds by @ceedubs
• #2681 Update sbt-release to 1.0.11 by @scala-steward
• #2674 minor fix to build by @kailuowang
• #2660 Update tut-plugin to 0.6.10 by @scala-steward
• #2654 Add a shell.nix and instructions for using it by @ceedubs
• #2652 Update SBT 1.2.7 by @ChristopherDavenport
• #2643 Update sbt-scalajs, scalajs-compiler, scalajs-library... to 0.6.26 by @scala-steward

Version 1.5.0

2018 Nov 30

Cats 1.5.0 is binary compatible with all previous 1.x Cats releases, i.e. its jar is a drop-in replacement for 1.0.1, 1.1.0, 1.2.0, 1.3.1 and 1.4.0 jars.

The artifacts are identical to Cats 1.5.0-RC1. For changes since 1.4.0 please check release notes of Cats 1.5.0-RC0 and Cats 1.5.0-RC1.

Version 1.5.0-RC1

2018 Nov 19

Cats 1.5.0-RC1 is binary compatible with all previous 1.x Cats releases, i.e. its jar is a drop-in replacement for 1.0.1, 1.1.0, 1.2.0, 1.3.1 and 1.4.0 jars.

It brought you:

5 API/Feature enhancements

• #2610 Expose headOption for Chain by @ChristopherDavenport
• #2596 Add standalone Try syntax import by @kubukoz
• #2594 Get FunctorFilter on par with the other MTL typeclasses by @barambani
• #2588 Add flap function to Apply by @ssanj
• #2506 Add ContT monad by @johnynek

1 test improvment

• #2578 Add awk script to parse test durations by @ceedubs

5 bug fixes

• #2618 Issue 2608 - Ambiguous implicit values for Functor[Kleisli[F, A, ?]] by @barambani
• #2617 Make the vals inside all 'Ops' style classes private by @coltfred
• #2615 2611 - MonadError syntax for OptionT uses incorrect instance by @barambani
• #2614 Make the value of the class private by @coltfred
• #2603 Rename EitherT.biflatMap by @ochrons

1 build improvement

• #2605 Reduce Xmx in .jvmopts and build.sbt by @Alistair-Johnson

Version 1.5.0-RC0

2018 Nov 8

Cats 1.5.0-RC0 is binary compatible with all previous 1.x Cats releases, i.e. its jar is a drop-in replacement for 1.0.1, 1.1.0, 1.2.0, 1.3.1 and 1.4.0 jars.

1.5.0-RC0 brought

23 API/Feature enhancements

• #2597 Optimize Apply methods in FlatMap by @kailuowang
• #2592 Add updateWith method to NonEmptyMap by @nasadorian
• #2579 Added Chain#distinct and NonEmptyChain#distinct to match List#distinct and NonEmptyList#distinct by @fmsbeekmans
• #2573 Add biFlatMap to EitherT by @agajek
• #2557 Add NonEmptyList#toNes (issue #2346) by @CucumisSativus
• #2555 Add OptionOps.toInvalidNec and OptionOps.toValidNec by @ybasket
• #2552 Optimize the foldM implementation for Vector by @ceedubs
• #2548 Missing Contravariant instance for OptionT by @barambani
• #2544 Adding FiniteDuration instances by @calvinbrown085
• #2543 Adding Nes and Nec equivalents of Nel functions by @calvinbrown085
• #2541 Add NonEmptyList#toNem (issue #2346) by @CucumisSativus
• #2535 Add NonEmptyMap#toNonEmptyList (issue #2346) by @CucumisSativus
• #2534 avoid deprecated macro APIs post 2.10 by @larsrh
• #2533 Add empty to State and StateT objects by @larsrh
• #2527 align type parameter of smart constructor with Validated (#2525) by @thoefer
• #2522 added Convenience functions for Ior NonEmptyChain by @binkabir
• #2521 fixed eqv alias issue #2513: by @binkabir
• #2520 Add count as syntax to UnorderedFoldable by @leusgalvan
• #2515 Add Duration Instances to cats.instances.all and cats.implicits by @LukaJCB
• #2511 .raiseError syntax allows an error subtype by @guersam
• #2510 Add Pure instance for Future by @danslapman
• #2487 Add toValidatedNec to Validated by @satansk
• #2475 Add Either#toEitherNel extension and friends by @kubukoz

1 bug fix

• #2586 UnorderedFoldable#isEmpty default implementation is incorrect by @barambani

16 documentation additions/fixes

• #2576 Contributing guidelines link by @fmsbeekmans
• #2572 Add Alternative docs by @stephen-lazaro
• #2566 Add Tuple2 Example for Bifunctor by @stephen-lazaro
• #2564 Fixed typo in the docs by @barambani
• #2558 Add Nomenclature / Cheatsheet page by @diesalbla
• #2554 Adding the cats friendly badge link to README by @calvinbrown085
• #2550 Proposal: add cats-collections as an external cats module by @kailuowang
• #2549 Add FAQ for monad transformer variance by @ceedubs
• #2547 Fix link for contributing documentation by @ceedubs
• #2537 Updating Year. by @shankarshastri
• #2528 fix typo in validated documentation by @ssanj
• #2524 cats logo as svg and new "cats friendly" badge by @thoefer
• #2512 Add definition of point-wise to README by @AaronDelaplane
• #2505 Add Chain docs by @LukaJCB
• #2472 Replace List with Chain in Validated's docs by @satansk
• #2459 Add documentation for FlatMap and Bifunctor by @asoltysik

20 build improvements

• #2591 Update tut-plugin to 0.6.9 by @scala-steward
• #2590 Update sbt-release to 1.0.10 by @scala-steward
• #2589 updated to 2.13-M5 by @kailuowang
• #2583 added a prePR command and PR template to remind people to run it by @kailuowang
• #2581 Fix test fork settings I think by @ceedubs
• #2568 give test more memory by @kailuowang
• #2565 Disable Scala Native build for kernel by @agajek
• #2562 Introduce Scalafmt by @joan38
• #2507 Update sbt to 1.2.3 by @fthomas
• #2503 Update sbt-jmh to 0.3.4 by @scala-steward
• #2502 Update tut-core to 0.6.7 by @scala-steward
• #2501 Update sbt-scala-native to 0.3.8 by @scala-steward
• #2499 Update sbt-crossproject to 0.6.0 by @scala-steward
• #2497 Update partial-unification to 1.1.2 by @scala-steward
• #2496 Update sbt-git to 1.0.0 by @scala-steward
• #2495 Update sbt-pgp to 1.1.2 by @scala-steward
• #2494 Update sbt-release to 1.0.9 by @scala-steward
• #2493 Update sbt-unidoc to 0.4.2 by @scala-steward
• #2492 Update sbt-travisci to 1.1.3 by @scala-steward
• #2382 Removed not used sbt-scala-native plugin and fixed importing the project into intellij by @LukaszMarchewka

2 test improvments

• #2523 Add doctests for Semigroup, Group, and Monoid enhancement by @DennisVDB
• #2509 Adding tests for binary compat that can't be tested by Mima by @kailuowang

Version 1.4.0

2018 Sep 12

Cats 1.4.0 is binary compatible with all previous 1.x Cats releases, i.e. its jar is a drop-in replacement for 1.0.1, 1.1.0, 1.2.0, and 1.3.1 jars. Cats 1.3.1 introduced an unnecessary runtime dependency (scala-collection-compat), this 1.4.0 release removes it.

1.4.0 also brought you:

2 Bug fixes

• #2488 Kill scala-collection-compat by @travisbrown
• #2423 Fix NestedIdOps.value leaking to types of shapes F[G[A]] by @zarthross

4 API Enhancements

• #2480 improve interaction with subtyping in OptionOps#liftTo by @mberndt123
• #2452 Add filterFold and collectFold to Foldable by @satansk
• #2426 Enrich return type for Representable.apply and add doctests by @ceedubs
• #2477 Add Order#fromLessThan by @vlovgr

7 Documentation Additions/Fixes

• #2485 Proposal - add cats-tagless as an external module by @kailuowang
• #2483 Add examples to Functor and verify with docstyle by @YuvalItzchakov
• #2481 moved a couple of ecosystem project to more accurate section by @kailuowang
• #2478 Made it slightly easier to add a Cats ecosystem project by @kailuowang
• #2476 add nezasa to adopters list by @rethab
• #2461 Fix typo in CHANGES by @asakaev
• #2234 Fix CONTRIBUTING docs by @asakaev

Version 1.3.1

2018 Sep 5

Cats 1.3.1 is binary compatible with all previous 1.x Cats releases, i.e. its jar is a drop-in replacement for 1.0.1, 1.1.0 and 1.2.0 jars. Cats 1.3.1 does not support Scala 2.10.

This is a bug fix release that fixed the binary compatibility breakage when summoning Monad[OptionT[F, ?]] in 1.3.0

Version 1.3.0

2018 Sep 4

Cats 1.3.0 is binary compatible with all previous 1.x Cats releases, i.e. its jar is a drop-in replacement for 1.0.1, 1.1.0 and 1.2.0 jars. There is a bug in this release that breaks binary compatibility when summoning Monad[OptionT[F, ?]]. Cats 1.3.0 does not support Scala 2.10.

1.3.0 brought you:

12 API Enhancements

• #2431 Give NonEmptyChain more presence by @LukaJCB
• #2421 Add/fix Foldable extensions: findM and collectFirstSomeM by @catostrophe
• #2416 add append method to NEL by @julien-truffaut
• #2406 Add NonEmptyChain by @LukaJCB
• #2405 Add FunctorFilter and TraverseFilter by @LukaJCB
• #2402 Add Compose instance for Map by @denisrosca
• #2371 Add Chain by @LukaJCB
• #2367 add Tuple2K#swap by @aoiroaoino
• #2366 Add Foldable extension collectFirstSomeM by @catostrophe
• #2351 Add parTraverse_ and parSequence_ syntax by @denisrosca
• #2345 Add one off object for importing lawless Map instances by @andyscott
• #2314 Adding on flatTransform to OptionT as suggested. by @abhishek7

1 Bug fix:

• #2383 Monad[Free[Id, ?]] cannot be found by @barambani

3 Code Cleanups

• #2451 Remove unnecessary semicolons by @satansk
• #2425 Override size in Chain instance by @ceedubs
• #2403 use as and void instead of map(_ => ) by @julien-truffaut

13 Documentation Additions/Fixes

• #2427 Add scaladoc example for Semigroupal.product by @ceedubs
• #2378 Fix typos detected by github.com/client9/misspell by @seratch
• #2377 Fix minor typos in typeclasses docs by @ksonj
• #2374 proofread: remove extra word by @jarrodu
• #2373 add new nested to menu by @kailuowang
• #2372 Add initial adopters list by @kubukoz
• #2369 Add a documentation page for Nested by @cb372
• #2368 fix typo by @letusfly85
• #2361 Make kittens officially a Cats module (still separate repo) by @kailuowang
• #2337 Update the outdated FAQ on IO/Task by @ceedubs
• #2344 Use sbt-doctest for Defer example by @ceedubs
• #2429 Replace all usage of the list Monoid in the docs with the chain Monoid by @jan0sch
• #2465 fix laws link in CONTRIBUTING by @melrief

7 Build and Tests Improvements:

• #2430 Make Chain Arbitraries recursively build concatenations by @johnynek
• #2420 Better Chain Arbitrary by @LukaJCB
• #2359 tweak a test to compile on latest Scala 2.13 nightlies by @SethTisue
• #2354 temporarily disable scaladoc on 2.13 by @kailuowang
• #2335 Updating to scala 2.13-M4 by @kailuowang
• #2306 Drop 2.10 support / update to 2.13-M4 by @larsrh
• ##2466 remove bench from release by @kailuowang

Version 1.2.0

Cats 1.2.0 is binary compatible with all previous 1.x Cats releases, i.e. its jar is a drop-in replacement for 1.0.1 and 1.1.0 jars.

Cats 1.2.0 is also the last non-patch release that supports Scala 2.10. Farewell Scala 2.10.

1.2.0 brought you:

24 API Enhancements

• #2329 Add Representable instance for Eval. by @denisrosca
• #2325 Add Cofree.ana and Cofree.anaEval. by @andyscott
• #2315 Add choice syntax. by @catostrophe
• #2299 2228-add MonadError instance for optionT where F is a Monad. by @heyrutvik
• #2297 Make cats.data.AndThen public. by @alexandru
• #2293 added liftTo syntax to Validated. by @kailuowang
• #2285 Add groupBy for NonEmptySet. by @Obarros
• #2284 Add Representable Functor enhancemen. by @eli
• #2279 Add Defer typeclass, laws and implementations. by @johnynek
• #2274 Adding biSemiflatMap to EitherT (#2269). by @ericaovo
• #2262 Add .nested syntax.. by @danielkarch
• #2259 Add a Binested data type. by @iravid
• #2258 updated trait ComposedFoldable in Composed.scala. by @Zhen
• #2256 Add .parFlatTraverse and .parFlatSequence syntax. by @Avasil
• #2253 Add .toOptionT to option syntax. by @marcodippy
• #2252 Add tapWithF to Kleisli. by @marcodippy
• #2249 Add some FlatMap loops useful for State and Effects. by @johnynek
• #2246 Use unit from Applicative. by @johnynek
• #2243 Add orElse to ApplicativeError. by @barambani
• #2232 Change override of neqv in Order. by @ceedubs
• #2219 Add Bimonad instance to NEL and NEV. by @LukaJCB
• #2217 Add dual categories.. by @sellout
• #2204 Added commutative apply and applicative to Const. by @barambani
• #2191 Extend Functor implementation in the Traverse instance of EitherT, OptionT and Tuple2K. by @barambani

22 Documentation Additions/Fixes

• #2330 Add droste to project list. by @andyscott
• #2311 Add Rainier to the cats library list. by @andyscott
• #2307 Specify the source of the autogenerated boilerplate. by @dadepo
• #2303 Change scaladoc link title to "API Documentation". by @Obarros
• #2291 Update Bitraverse docs. by @Zelenya
• #2280 add editor setup tips to contrib guide. by @eli
• #2278 Elaborate on Foldable#collectFirst comment. by @kubukoz
• #2270 markdown improvements. by @martijnhoekstra
• #2266 Update 'Scala with Cats' reference in docs. by @guersam
• #2251 Be more precise about left vs right in Foldable doc. by @ceedubs
• #2248 Update state.md. by @rsekulski
• #2247 Add fastparse-cats to the list of projects. by @johnynek
• #2245 clarify law testing's dependency on cats-testkit and scalates. by @kailuowang
• #2241 Added shims to the ecosystem list. by @djspiewak
• #2226 Slight clean up of State docs. by @ceedubs
• #2225 Add doctest example for groupByNel. by @ceedubs
• #2223 replace cats with Cats for consistency in README.md. by @satansk
• #2222 Port alleycats README.md from the defunct repo. by @longcao
• #2221 Update contributors guide. by @AlejandroME
• #2218 Remove extra 'a' in eithert.md. by @donaldosalas
• #2211 2.12.x no longer needs future-tense. by @mattkohl
• #2178 Add jump start guide. by @PawelLipski

12 Build and Tests Improvements:

• #2302 Update sbt-partial-unification with support for 2.13.0-M4. by @kailuowang
• #2301 sbt 1.1.6. by @sullis
• #2298 Replace to new jvm flag. by @jiminhsieh
• #2265 Add Function To Check All Relevant MiMa Versions. by @ChristopherDavenport
• #2264 update bin compat versions to 1.0.0 and 1.1.0. by @kailuowang
• #2260 Update Scala, sbt, and sbt plugins. by @fthomas
• #2206 upgraded scala 2.12.5. by @kailuowang
• #2205 Use helper addSbtCoursier in project/plugins.sbt. by @BennyHill
• #2203 Add support for 2.13.0-M3. by @BennyHill
• #2215 Test Show instance for Duration. by @ceedubs
• #2214 Check MonadTests for Vector and List. by @ceedubs
• #2213 Use poly lambda syntax in FreeApplicative test. @ceedubs

Version 1.1.0

Cats 1.1.0 is binary compatible with 1.0.1, i.e. its jar is a drop-in replacement for the 1.0.1 jar.

1.1.0 brought you:

15 API Enhancements

• #2194 Add reject (partial function) method to MonadError by @Wogan
• #2192 Add valueOrF to EitherT by @denisrosca
• #2183 Add parTuple by @barambani
• #2182 Add Foldable, Traverse and Comonad instances to WriterT by @barambani
• #2179 added liftTo to Try, Either and Option by @kailuowang
• #2169 Add FreeT.inject helper function (#1534) by @valydia
• #2159 Added Bitraverse for Ior (#2144) by @V-Lamp
• #2150 contravariant coyoneda by @tpolecat
• #2149 Add leftFlatMap to Either by @rohanshah
• #2146 added leftNel and rightNel syntax by @kailuowang
• #2143 Add NonEmptySet by @LukaJCB
• #2141 Add NonEmptyMap by @LukaJCB
• #2123 Add contains_, foldSmash and mkString_ to FoldableOps by @rsoeldner
• #2119 Fixes type params for OptionT.getOrElse(F) by @fcanedo
• #2076 Add Endo type alias for (A => A) by @kailuowang

4 Bug Fixes

• #2188 Remove calls to PartialFunction.apply, deprecated in 2.12.5 by @BennyHill
• #2187 Fix #2186: make IndexedStateT stack safe by @alexandru
• #2185 Fix #1733: make Kleisli.flatMap stack safe by @alexandru
• #2148 Add missing UnorderedTraverse syntax by @andyscott

16 Documentation Additions/Fixes

• #2196 Add "Law Testing" to side menu to increase visiblity. by @wjlow
• #2190 Add Ciris to list of projects in readme by @vlovgr
• #2184 Add Dsl.scala in the cats ecosystem by @Atry
• #2177 Docs: Updated typeclass instances table by @battermann
• #2171 adding validation video by @Andrea
• #2165 Add types in the Kleisli code sample for composition by @jcranky
• #2156 Fix Spooky scaladoc typo by @jcranky
• #2155 Fix broken link in parallel documentation by @allantl
• #2154 contravariant.md [reversing roles of A and B in commentary to match the code] by @phderome
• #2153 added ammonite instructions to faq by @kailuowang
• #2145 Update version in lawtesting docs by @LukaJCB
• #2140 Set micrositeDocumentationUrl as root-relative by @calvellido
• #2134 Minor scaladoc fix for ::: by @jcranky
• #2125 Wrong link in Eval doc by @gruggiero
• #2122 Add doctest example for ApplicativeError.raiseError by @ceedubs
• #1720 type classes with only defined laws to guideline by @kailuowang

4 Build Improvements:

• #2189 split build jvm,add workers to kernel by @BennyHill
• #2164 remove java 7 build by @xuwe
• #2158 update travis cache settings by @kailuowang
• #1919 update to sbt 1.0 by @kailuowang

Version 1.0.1

2017 Dec 31

There is zero code change since 1.0.0. This is a release to fix the 1.0.0-MF issue that on Maven 1.0.0-MF is deemed later than 1.0.0. For details see #2131

Version 1.0.0

2017 Dec 25

Documentation Improvements/Additions:

• #2121 Update deprecations to product{L,R} instead of ap{L,R} by @rossabaker
• #2086 Add doctest examples for Apply by @ceedubs
• #2080 Add grouping to scaladoc for arity methods by @ceedubs

Version 1.0.0-RC2

2017 Dec 18

Breaking changes and migration

• #2039 Remove Applicative#traverse and Applicative#sequence by @kubukoz
• #2033 standardise on liftF and add liftK to transformers by @SystemFw
• #2083 Change forEffect/followedBy to productL/productR by @Jacoby6000
• #2088 Add InvariantSemigroupal and ability to turn Monoidals to Monoids by @LukaJCB

New features / enhancements (API, instances, data types, etc.):

• #1949 Add ::: to NonEmptyList by @jcranky
• #2020 Add foldl and foldr aliases to Foldable by @felixmulder
• #2024 Optimize foldMap implementations with combineAll by @carymrobbins
• #1938 Add more Parallel instances by @LukaJCB
• #2030 added collectFirst and collectFirstSome to Foldable by @kailuowang
• #1977 Add Ior Monad Transformer by @frroliveira
• #2038 Add &> and <& as syntax for Parallel by @LukaJCB
• #1981 Add UnorderedFoldable and UnorderedTraverse by @LukaJCB
• #2047 CommutativeMonoid instance for SortedMap by @alonsodomin
• #2043 Removed deprecation of >> and changed its param to be a by-name by @mpilquist
• #2034 Add ContravariantMonoidal by @stephen-lazaro
• #2057 Add Ior.fromEither by @markus1189
• #2056 Functor.fmap by @fosskers
• #2059 Add Parallel instance for Ior by @andyscott
• #2061 Add MonadError.rethrow by @SystemFw
• #2072 added a default id for Arrow by @kailuowang
• #2063 Added merge (product) to Arrow for arrows composition by @marcobattaglia
• #2060 Add parallel instance for IorT by @andyscott
• #2046 Add distributive typeclass and some instances by @coltfred
• #2099 CommutativeMonad and CommutativeFlatMap instances for Tuple2 by @ceedubs
• #2096 Add Arrow Choice by @stephen-lazaro
• #2098 Add a CommutativeMonoid for Map by @ceedubs
• #2101 Add Semigroup.instance method by @jozic
• #2103 CommutativeMonad for Eval by @ceedubs
• #2104 Add Commutative{Monad, FlatMap} instances for IdT by @ceedubs
• #2105 Some Kleisli instance cleanup by @ceedubs
• #2110 add Comparison to cats package by @kailuowang
• #2112 CoflatMap Instance for Applicative by @ChristopherDavenport
• #2116 conversion PartialOrder to PartialOrdering and Hash to Hashing by @kailuowang
• #2100 Add comparison method in Order companion object by @ceedubs

Bug fixes:

• #2011 Rename ContravariantCartesian.scala to ContravariantSemigroupal.scala by @iravid
• #2016 Removed redundant Eq instance by @denisrosset
• #2029 make sure that EitherT MonadError syntax works the old way by @kailuowang

Documentation Improvements/Additions:

• #2007 move alleycats in readme by @kailuowang
• #2008 Upgrade Scalafix instructions by @gabro
• #2009 Correct it's -> its documentation errors by @kellen
• #2017 Fix alleycats module name by @benhutchison
• #2023 Fixes in Arrow docs by @Jasper-M
• #2026 Correctly close a tut:silent block in faq by @vendethiel
• #2027 Rename Validation to Validated in Validated docs by @Ttcao
• #2036 Clean up applicative syntax doc by @bkirwi
• #2035 Do not redirect to cats-mtl for MonadCombine by @vendethiel
• #2048 Add direct link to the scaladoc by @fagossa
• #2050 Link Directly to Cats Package in ScalaDoc by @stephen-lazaro
• #2031 Add parallel docs by @LukaJCB
• #2045 Fix scalafix testing instructions by @kubukoz
• #2068 Update symbols table by @stephen-lazaro
• #2070 Add some doctest examples for Alternative methods by @ceedubs
• #2065 added entry for sbt-catalysts by @kailuowang
• #2071 Add doc example for imap by @ceedubs
• #2073 Add doctests for Ior.fromOptions by @markus1189
• #2077 Add some doctest examples for SemigroupK/MonoidK by @ceedubs
• #2079 Add doctest examples for Applicative by @ceedubs
• #2095 Update guidelines.md by @kailuowang
• #2108 Update version of deprecation to 1.0.0-RC2 by @rossabaker

Build improvements/dependency updates

• #2028 Lawtesting: Update scalacheck-shapeless and cats by @vendethiel
• #2065 improve build by not displaying each success test by @kailuowang
• #2106 Update to latest patch versions of scala by @ceedubs
• #2114 sbt-coursier 1.0.0 by @sullis

Testing improvements

• #2037 Tests: MonadCombine->Alternative, add missing ones by @vendethiel
• #2052 Add labels to prop produced from IsEq by @nigredo-tori
• #2053 Fix #2051, Remove superfluous implicit by @rsoeldner
• #2081 Reduce redundancy in Semigroup and Eq test names by @ceedubs
• #2097 added distributeIdentityLaw by @kailuowang

Version 1.0.0-RC1

2017 Oct 21

This is the only planned release candidate release prior to 1.0.0.

Breaking changes and migration

• #1964 Require an Order instance for NonEmptyList's groupBy function by @igstan
• #1961 rename Cartesian to Semigroupal by @kailuowang
• #1955 Deprecate FlatMap's >> and << by @LukaJCB
• #1947 Rename EitherT.liftT to EitherT.liftF by @aeons
• #1934 Restruct functor by @kailuowang
• #1803 Convert ReaderWriterStateT to IndexedReaderWriterStateT by @iravid
• #1775 Convert StateT to IndexedStateT by @iravid
• #1098 Add a different MonoidK and SemigroupK instance for Kleisli by @peterneyens
• #1922 Make kernel laws consistent with core laws by @LukaJCB
• #1838 Sync NonEmptyList and NonEmptyVector methods by @durban
• #1914 Add Invariant instances for kernel type classes by @LukaJCB
• #1980 Make iterateRight in Foldable sound by @LukaJCB
• #1972 Add SortedMap and SortedSet instances/Move Set and Map instances to Alleycats by @LukaJCB/@kailuowang
• #1997 Minimizing typeclass surface in cats-kernel by @denisrosset
• #1987 Add mapK to transformers by @andyscott / @LukaJCB

To migrate from 1.0.0-MF.

• The rename of Cartesian to Semigroupal and EitherT.liftT to EitherT.liftF can be done automatically through Scalafix we provide. See instructions here.
• For FlatMap's >> and <<, use Apply's *> and <* instead.
• Profunctor and Strong were moved to the cats.arrow package, Bifunctor, Invariant and Contravariant were moved to the cats root package.
• SemigroupK[λ[α => Kleisli[F, α, α]]] and MonoidK[λ[α => Kleisli[F, α, α]]] are no longer implicitly available, Use Kleisli.endoSemigroupK and Kleisli.endoMonoidK to get them explicitly.
• law testing for type classes in cats.kernel was made consistent with the law testing in cats.core. Check here for a guide on how to test cats type class instances.
• NonEmptyList.concat that takes NonEmptlyList was deprecated, use NonEmptyList.concatNel instead.
• Monoid no longer has a InvariantMonoidal instance, we discovered that it's not lawful. It has have an Invariant and a Semigroupal (new name for Cartesian) instance.
• Foldable.iterateRight now takes an Iterable instead of Iterator, see #1973 for rationale.
• Foldable for Set and Traversable for Map were moved to Alleycats, see #1831 for rationale.
• cats.data.Kleisli#transform and cats.free.Coyoneda#transform were deprecated and replaced by mapK

New features / enhancements (API, instances, data types, etc.):

• #1958 Add FlatMap#flatTap, a more principled version of the kestrel combinator. by @hrhino
• #1950 more instances for Hash (#1712): Queue/Duration by @ctongfei
• #1942 add traverseN to cartesian syntax by @julien-truffaut
• #1939 Add guard to Alternative by @SystemFw
• #1933 Add syntax for ApplicativeError.fromEither by @tpolecat
• #1921 Optimize FreeApplicative.product by @peterneyens
• #1910 Add NonEmptyList.ofInitLast by @eddsteel
• #1888 Enhances stack safety for Eval. by @non
• #1885 Add zipWith to NonEmptyList and NonEmptyVector by @LukaJCB
• #1882 convert trait into abstract class for better bin compact by @kailuowang
• #1878 Add some instances we were missing. by @non
• #1858 Add NonEmptyList#partitionE by @LukaJCB
• #1847 Add right and left functor to BiFunctor by @LukaJCB
• #1840 Add Foldable and Traversable instances for Free by @aaronlevin
• #1819 Added more implementations of map2Eval in progress by @johnynek
• #1811 Move tuple Cartesian syntax implicit parameter by @DavidGregory084
• #1809 Add iterateWhileM and iterateUntilM by @drbild
• #1790 Implement EitherT#leftFlatMap and EitherT#leftSemiflatMap by @vendethiel
• #1784 Add existsM and forallM to Foldable by @refried
• #1712 Hash typeclass by @ctongfei
• #1976 Reduced usage of fold in Validated for better performance by @kailuowang
• #1967 Add a few type classes to generated tuple instances by @edmundnoble/@kailuowang
• #1984 Welcome, Alleycats by @kailuowang
• #1927 Add CommutativeApply and CommutativeApplicative by @LukaJCB
• #1837 Add Parallel type class by @LukaJCB
• #1998 Add Validated.cond and Validated.condNel by @andyscott

Bug fixes:

• #1917 Don't use package object convention for object source path by @travisbrown
• #1804 workaround for a possible scala bug in show for value class by @kailuowang
• #1980 Make iterateRight in Foldable sound by @LukaJCB

Documentation Improvements/Additions:

• #1970 Add docs for StateT and IndexedStateT by @iravid
• #1956 Mention the right issue number of doom. by @hrhino
• #1952 Added examples of Arrow composition by @raymondtay
• #1946 Give higher priority to partial-unification fix by @LukaJCB
• #1944 Fix typo. by @jooohn
• #1924 Add docs for Arrow by @zliu41
• #1923 Update footer by @kailuowang
• #1920 Document naming implicits according to @non s comment in #1061 by @tbje
• #1916 Fix tiny extra vowel typo by @andyscott
• #1915 Consolidate readme.md and index.md by @kailuowang
• #1913 updated footer by @kailuowang
• #1905 s/rewrites/rules and update scalafix version in the README by @gabro
• #1903 Validated beginners doc by @AlejandroME
• #1901 added FAQ item diff between cats and scalaz by @kailuowang
• #1900 add newts to related projects by @kailuowang
• #1899 Fix symbol signature for right and left apply in faq.md by @suhasgaddam
• #1897 add bin compat goal by @kailuowang
• #1895 trying to fix contributing page by @kailuowang
• #1894 Fix typo in background image of homepage. by @Ttcao
• #1890 Doc: Correct the URL of cats-mtl to the typelevel repository by @richardimaoka
• #1884 Rename typeclass => type class in Readme.md by @LukaJCB
• #1880 Add law testing guide by @LukaJCB
• #1875 Fix typo in SemigroupK scaladoc by @LukaJCB
• #1874 Fix typo in WriterT tests by @LukaJCB
• #1873 Add pureconfig and finch to ecosystem project list by @kailuowang
• #1872 Fix couple of typos in CHANGES.md by @LukaJCB
• #1871 Fix typo in Traverse#traverseWithIndexM by @LukaJCB
• #1857 Fix typo (Foldabale => Foldable) by @LukaJCB
• #1856 Remove mtl classes from menu by @LukaJCB
• #1854 Add EitherT docs by @Technius
• #1846 Add grafter to the list of Typelevel projects using cats by @etorreborre
• #1845 Adding the origami project to the list of Typelevel projects using cats by @etorreborre
• #1827 add trailing slashes to URLs by @larsrh
• #1822 Add docs for Ior by @LukaJCB
• #1820 Fix links by @n4to4
• #1817 Add seals to related projects by @durban
• #1816 Add Eval documentation by @LukaJCB
• #1814 remove outdated TODOs by @kailuowang
• #1808 minor link change by @kailuowang
• #1806 add notes to cartesian migration by @kailuowang
• #1799 add decline to project list by @kailuowang
• #1796 add Foldable.existsM/forallM to docs by @refried
• #1792 Add size control for typeclass diagram by @LukaJCB
• #1789 Add documentation for Show by @LukaJCB
• #1788 Add Eq docs by @LukaJCB
• #1787 Add NonEmptyTraverse docs by @LukaJCB
• #1781 promoting the ecosystem in readme a bit and fixed a typo by @kailuowang
• #1779 quick date fix by @kailuowang
• #1756 Add piecemeal import guide by @LukaJCB
• #1777 Add Reducible docs by @LukaJCB
• #1985 Links "LawTesting.md" in FAQ and TypeClasses pages by @AlejandroME
• #1993 Added examples for Cokleisli by @raymondtay

Build improvements/dependency updates

• #1948 Update scalafix project dependencies by @aeons
• #1926 Update coursier to version 1.0.0-RC12 by @mxl
• #1925 temporarily disable MiMa check on kernel by @kailuowang
• #1918 Update sbt-microsites to 0.7.0 by @LukaJCB
• #1902 Upgrade Scalafix to 0.5.0-RC2 by @gabro
• #1898 Update various sbt plugins by @fthomas
• #1892 Remove deprecated requiresDOM setting by @fthomas
• #1889 Add val for "compile-time" sbt Configuration by @fthomas
• #1887 Update sbt-pgp to 1.1.0 by @fthomas
• #1886 Update Scala.js to 0.6.20 by @fthomas
• #1876 build: use curly braces for disabling tasks by @fthomas
• #1868 Update sbt-microsites to 0.6.1 by @BennyHill
• #1866 Revert scalatest to 3.0.3 by @BennyHill
• #1865 Set simulacrum version to 0.11.0 by @BennyHill
• #1864 Set scalaz version to 7.2.15 by @BennyHill
• #1862 Bump kind-projector version to 0.9.4 by @shokohara
• #1861 Update sbt-scoverage to 1.5.1 by @fthomas
• #1860 Update sbt-pgp to 1.1.0-M1 by @LukaJCB
• #1859 Update sbt-sonatype by @LukaJCB
• #1852 Remove sbt-ghpages because it is pulled in by sbt-microsites by @fthomas
• #1849 Update sbt-git to 0.9.3 by @fthomas
• #1844 Replace botBuild with sbt-travisci's isTravisBuild by @fthomas
• #1843 Update sbt-unidoc to 0.4.1 by @fthomas
• #1842 Update partial-unification plugin to 1.1.0 by @fthomas
• #1839 Update scalastyle-sbt-plugin to 1.0.0 by @fthomas
• #1829 Update sbt-release to 1.0.6 by @fthomas
• #1828 Update sbt-jmh to 0.2.27 by @fthomas
• #1826 Pass sbt settings without varargs expansion by @fthomas
• #1825 Update sbt-coursier to 1.0.0-RC10 by @fthomas
• #1824 Update sbt-mima-plugin to 0.1.17 by @fthomas
• #1821 Update sbt-doctest to 0.7.0 by @fthomas
• #1795 Bump discipline version to 0.8 by @shokohara
• #1793 Add Scalafix rewrites for 1.0.0 by @gabro
• #1782 Bump scalacheck version to 1.13.5 by @shokohara
• #1780 Bump machinist version to 0.6.2 by @shokohara
• #1778 Bump sbt version to 0.13.16 by @shokohara

Testing improvements

• #1963 Move followedBy/forEffect tests to ApplyTests by @peterneyens
• #1960 Harmonize naming of discipline test classes in cats-kernel-laws. by @denisrosset
• #1953 Add a more direct tailRecM law. by @johnynek
• #1906 Fix Alternative law checking for IndexedStateT. by @iravid
• #1975 Unifies test naming standard. by @AlejandroME
• #1999 Fix order of comparison for EitherT.cond. by @andyscott

Scalafix for migration

• #1813 Add RenameInjectProdAndCoproduct, RenameTupleApplySyntax and RemoveSplit Scalafix rewrites by @gabro
• #1937 Add scalafix for contramap by @LukaJCB

Version 1.0.0-MF

2017 Aug 3

MF stands for milestone final. This is the last non-RC release before 1.0.0. The main purpose/focus of this release is to offer a relatively stable API to work with prior to 1.0.0. It can be deemed as a proposal for the final API we are going to maintain binary compatibility after 1.0. We will give community some time to validate it before we release 1.0.0-RC1.

To migrate from 0.9.0

We apologize for the number of breaking changes in this release. We are trying to include as many breaking changes as possible in this release before we lock down the API.

• cats no longer publishes the all-inclusive bundle package "org.typelevel" % "cats", use cats-core, cats-free, or cats-law accordingly instead. If you need cats.free, use "org.typelevel" % "cats-free", if you need cats-laws use "org.typelevel" % "cats-laws", if neither, use "org.typelevel" % "cats-core".
• cats.free.Inject is moved from cats-free to cats-core and renamed to cats.InjectK; cats.data.Prod is renamed to cats.data.Tuple2K; cats.data.Coproduct is renamed to cats.data.EitherK
• All Unapply enabled methods, e.g. sequenceU, traverseU, etc. are removed. Unapply enabled syntax ops are also removed. Please use the partial unification SI-2712 fix instead. The easiest way might be this sbt-plugin.
• FunctorFilter, MonadFilter, MonadReader, MonadState, MonadTrans, MonadWriter and TraverseFilter are no longer in cats, the functionalities they provided are inherited by the new cats-mtl project. Please check here for migration guide.
• MonadCombine is no longer in cats. Use Alternative or Monad + MonoidK instead.
• CartesianBuilder (i.e. |@|) syntax is deprecated, use the apply syntax on tuples instead. E.g. (x |@| y |@| z).map(...) should be replaced by (x, y, z).mapN(...). If you are getting "mapN not found" error message, it could be due to SI-2712, see the 3rd migration item above.
• Apply syntax on tuple (e.g. (x, y, z).map3(...)) was moved from cats.syntax.tuple._ to cats.syntax.apply._ and renamed to mapN, contramapN and imapN respectively.
• The creation methods (left, right, apply, pure, etc.) in EitherT were improved to take less type arguments.
• Several cats-core type class instances for cats.kernel were moved from their companion objects to separate traits and thus require imports from cats.instances.xxx._ (or the recommended import cats.implicits._) now. See #1659 for more details.
• Free.suspend is renamed to Free.defer for consistency.
• traverse1_, intercalate1 and sequence1_ in Reducible were renamed to nonEmptyTraverse_, nonEmptyIntercalate and nonEmptySequence_ respectively.
• foldLeftM is removed from Free, use foldM on Foldable instead, see #1117 for detail.
• iteratorFoldM was removed from Foldable due to #1716
• Split is removed, and the method split is moved to Arrow. Note that only under CommutativeArrow does it guarantee the non-interference between the effects. see #1567

If you feel adventurous you can try the experimental Scalafix rewrites. See all the available rewrites and the instructions here.

Breaking Changes:

• #1614: added leftT and improved existing lift API for EitherT. by @kailuowang
• #1596: Rename Inject to InjectK. by @andyscott
• #1589: Rename Prod, Coproduct to Tuple2K and EitherK. by @kailuowang
• #1583: Enable SI-2712 fix in cats / Remove unapply machinery. by @kailuowang
• #1679: remove Unapply class. by @kailuowang
• #1557: Improvements to Inject. @sellout
• #1659: move instances into separate trait. by @yilinwei
• #1709: Rename suspend to defer. by @peterneyens
• #1611: Renamed traverse1_, intercalate1 and sequence1_ in Reducible. by @LukaJCB
• #1117: foldLeftM without Free. by @TomasMikula
• #1487: Apply syntax for tuples. by @DavidGregory084
• #1745: Deprecate CartesianBuilder. by @kailuowang
• #1758: stop publishing cats all bundle , start to publish cats-testkit. by @kailuowang
• #1766: Replace Split with CommutativeArrow, introduces CommutativeMonad. by @diesalbla
• #1751: Removed FunctorFilter, MonadCombine, MonadFilter, MonadReader, MonadState, MonadTrans, MonadWriter, TraverseFilter. by @edmundnoble

New Features (API, instances, data types, etc):

• #1707: Add NEL/NEV one. by @peterneyens
• #1680: MonadTrans instance for RWST and make MonadTrans serializable. by @wedens
• #1658: Add Validated.validNel. by @edmundnoble
• #1651: Add state method to MonadState. by @oskoi
• #1628: add init and size methods to NonEmptyList. by @jtjeferreira
• #1612: Add ensureWith to Validated and Either (#1550). by @LukaJCB
• #1598: Implement a ReaderWriterStateT data type . by @iravid
• #1706: Clean up ReaderWriterStateT. by @peterneyens
• #1594: Add NonEmptyList#fromFoldable. by @markus1189
• #1611: Added NonEmptyTraverse. by @LukaJCB
• #1592: added instances of BitSet to allInstances. by @kailuowang
• #1586: Add Applicative.unit. by @alexandru
• #1584: Move arbitrary instance of StateT to laws. by @kailuowang
• #1580: add groupBy to NonEmptyList and groupByNel to List syntax @julien-truffaut
• #1578: add last, sortBy and sorted to NonEmptyList. by @julien-truffaut
• #1571: added whileM, untilM, iterateWhile, etc to Monad . by @tpolecat & @kailuowang
• #1548: MonadError instance for Ior. by @leandrob13
• #1543: MonadError instance for Kleisli. by @durban
• #1540: Ior syntax. by @leandrob13
• #1537: Add FlatMap.forEffect. by @cranst0n
• #1531: Add piecemeal import for MonadError. by @peterneyens
• #1526: Inject for free programs. by @tpolecat
• #1464: Adding get for Foldable. by @yilinwei
• #1602: Stack-safe Coyoneda. by @edmundnoble
• #1725: Add InjectK laws. by @andyscott
• #1728: Adds an As class which represents subtyping relationships (Liskov). by @stew
• #1178: Add Is constructor for Leibniz equality. by @tel
• #1611: Add NonEmptyTraverse typeclass. by @LukaJCB
• #1736: Added StackSafeMonad mixin. by @djspiewak
• #1600: Inject for Either. by @andyscott
• #1746: Add EitherNel type alias for Either[NonEmptyList[E], A]. by @andyscott
• #1670: Add Order-> Ordering implicit conversion to implicits, instances. by @edmundnoble
• #1649: Make Show inherit from a contravariant base trait for show string interpolator to be covariant. by @edmundnoble
• #1761: Add index related helpers to Traverse. by @andyscott
• #1769: Add Kleisli tap, tapWith. by @tpolecat
• #1739: Add onError and adaptError to ApplicativeError/MonadError. by @SystemFw
• #1644: Add MonadError instance for EitherT that recovers from F[_] errors. by @leandrob13
• #1748: Stack-safe FreeAppplicative. by @edmundnoble
• #1516: Implement NonEmptyList#Collect . by @xavier-fernandez

Code improvements:

• #1660: Override fromTry and fromEither for Try and Either. by @peterneyens
• #1642: Unseal InjectK to allow for extension by other libraries. by @andyscott
• #1641: Make InjectK use FunctionK.id for reflexive injection. by @andyscott
• #1618: Override some methods in Kleisli instances. by @peterneyens
• #1532: Override Foldable methods. by @peterneyens
• #1456: Consistency for ops classes. by @edmundnoble
• #1631: make all PartialApplied class value class to achieve zero cost. by @kailuowang
• #1696: Make syntax.show extend ShowSyntax instead of Show.ToShowOps. by @edmundnoble

Bug fixes:

• #1735: StateT no longer violates laws. by @djspiewak
• #1740: removed iteratorFoldM. by @kailuowang

Other miscellaneous improvements (documentation, tests, build):

• #1699: Link to sbt-partial-unification plugin . by @Blaisorblade
• #1698: Update gitter chat room name to cats-dev. . by @kailuowang
• #1695: update ETA for 1.0.0 . by @kailuowang
• #1604: Add tut doc for FunctionK . by @ceedubs
• #1691: Build JVM before JS on travis. by @peterneyens
• #1677: Update readme with the new dev channel.. by @kailuowang
• #1673: Use 2 workers in JVM build. by @ceedubs
• #1671: Fixing Eq[Function1] in testsJS; break JS build to separate matrix build. by @kailuowang
• #1666: Use Cogen for arbitrary instances. by @ceedubs
• #1654: Update Circe URL. by @n4to4
• #1653: Fix typo in FreeApplicative doc.. by @takayuky
• #1647: Adds Freestyle to Related Projects list. by @raulraja
• #1638: Make simulacrum a compile time only dependency. by @peterneyens
• #1637: show(f:T) to show(t:T). by @PeterPerhac
• #1636: added some category theory into FunctionK document. by @kailuowang
• #1632: upgraded to scala 2.12.2 and 2.11.11 and scalaJs. by @kailuowang
• #1629: add unit test for variance on methods in EitherT. by @jtjeferreira
• #1622: Update Discipline and ScalaTest. by @peterneyens
• #1615: Fix doc for InvariantMonoidal. by @BenFradet
• #1609: Include Id docs in the menu. by @ceedubs
• #1591: Improve test coverage. by @peterneyens
• #1590: Check monad laws for Cokleisli. by @peterneyens
• #1588: Docs/Tutorial -- Simplify Kleisli example. by @RawToast
• #1581: restore the alphabetical order of maintainers list. by @kailuowang
• #1575: minor improvements to tailRecM doc. by @kailuowang
• #1570: fixed a paragraph order. by @kailuowang
• #1566: Fix mistake in documentation of Group.remove. by @LukaJCB
• #1563: Remove references of the NEL OneAnd alias. by @peterneyens
• #1561: Fix incorrect numbering in FreeMonads doc. by @cb372
• #1555: fix scala.js badge version. by @xuwei-k
• #1551: added MonadError and ApplicativeError to hierarchy diagram. by @kailuowang
• #1547: fix ref to non-existent dir in contributing. by @sullivan-
• #1546: add to Monad ifM example. by @sullivan-
• #1545: fix scaladoc for Eval methods Unit, True, False, Zero, One. by @sullivan-
• #1541: Switch from CrossVersion.full to CrossVersion.patch for TLS compatibi…. by @milessabin
• #1530: add a favicon for sbt-microsite. by @larsrh
• #1529: Fix typo in Applicative doc.. by @cranst0n
• #1525: Remove link to apply.html from menu. by @Leammas
• #1693: Clean up EitherT doctests. by @peterneyens
• #1697: Added two links to the learner page. by @kailuowang
• #1726: Add underscore.io Advanced Scala with Cats. by @DieBauer
• #1718: Fixed some things in the build. by @djspiewak
• #1734: update sbt. by @jyane
• #1737: Rewrote documentation on the IO monad to reference cats-effect. by @djspiewak
• #1744: Make links link to the .html files instead of .md. by @LukaJCB
• #1759: Faster tests by reducing the size of lists. @peterneyens
• #1760: Decrease stack-safety test size. by @edmundnoble
• #1752: More coverage. by @edmundnoble
• #1472: Using regular syntax in the FreeApplicative tutorial. by @denisftw
• #1565: added instance table to docs, enhanced typeclass diagram. by @kailuowang
• #1573: Add symbols to FAQ. by @zainab-ali

Version 0.9.0

2017 January 15

The biggest user-facing change in this release is to the behavior of the flatMap (and related methods) provided by EitherOps for the standard library's Either for Scala 2.10 and 2.11. These methods now match the behavior of the flatMap on Either in Scala 2.12 in that they don't require the left-hand side types to match.

For example, the following would previously compile on 2.12, but not 2.10 or 2.11:

import cats.syntax.either._

sealed abstract class AppError
case object Error1 extends AppError
case object Error2 extends AppError

val either1: Either[Error1.type, String] = Right("hi")
val either2: Either[Error2.type, String] = Right("bye")

val result: Either[AppError, String] = for {
  v1 <- either1
  v2 <- either2
} yield v1 + v2

This code now works equivalently on all supported Scala versions.

Changes:

• #1424: NonEmptyList and NonEmptyVector are now covariant
• #1506: flatMap provided by Either syntax matches 2.12's Either#flatMap
• #1466: Improved stack safety for StateT
• #1510: catchNonFatal for Future is now asynchronous

Bug fixes:

• #1465 and #1507: Stack safety law for Monad#tailRecM is less eager and doesn't throw exceptions

New type class instances:

• #1475: Reducible instances for Eval and Id
• #1484: Show instance for Symbol

Other additions:

• #1446: Cofree comonad
• #1520 and #1522: intercalate for Foldable (and intercalate1 for Reducible)
• #1454: asLeft and asRight syntax methods for creating Either values
• #1468: tupleLeft and tupleRight for Functor
• #1500: putLeft, putRight, mergeLeft, and mergeRight methods for Ior
• #1495: show string interpolator
• #1448: Validated#findValid (like orElse but error accumulating)
• #1455: reverse for NonEmptyList
• #1517: zipWithIndex for NonEmptyList
• #1512 and #1514: filterNot for NonEmptyList and NonEmptyVector
• #1480: FunctionK#and
• #1481: EitherT.cond

Miscellaneous improvements (syntax, documentation, tests):

• #1513: Improved documentation for Functor, Applicative, and Traverse
• #1440: Improved type class documentation
• #1442: Improved documentation for Semigroup and Monoid
• #1479: Some instance traits are now package-private
• #1445: Workaround for Tut issue
• #1477: Use new kind-projector syntax for polymorphic lambdas
• #1483: Binary compatibility checking is now part of the build for cats-kernel
• #1469: More consistent instance names
• #1496: Simpler creation of some SemigroupK and MonoidK instances
• #1490: Avoid some duplication in build via sbt-travisci
• #1497: Site list clean-up

And version updates:

• #1499: 2.12 version is now 2.12.1
• #1509: Scala.js version is 0.6.14

As always thanks to everyone who filed issues, participated in the Cats Gitter channel, submitted code, or helped review pull requests.

Version 0.8.1

2016 November 9

Version 0.8.1 is a release to support Scala 2.12.0 with no changes to published code (only tests and documentation).

Build:

• #1457: Update to Scala 2.12.0

Miscellaneous improvements (syntax, documentation, tests):

• #1444: Remove defaultTailRecM from monad doc
• #1441: Fixes #1438 by replacing quoted entry name
• #1432: Type class organization in documentation
• #1439: Update version on index
• #1451: Fix Arbitrary instances for ScalaCheck 1.13.3+

Version 0.8.0

2016 October 25

Version 0.8.0 is the eighth Cats release, and the first release with support for Scala 2.12 (specifically the 2.12.0-RC2 release candidate).

Apart from the introduction of Scala 2.12 support, the biggest change in this release is the removal of Xor and XorT. See the FAQ for information about the motivations for this change and recommendations for migration.

Removals and deprecations:

• #1310: Xor and XorT are gone
• #1370: RecursiveTailRecM and Free#foldMapUnsafe are gone and stack safety is checked in the laws for Monad
• #1411: FreeT#interpret is deprecated in favor of the (equivalent) compile

Additions:

• #1382, #1415: Support for Scala 2.12.0-RC2
• #1414: Foldable#iteratorFoldM and lazy foldM implementations for many standard library instances
• #1356: append and prepend (and operator aliases) for NonEmptyVector
• #1327: EitherT.fromOption
• #1388: StateT.set and StateT.setF
• #1392: StateT.get
• #1325: WriterT.lift
• #1391: MonadReader#reader
• #1352: Macro-powered FunctionK.lift
• #1398: <<< and >>> aliases for Compose's compose and andThen
• #1408: toNestedValidated and toNestedValidatedNel for EitherT
• #1399: Order.fromComparable
• #1394: Traverse#flatSequence
• #1417: MonadTests#stackUnsafeMonad laws for instances where tailRecM is known to be unsafe
• #1411: compile and foldMap for the Free and FreeT companion objects

New instances:

• #1319: Order and Group for BigDecimal
• #1354: Semigroup for Ior
• #1395: Order for Symbol
• #1324: PartialOrder and other instances for BitSet
• #1324: Eq and PartialOrder for Either
• #1324: PartialOrder, Monoid, and other instances for Function0
• #1324: Monoid and other instances for Function1
• #1402: Monad, MonadCombine, Traverse, Order, etc. for Prod
• #1413: MonadError for StateT
• #1399: Instances for java.util.UUID

Renaming and rearrangements:

• #1385: The cats.js.std package is now cats.js.instances
• #1324: Many instances moved from cats-core to cats-kernel
• #1394: Traverse#traverseM is now flatTraverse

Miscellaneous improvements (syntax, documentation, tests):

• #1347: Consistency laws for combineAll and combineAllOption
• #1324: Performance improvements for Either instances
• #1386: FunctionK tests and examples now use kind-projector 0.9's polymorphic lambdas
• #1410: Replace Coproduct#run with Coproduct#fold
• #1331: Less expensive tailRecM-flatMap consistency checking
• #1330: More consistent parameter-less method definitions and usage, other syntactic improvements
• #1340: New Scaladex badge
• #1416: New diagram of type classes
• #1352: API docs for FunctionK
• #1369, #1418: New project site based on sbt-microsites
• #1259: 0.6-to-0.7 migration guide
• #1304, #1317, #1323, #1350, #1366, #1376, #1380, #1390, #1403, #1407, #1421: Other miscellaneous documentation improvements

Build:

• #1345: Update ScalaCheck (to 1.13.2) and Discipline (to 0.6)
• #1353: Generated sources are included in source jars
• #1322: Scala.js test clean-up
• #1426: Human-friendly names in metadata for published artifacts
• #1389: More memory for Travis CI

Version 0.7.2

2016 September 1

Version 0.7.2 is a patch release that was released to fix a major bug (#1346) that appeared in 0.7.0. It also contains several other improvements.

It should be safe to upgrade from 0.7.0 to 0.7.2 -- there are no major API changes between these releases.

Changes

Fixes:

• #1347: fixes broken Monoid[Map[K, V]].combineAll implementation.
• #1304: fix CoflatMap documentation.
• #1322: fix SBT commands (release, validate, etc.).
• #1311: rename some implicit instances for consistency.

Additions:

• #1319: add missing BigDecimal instances.
• #1324: add missing function and BitSet instances.

Note that 0.7.2 was preceded by a botched 0.7.1. release. Please avoid using this version of Cats -- it has major incompatibilities with 0.7.0 and is not documented here.

Version 0.7.0

2016 August 21

Version 0.7.0 is the seventh Cats release, and includes several major rearrangements and changes to names.

Migration notes

If you're updating from Cats 0.6.0, it's likely that you'll need to make extensive (but mostly mechanical) changes. The following list includes some of the changes that are likely to be necessary for most projects; see the complete list of changes below for more detail.

• All references to cats.std will need to be changed to cats.instances (#1140). If you're using cats.std.all or the other cats.std objects with wildcard imports, this is likely to be the only change you need to make. If you are importing or referring to instance definitions by name, you'll need to be aware that the naming convention has changed (see #1066, #1068, #1110, and #1122).
• NonEmptyList and NonEmptyVector are no longer type aliases for OneAnd, so any code using OneAnd to construct or pattern match on these types will need to be changed to use NonEmptyList or NonEmptyVector directly. There are also some API changes; for example, unwrap calls will need to be replaced by toList or toVector, and NonEmptyList(1, 2, 3) is now NonEmptyList.of(1, 2, 3).
• pureEval has been removed from Applicative (#1234), and has not been replaced, so if you are relying on it for laziness or effect capturing (which wasn't enforced or guaranteed), you'll need to find another approach.
• All references to NaturalTransformation will need to be replaced by either FunctionK or ~>.
• The FlatMap type class now has a tailRecM method that is designed to support stack-safe recursive monadic binding. If your monad's flatMap is stack safe, you can implement a stack-safe tailRecM by calling Monad#defaultTailRecM. The stack safety of tailRecM is not enforced, but if your implementation is stack safe, you should also provide an instance of the RecursiveTailRecM marker type class.
• If you are interpreting a free algebra into a context F with foldMap, you'll now need F to have an instance of the RecursiveTailRecM marker type class (in addition to the Monad instance).

If you run into any issues while updating, please get in touch on Gitter.

Changes

This release includes a fix for a bug in 0.6.0 (also fixed in 0.6.1):

• #1062: Order instances for tuples are now lexicographic (instead of only comparing first elements)

And other bug fixes:

• #1096: inj and prj on Inject now work consistently with respect to null

And some additions:

• #1289 and #1306: EitherT and improved Either syntax
• #1280: FlatMap now has a tailRecM method
• #1280: RecursiveTailRecM marker type class indicating that tailRecM is stack safe
• #1266: FreeT monad transformer
• #1225: FunctorFilter and TraverseFilter
• #1121: valueOr and merge for Validated
• #1188: toValidatedNel for XorT
• #1127: toTry for Xor
• #1269: catchNonFatal for ApplicativeError
• #1130: isEmpty syntax method for Monoid
• #1167: minimum, maximum, and related helper methods for Foldable and Reducible
• #1243: distinct on NonEmptyList and NonEmptyVector
• #1134: cats.syntax.list for à la carte list syntax imports
• #1191: cats.syntax.monoid for à la carte Monoid syntax imports
• #588 and #1063: IdT, the identity monad transformer
• #1021 and #1221: Nested (represents nested composition of type constructors)
• #1172: toNested for OptionT and XorT
• #1102 and #1170: Comparison (represents the result of an Order comparison)
• #1090: Kleisli.lift
• #1169: lift, inspect, and related methods for StateT
• #1114: size for Foldable
• #1193: reduceLeftM for Reducible
• #1097: Functor variance helpers (widen for Functor and narrow for Contravariant)
• #1207: tell for Writer and WriterT, value for Writer
• #1155: Convenience methods for constructing XorT values
• #1085: runTailRec and foldLeftM for Free
• #1299: ContravariantCartesian type class

And some name changes:

• #1140: cats.std is now cats.instances
• #1066, #1068, #1110, and #1122: More unique type class instance names
• #1072: NaturalTransformation is now FunctionK
• #1085: mapSuspension on Free is now compile
• #1111: Free.Gosub is now Free.FlatMapped
• #1133: Composite* traits for binary type classes are renamed to Composed* for consistency (and are now private)

And other API changes:

• #1231: NonEmptyList is now a case class instead of a type alias for a OneAnd
• #1137: NonEmptyVector is now a value class instead of a type alias for a OneAnd
• #1267: Overloaded variadic apply on NonEmptyList and NonEmptyVector is now of
• #1234: Applicative#pureEval has been removed
• #1202: MonadFilter no longer has a filterM method (see #1225)
• #1075: foldMap on Free now requires a MonadRec instance (instead of simply Monad)
• #1085: Free.suspend no longer requires an Applicative instance
• #1084: Safer toString for Free and FreeApplicative
• #1100: Simplified constraints for methods on Xor and related types
• #1171: Prioritization traits are now private

And many new instances:

• #1059 and #1147: Monoid, MonadError, and other instances for scala.util.Try
• #1299: Monad for Tuple2
• #1211: Contravariant for Eq
• #1220: Traverse and Comonad for Tuple2
• #1103: Order, MonadError, and other instances for OptionT
• #1106: Semigroup and Monoid for XorT
• #1138: SemigroupK and MonadCombine for StateT
• #1128 Semigroup and Monoid for Applicative
• #1049: CoflatMap for WriterT
• #1076 and #1261: MonadRec instances for Eval, StateT, and Future
• #1105: Unapply instances for Nested shapes

And miscellaneous improvements to style and performance:

• #1079: More consistent type lambdas
• #1300: Much faster Monoid instances for Map

And improvements to the documentation:

• #1145: Major rearrangements and additions
• #1136: New chart for symbols
• #1052: New "Why?" section
• #1095, #1226, and #1227: New FAQ section
• #1163: New import guide section
• #1217, #1223, and #1239: New related projects
• #1057 and #1157: Copy-paste-friendly code blocks
• #1104 and #1115: Kitchen-sink imports in example code
• #1050: Switch to rouge for syntax highlighting in the GitHub Pages site
• #1119: Fix for contramap signature
• #1141 and #1162: Fixes for cats-kernel documentation
• #1149: Spelling consistency for "type class"
• #1183: More documentation about use of Machinist, Simulacrum, and kind-projector
• #1056: Clarification about forgetful functors and the free monad
• #1131 and #1241: Simplified project structure listings
• #1185, #1186, and #1189: Miscellaneous improvements for Traverse documentation

And the build:

• #1159: Binary compatibility checking for cats-kernel via MiMa
• #1256: More reliable Scala.js testing in Travis CI
• #1123: cats-kernel is now included in the API documentation
• #1051: Empty Scaladocs for 2.10 to avoid issues macros cause for API documentation generation on 2.10
• #1154: Better POM hygiene: no Scoverage dependency
• #1153 and #1218: More consistent use of Simulacrum for syntax
• #1093: Scalastyle is now aware of shared and Scala.js-specific source files
• #1142: Additional formatting rules for Scalastyle
• #1099: Type lambda style is now enforced by Scalastyle
• #1258: Version updates for SBT and SBT plugins

We also welcome Kailuo Wang, Peter Neyens, and Oscar Boykin as new Cats maintainers!

Version 0.6.1

2016 July 14

Version 0.6.1 is a patch release compatible with 0.6.0.

It contains one bug fix:

• #1062: Fixed a bug in the Order and PartialOrder instances for Tuple2+ where only the first element was used in comparisons

It also contains a change to the build:

• #1173: Add binary compatibility check to all published modules

Version 0.6.0

2016 May 19

Version 0.6.0 is the sixth release.

Highlights of this release:

• #990: Separate free package into its own module
• #1001: Introduce cats-kernel and remove algebra dependency

This release also includes some API changes:

• #1046: summon ApplicativeErrorSyntax for F[_] instead of F[_, _]
• #1034: Don't combine lefts on Xor and XorT combine
• #1018: Remove blocking (JVM-only) Future instances
• #877: Remove required laziness in Prod, fixes #615

And additions:

• #1032: Added Coproduct fold
• #1028: Added withFilter for OptionT
• #1014: Added Monoid instance for WriterT
• #1029: Added an ApplicativeError instance for Kleisli and a MonadError[Option, Unit] to std.option
• #1023: Add XorT#fromEither
• #984: Add Validated.ensure
• #1020: Add Traverse.traverseM

And some code improvements:

• #1015: Add Apply.map2Eval and allow traverse laziness
• #1024: Override reverse on reversed PartialOrder to return original instance
• #880: Optimize Eq[Vector[A]] instance
• #1019: Use Future#successful in pureEval when possible

And bug fixes:

• #1011: Add missing type parameters.

And some other improvements to the organization documentation, tutorials, laws and tests, including:

• #1045: Add a link to the OptionT documentation from the monad docs.
• #1043: Add notes about kind-projector usage in docs
• #1042: Cats 0.5.0 no longer pre-release
• #1036: Add FPiS to the "Resources for Learners" section
• #1035: Run kernel-law tests for JS as part of build
• #991: Replace ~> with NaturalTransformation
• #1027: Remove unnecessary nelSemigroup from traverse doc
• #1022: Add law-checking for asMeetPartialOrder and asJoinPartialOrder
• #990: Separate free package into its own module

Version 0.5.0

2016 April 28

Version 0.5.0 is the fifth release.

This release includes some API changes:

cats.laws.discipline.eq no longer provides Eq instances for Tuple2 and Tuple3, these instances and together with some other new instances for Tuples are now provided by cats.std.tuple (through inheriting the instance trait defined in algebra 0.4.2).

• #910: Remove Streaming and StreamingT
• #967: product and map can be implemented in terms of ap
• #970: Renamed Kleisli#applyto ap
• #994: updated to latest algebra (brought in all the new goodies)

And additions:

• #853: Adds a new LiftTrans type class
• #864: Add Bifoldable
• #875: Add .get method to StateT
• #884: Add Applicative syntax
• #886: Add map method to OneAnd
• #927: XorT.ensure method
• #925: Stack-safe foldM
• #922: Add tell and writer syntax for creating Writers.
• #903: Add Bitraverse
• #928: Add missing Show instances
• #940: More flexible TransLift
• #946: Added OptionT.none
• #947: Syntax for ApplicativeError
• #971: Add toValidatedNel to Xor
• #973: Add flatMapF for StateT
• #985: Add object reducible for reducible syntax
• #996: Add SemigroupK instance for Xor
• #998: Add SemigroupK instance for Validated
• #986: Add Bitraverse instances for Validated and XorT

And bug fixes:

• #873: Fix OptionIdOps.some to always return Some
• #958: Switch off scaladoc generation for Scala 2.10 due to macro problems
• #955: Rename Id instances to idInstances to make selective import easier

And removals:

• #910: Remove Streaming and StreamingT

And some other improvements to the documentation, tutorials, laws and tests, including:

• #880: Optimize Eq[Vector[A]] instance
• #878: Fix bug in freemonad doc
• #870: Fixed doc string for StateT's runEmptyA()
• #866: Add some tests for Coproduct and WriterT
• #883: Delegate to Traverse.sequence in Applicative.sequence
• #893: Add Reducible laws
• #923: Make Call.loop @tailrec optimized
• #916: add -P:scalajs:mapSourceURI option
• #909: Make Bifunctor universal
• #905: make Unapply serializable
• #902: Make table in Kleisli readable
• #897: Add Prod tests
• #938: Onward to scala 2.11.8
• #941: Type class composition and MonadState tests
• #949: Add .ensime_cache to gitignore
• #954: Switch to use nodeJsEnv as default jsEnv to build scala.js
• #956: Upgrade scala.js from 0.6.7 -> 0.6.8
• #960: More Reducible tests
• #962: Improving test coverage
• #964: Clarify stabilty guarantees; drop 'proof of concept' and 'experimental'
• #972: Fix swapped f and g in invariant docs
• #979: Fix outdated import for cats.syntax.apply._
• #995: Move coverage away from bash
• #1002: Correct the URL for Data types à la carte
• #1005: fix broken link in foldable docs

As always thanks to everyone who filed issues, participated in the Cats Gitter channel, submitted code, or helped review pull requests.

Version 0.4.1

2016 February 4

Version 0.4.1 is a patch release in the 0.4 series and is binary compatible with version 0.4.0.

This patch fixes bugs with the dropWhile methods on Streaming and StreamingT.

This release corrects outdated build/POM metadata, which should fix API doc URLS.

Bug fixes:

• #856: Fix Streaming and StreamingT dropWhile functions

Build/publishing changes:

• #852 Update build with org change

Documentation and site improvements:

• #859 Add Contravariant documentation page
• #861 Docs: Revive useful links section. Update URLs

Version 0.4.0

2016 February 1

Version 0.4.0 is the fourth release of the Cats library, and the first release published under the org.typelevel group from the Typelevel organization on GitHub (previous releases had been published to org.spire-math from non/cats). This means that users will need to change the groupId for their Cats dependencies when updating. If you have a line like this in your sbt build configuration, for example:

libraryDependencies += "org.spire-math" %% "cats" % "0.3.0"

You will need to change it to the following:

libraryDependencies += "org.typelevel" %% "cats" % "0.4.0"

This release no longer includes cats-state or cats-free artifacts, since the cats.state and cats.free packages have been moved into cats-core.

If you've checked out the GitHub repository locally, it would be a good idea to update your remote to point to the new organization, which will typically look like this (note that you should confirm that origin is the appropriate remote name):

git remote set-url origin git@github.com:typelevel/cats.git

This release includes a large number of breaking changes, including most prominently the introduction of a new Cartesian type class that is a supertype of Monad (and many other types). If you use the |@| syntax that had previously been provided by Apply, you'll need to change your imports from cats.syntax.apply._ to cats.syntax.cartesian._. For example:

scala> import cats.Eval, cats.syntax.cartesian._
import cats.Eval
import cats.syntax.cartesian._

scala> (Eval.now("v") |@| Eval.now(0.4)).tupled
res0: cats.Eval[(String, Double)] = cats.Eval$$anon$5@104f8bbd

Other changes in this release are described below.

This version includes API changes:

• #555: |@| syntax is now provided by cats.syntax.cartesian
• #835: State and StateT are now in the cats.data package
• #781: combine on SemigroupK is now combineK
• #821 and #833: The order of arguments for ap has been reversed (now function first)
• #833: ap on CartesianBuilderN is now apWith
• #782: State now uses Eval instead of Trampoline for stack safety
• #697: or for natural transformations is now an instance method
• #725: orElse on XorT and does not unnecessarily constrain the type of the left side of the result
• #648: Some types now extend Product and Serializable to improve type inference
• #647: ProdInstancesN names changed for consistency
• #636: Eval is now Serializable
• #685: Fixes for copy-paste errors in method names for instances for Validated
• #778: Unnecessary type parameter on Foldable's sequence_ has been removed

And additions:

• #555 and #795: Cartesian
• #671: Coproduct and Inject
• #812: ApplicativeError
• #765: State and Free (and related types) are now in the core module
• #611: Validated now has an andThen method that provides binding (but without the for-comprehension syntactic sugar that the name flatMap would bring)
• #796: sequenceU_ and traverseU_ on Foldable
• #780: transformS for StateT
• #807: valueOr for XorT
• #714: orElse for XorT
• #705: getOrElseF for XorT
• #731: swap for Validated
• #571: transform and subflatMap on OptionT and XorT
• #757 and #843: compose for Alternative and composeK for MonoidK
• #667: OptionT.liftF

And removals:

• #613: Free and FreeApplicative constructors are now private
• #605: filter on Validated
• #698: MonadCombine instances for OptionT
• #635: Kleisli's redundant lmap, which was equivalent to local
• #752: Cokleisli.cokleisli, which was equivalent to Cokleisli.apply
• #687: Unused XorTMonadCombine
• #622: Many prioritization types are now private

And new type class instances:

• #644: Traverse and Foldable instances for XorT
• #691: Various instances for Function1
• #628 and #696: Various instances for WriterT
• #673: Bifunctor instances for WriterT
• #715 and #716: Semigroup and Monoid instances for Validated
• #717 and #718: Semigroup instances for Xor and Const
• #818: CoflatMap instance for Vector
• #626: Contravariant instances for Const and Kleisli
• #621: Id instances for Kleisli
• #772: Reducible instances for OneAnd
• #816: Traverse instances for OneAnd
• #639: Traverse instance for Id
• #774 and #775: Show instances for Vector and Stream

And bug fixes:

• #623 fixes #563, a bug in the behavior of dropWhile_ on Foldable
• #665 fixes #662, a bug that resulted in re-evaluation after memoization in Streaming
• #683 fixes #677, a bug in Streaming.thunk
• #801: Fixes order effect bug in foldMap on FreeApplicative
• #798: Fixes bug in filter on StreamingT
• #656: Fixes bug in drop on StreamingT
• #769: Improved stack consumption for Eval.Call

And some dependency updates:

• #833: Update to Simulacrum 0.7.0
• #764: 2.10 version is now 2.10.6
• #643: Update to Catalysts 0.2.0
• #727: Update to Scalastyle 0.8.0

There are also many improvements to the documentation, tutorials, laws, tests, and benchmarks, including the following:

• #724: sbt-doctest is now used to validate Scaladoc examples
• #806: Various improvements to use of Simulacrum, which is now a compile-time-only dependency
• #734: Documentation on testing conventions
• #710: Documentation for Invariant
• #832: Updated Free documentation
• #824: New examples for Foldable
• #797: Scaladoc examples for methods on Arrow
• #783 and others: Scaladoc examples for syntax methods
• #720: Expanded documentation for FreeApplicative
• #636: Law checking for Eval
• #649 and #660: Better Arbitrary instances for Streaming and StreamingT
• #722: More consistent toString for StreamingT
• #672: Additional laws for Profunctor
• #668, #669, #679, #680, and #681: Additional law checking for Xor, XorT, and Either
• #707: Additional testing for State and StateT
• #736: map / flatMap coherence
• #748: Left and right identity laws for Kleisli
• #753: Consistency tests for Cokleisli
• #733: Associativity laws for Kleisli and Cokleisli composition
• #741: Tests for Unapply-supported syntax
• #690: Error reporting improvements for serializability tests
• #701: Better documentation for the Travis CI script
• #787: Support for cross-module Scaladoc links

Known issues:

• #702: This change identified and fixed a stack safety bug in foldMap on Free, but raised other issues (see #712) and was reverted in #713; #721 now tracks the non-stack safety of Free's foldMap

As always thanks to everyone who filed issues, participated in the Cats Gitter channel, submitted code, or helped review pull requests.

Version 0.3.0

2015 November 8

Version 0.3.0 is the third release of the Cats library.

This version includes new type class instances:

• #545: Semigroup instances for OneAnd
• #521: Monoid instances for Xor when the left side has a Semigroup instance and the right side has a Monoid
• #497: Monoid instances for Set
• #559: Bifunctor instances for Validated, Ior, Xor, and XorT
• #569: Functor instances for OptionT when F has a Functor instance but not a Monad
• #600: Show instances for Option and OptionT
• #601: Show instances for List
• #602: Show instances for Set
• #568: Several new Unapply shapes

And API changes:

• #592: fromTryCatch on Xor and Validated is now catchOnly
• #553: MonadError now characterizes type constructors of kind * -> * instead of (*, *) -> *
• #598: OneAnd's type constructor type parameter is now before the element type
• #610: XorT's toOption returns an OptionT[F, B] instead of an F[Option[B]]
• #518: Free's resume method now returns an Xor instead of an Either
• #575 and #606: orElse on Xor and Validated does not unnecessarily constrain the type of the left side of the result
• #577: *Aux helper classes have been renamed *PartiallyApplied

And additions:

• #542: WriterT
• #567: Ior.fromOptions
• #528: OptionT.fromOption
• #562: handleErrorWith and related helper methods on MonadError
• #520: toNel and fromList conversions from List to NonEmptyList
• #533: Conversions between types with Foldable instances and Streaming
• #507: isJvm and isJs macros in the new cats.macros.Platform
• #572: analyze on FreeApplicative for compilation into a Monoid
• #587: Syntax for lifting values (and optional values) into Validated

And several aliases:

• #492: FlatMapSyntax now includes followedBy, which is an alias for >>, together with a new followedByEval, which allows the caller to choose the evaluation strategy of the second action
• #523: Foldable now has a combineAll method that aliases fold and allows postfix usage via FoldableSyntax

And a few removals:

• #524: FreeApplicative's redundant hoist, which was equivalent to compile
• #531: Coyoneda's by
• #612: Many prioritization and instance traits are now private

And bug fixes:

• #547: The empty values for Monoid[Double] and Monoid[Float] are now 0 instead of 1
• #530: Streaming.take(n).toList no longer evaluates the n + 1-st element
• #538: OneAnd's instances are properly prioritized

There are also many improvements to the documentation, tutorials, laws, tests, and benchmarks:

• #522: ScalaTest's === now uses Eq instances
• #502: Traverse's laws verify the consistency of foldMap and traverse
• #519: Benchmarks (and performance improvements) for Eval
• …and many others

Thanks to everyone who filed issues, participated in the Cats Gitter channel, submitted code, or helped review pull requests.

Version 0.2.0

2015 August 31

Version 0.2.0 is the second release of the Cats library.

The most exciting feature of this release is Scala.js support, which comes courtesy of much hard work by the Scala.js community (especially Alistair Johnson). The sbt build configuration and project layout were updated to support building for both the JVM and JS platforms.

Since the 0.1.2 release there was wide agreement that the split between cats-core and cats-std was awkward. The two projects have been combined into cats-core, meaning that type class instances for common types like List are now available in cats-core.

There was also a concerted effort to improve and add documentation to the project. Many people helped find typos, broken links, and places where the docs could be improved. In particular, the following tutorials were added or overhauled:

• Applicative
• Const
• Foldable
• Free
• FreeApplicative
• Kleisli
• Monad
• Monoid
• Semigroup
• SemigroupK
• Traverse
• Validated
• Xor

Several new type classes and data types were introduced:

• Choice[F[_, _]]
• Group[A]
• MonadReader[F[_, _], R]
• Streaming[A] and StreamingT[F[_], A]
• Prod[F[_], G[_], A] and Func[F[_], A, B]

Syntax tests were added to ensure that existing syntax worked, and there has been some movement to enrich existing types with syntax to make converting them to Cats types easier.

The previous Fold[A] type, which was used to support lazy folds, has been replaced with Eval[A]. This type supports both strict and lazy evaluation, supports lazy map and flatMap, and is trampolined for stack safety. The definition of Foldable#foldRight has been updated to something much more idiomatic and easier to reason about. The goal is to support laziness in Cats via the Eval[A] type wherever possible.

In addition to these specific changes there were numerous small bug fixes, additions, improvements, and updates. Thanks to everyone who filed issues, participated in the Cats Gitter channel, submitted code, or helped review pull requests.

Version 0.1.2

2015 July 17

(Due to problems with publishing 0.1.0 and 0.1.1 are incomplete.)

Version 0.1.2 is the first non-snapshot version of the Cats library! It is intended to assist the creation of dependent libraries and to be an early look at Cats' design.

Much of the library is quite mature, but there are no source- or binary-compatibility guarantees at this time. The overarching design of the library is still somewhat in flux, although mostly we expect there will be new type classes, instances, and syntax. Some package and module boundaries may also shift.

For complete credits, see AUTHORS.md for a list of people whose work has made this release possible.