Announcement: cats 1.0.0-MF

by Kailuo Wang on Aug 04, 2017


The cats maintainer team is proud to announce the cats 1.0.0-MF release.

MF stands for milestone final, this will be the last release before cats 1.0.0-RC1 which will be followed by cats 1.0 shortly.

The main purpose/focus of this release is to offer a relatively stable API to work with prior to the official 1.0. It can be deemed as a proposal for the final cats 1.0 API. Please help test it and report any improvements/fixes needed either in the cats-dev gitter channel or as github issues. Post cats 1.0, we will keep API stable and maintain strong binary compatibility.

Highlights of the major new features include but not limited to:

  • #1117: Stack safe foldLeftM without Free, by @TomasMikula
  • #1598: A ReaderWriterStateT data type, by @iravid
  • #1526 and #1596: InjectK for free programs, by @tpolecat and @andyscott
  • #1602: Stack-safe Coyoneda, by @edmundnoble
  • #1728: As class which represents subtyping relationships (Liskov), by @stew
  • #1178: Is constructor for Leibniz equality, by @tel
  • #1748: Stack-safe FreeApplicative, by @edmundnoble
  • #1611: NonEmptyTraverse. by @LukaJCB

Overall 1.0.0-MF has over 120 merged pull requests of API additions, bug fixes, documentation and misc improvements from 44 contributors. For the complete change list please go to the release notes.


There are more breaking changes in this release - we want to include as many necessary breaking changes as possible in this release to reach stability. Please follow the migration guide from 0.9.0 in the release notes.

What’s next

Although we made many improvements to the documentation in this release, it’s still by and large a WIP. The next release 1.0.0-RC1 will focus documentation and API refinement based on community feedback. RC1 is scheduled to be released in September. Unless the amount of bug fixes warrants a RC2, it’s likely that we’ll release cats 1.0.0 within a couple weeks after RC1.


Last but not least, many thanks to the contributors that make this release possible:

  • @alexandru
  • @andyscott
  • @BenFradet
  • @Blaisorblade
  • @cb372
  • @ceedubs
  • @cranst0n
  • @DavidGregory084
  • @denisftw
  • @DieBauer
  • @diesalbla
  • @djspiewak
  • @durban
  • @edmundnoble
  • @iravid
  • @jtjeferreira
  • @julien-truffaut
  • @jyane
  • @kailuowang
  • @larsrh
  • @Leammas
  • @leandrob13
  • @LukaJCB
  • @markus1189
  • @milessabin
  • @n4to4
  • @oskoi
  • @peterneyens
  • @PeterPerhac
  • @raulraja
  • @RawToast
  • @sellout
  • @stew
  • @sullivan-
  • @SystemFw
  • @takayuky
  • @tel
  • @TomasMikula
  • @tpolecat
  • @wedens
  • @xavier-fernandez
  • @xuwei-k
  • @yilinwei
  • @zainab-ali