microlens support for Reader/Writer/State from mtl


Version on this page:
LTS Haskell 22.23:
Stackage Nightly 2024-05-27:
Latest on Hackage:

See all snapshots microlens-mtl appears in

BSD-3-Clause licensed by Edward Kmett, Artyom Kazak
Maintained by Monadfix
This version can be pinned in stack with:microlens-mtl-,1777

Module documentation for

This package contains functions (like view or +=) which work on MonadReader, MonadWriter, and MonadState from the mtl package.

This package is a part of the microlens family; see the readme on Github.


  • No more conditional Safe (see #122).


  • Removed of equality constraints on Zoom and Magnify, as was done in lens earlier. This allows instances of Zoom and Magnify for FreeT. (Thanks to @treeowl.)

  • Fixed compilation on GHC 8.4.

  • Exported Focusing, etc. from Lens.Micro.Mtl.Internal.
  • Added &~.

  • Added <?= and <.=.

  • Added ?= and <~.

  • Added assign and modifying as synonyms for .= and %=.
  • Added <%=, <<%=, and <<.=.

  • Added forgotten copyright/authorship information.

  • Added preuse.

  • Bumped transformers version.
  • Bumped microlens version.

  • Added Lens.Micro.Mtl.Internal (which exports zooming type classes)

  • Added Safe Haskell pragmas.

  • Bumped microlens version.

  • Added preview (a synonym for (^?)).
  • Bumped microlens version.

  • Bumped microlens version.

  • Moved some internally used functions to Lens.Micro.Internal in microlens.
  • Bumped base version.

  • Package now compiles with -O2 and other optimisations by default.

  • Added zoom and magnify.

Initial release.