A tiny lens library with no dependencies. If you're writing an app, you probably want microlens-platform, not this.
|Version on this page:||0.4.7.0|
|LTS Haskell 19.8:||0.4.12.0|
|Stackage Nightly 2022-05-25:||0.4.12.0|
|Latest on Hackage:||0.4.13.0|
NOTE: If you're writing an app, you probably want microlens-platform – it has the most features. microlens is intended more for library writers who want a tiny lens library (after all, lenses are pretty useful for everything, not just for updating records!).
This library is an extract from lens (with no dependencies). It's not a toy lenses library, unsuitable for “real world”, but merely a small one. It is compatible with lens, and should have same performance. It also has better documentation.
There's a longer readme on Github. It has a migration guide for lens users, a description of other packages in the family, a discussion of other lens libraries you could use instead, and so on.
Here are some usecases for this library:
You want to define lenses or traversals in your own library, but don't want to depend on lens. Having lenses available often make working with a library more pleasant.
You just want to be able to use lenses to transform data (or even just use
over _1to change the first element of a tuple).
You are new to lenses and want a small library to play with.
However, don't use this library if:
Prisms, indexed traversals, or actually anything else which isn't defined here (tho some indexed functions are available elsewhere – containers and vector provide them for their types, and ilist provides indexed functions for lists).
You want a library with a clean, understandable implementation (in which case you're looking for lens-simple).
As already mentioned, if you're writing an application which uses lenses more extensively, look at microlens-platform – it combines features of most other microlens packages (microlens-mtl, microlens-th, microlens-ghc).
If you haven't ever used lenses before, read this tutorial. (It's for lens, but it applies to microlens just as well.)
Note that microlens has no dependencies starting from GHC 7.10 (base-4.8). Prior to that, it depends on transformers-0.2 or above.
- Fixed the Haddock crash on GHC 8 by removing default method implementations (
each = traverseand
ix = ixAt). If you had custom instances of
Eachwhich relied on default methods, they’d stop working.
- Changed fixities of
.#to the ones in the profunctors package. Those operators are only available from
Lens.Micro.Internal, so this shouldn’t affect most users.
<&>(which makes lens creation easier).
- Fixed markup in the .cabal file.
- Added descriptions of other packages to
- More changes to make microlens-platform more prominent.
- Pointed to microlens-platform in the synopsis.
- Added forgotten copyright/authorship information.
- Fixed a bug that wasn’t letting the package compile with GHC 8.0 (see issue #63).
SimpleFoldand put them into
Foldare available in microlens-contra.
Applicative (Const r)constraints with
Monoid rbecause it’s the same thing but easier to understand.
- Backported the fix for the bug that wasn’t letting the package compile with GHC 8.0 (see issue #63).
Fold. Now you no longer need microlens-mtl if the only thing you need from it is
- Changed the description of the package from “A tiny part of the lens library which you can depend upon” to “A tiny part of the lens library with no dependencies” because the previous one was ambiguous (I admit I kinda liked that ambiguity, tho).
- Added Safe Haskell pragmas.
- Moved some things into
- Bumped base version.
- Moved some things into
Field*aren’t exported by
ASetter', which is useful because we can’t provide real