microlens-0.4.13.1: A tiny lens library with no dependencies

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 _1 to 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:

• You need Iso s, Prism s, indexed traversals, or actually anything else which isn't defined here (though 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 want to export getters or folds and don't mind the contravariant dependency, please consider using microlens-contra .

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.