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 Isos, Prisms, 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.