ghc-microlens

NOTE: If you're writing an app, you probably want
<http://hackage.haskell.org/package/microlens-platform microlens-platform> – it
has the most features. <http://hackage.haskell.org/package/microlens 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 <http://hackage.haskell.org/package/lens 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 <https://github.com/stevenfontanella/microlens#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
<http://hackage.haskell.org/package/ilist ilist> provides indexed functions for
lists).

You want a library with a clean, understandable implementation (in which case

you're looking for <http://hackage.haskell.org/package/lens-simple
lens-simple>).
As already mentioned, if you're writing an application which uses lenses more
extensively, look at <http://hackage.haskell.org/package/microlens-platform
microlens-platform> – it combines features of most other microlens packages
(<http://hackage.haskell.org/package/microlens-mtl microlens-mtl>,
<http://hackage.haskell.org/package/microlens-th microlens-th>,
<http://hackage.haskell.org/package/microlens-ghc microlens-ghc>).
If you want to export getters or folds and don't mind the
<http://hackage.haskell.org/package/contravariant contravariant> dependency,
please consider using <http://hackage.haskell.org/package/microlens-contra
microlens-contra>.
If you haven't ever used lenses before, read
<http://hackage.haskell.org/package/lens-tutorial/docs/Control-Lens-Tutorial.html
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.

          

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License: BSD-3-Clause
URL: https://hackage.haskell.org/package/microlens