haskell@gentoo.org
Gentoo Haskell
This module, <http://hackage.haskell.org/package/lens-simple/docs/Lens-Simple.html Lens.Simple>,
just re-exports the main modules from Russell O\'Connor's
<http://hackage.haskell.org/package/lens-family lens-family> package, the
original van Laarhoven-O'Connor lens library.
@lens-family@ is particularly remarkable for its minute number of dependencies:
(apart from <http://hackage.haskell.org/package/mtl mtl>
they are all ghc \'boot\' libraries); but more importantly for its
extreme conceptual simplicity and theoretical soundness. Much of
the material it contains is well-explained, from a tutorial point of view, by
<http://hackage.haskell.org/package/lens-tutorial lens-tutorial> It is independent,
self-standing and readily intelligible apart from any darker
more general system of combinators that might attempt to extend it. Much
of it ought to be in the Prelude.
Convenient import of the elementary combinators from @lens-family@,
however, a little complicated. The idea of this trivial module, then, is just to make a sort of
low-powered, minimal-dependency, @lens-family@ equivalent of
the 800 lb gorilla of lens library imports:
> import Control.Lens
namely, the light-weight and elegant:
> import Lens.Simple
Check it out, it's even one character shorter!
The material in <http://hackage.haskell.org/package/lens-tutorial lens-tutorial>
will work fine if you make this substitution in the underlying
<http://hackage.haskell.org/package/lens-tutorial-1.0.0/docs/src/Control-Lens-Tutorial.html source>
and follow along as prompted.
As another illustration of the simplicity of the
fundamental van Laarhoven-O'Connor lens combinators - and their homogeneity with
@Control.Lens@ - note that the gloss
<https://github.com/michaelt/lens-family-simple/blob/master/examples/Pong.hs pong example>
from the @lens@ library examples directory - which continues to be
among the best introductory lens tutorials precisely by saying nothing -
requires only this abbreviating change of imports.
If you make that program more complicated,
you might of course end up needing
the more sophisticated material in @Control.Lens@ and
its immense mass of dependencies. On the other hand,
you might just need some of the additional material
present in the similarly demystifying
<http://hackage.haskell.org/package/microlens microlens>
or <http://hackage.haskell.org/package/microlens-th microlens-th> and
the associated modules.
This module was originally intended to simplify the use of packages that
follow the original promise of the van Laarhoven-O'Connor lenses.
/Correct practice is to export lenses without depending on a lens-library, where possible./
In basic cases these just use familiar @Prelude@ types, after all.
Examples of best practices in this respect are e.g. <http://hackage.haskell.org/package/lens-family-th lens-family-th> which
doesn't depend on @lens-family@ despite its name and pipes-related packages like
<http://hackage.haskell.org/package/pipes-bytestring pipes-bytestring>
and <http://hackage.haskell.org/package/pipes-group pipes-group>.
@Lens.Simple@ also re-exports @makeLenses@ and
other convenient TH incantations from Dan Burton's associated
<http://hackage.haskell.org/package/lens-family-th lens-family-th>.
michaelt/lens-simple