Package Info


Simplified import of elementary lens-family combinators


This module, < Lens.Simple>, just re-exports the main modules from Russell O'Connor's < lens-family> package, the original van Laarhoven-O'Connor lens library. 'lens-family' is particularly remarkable for its minute number of dependencies: (apart from < 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 < 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 < lens-tutorial> will work fine if you make this substitution in the underlying < 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

< 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 < microlens> or < 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. < lens-family-th> which doesn't depend on 'lens-family' despite its name and pipes-related packages like < pipes-bytestring> and < pipes-group>.

'Lens.Simple' also re-exports convenient TH incantations like 'makeLenses' from Dan Burton's associated < lens-family-th>. .

License: BSD-3-Clause



Package Version Update ID Released Package Hub Version Platforms Subpackages info GA Release 2018-07-30 15
  • AArch64
  • ppc64le
  • x86-64
  • ghc-lens-simple
  • ghc-lens-simple-devel