proxied-0.3.1: README.md

# `proxied`
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[Hackage: proxied]:
  http://hackage.haskell.org/package/proxied
  "proxied package on Hackage"
[Haskell.org]:
  http://www.haskell.org
  "The Haskell Programming Language"
[tl;dr Legal: BSD3]:
  https://tldrlegal.com/license/bsd-3-clause-license-%28revised%29
  "BSD 3-Clause License (Revised)"

`proxied` is a simple library that exports a function to convert constant functions to ones that take a `proxy` value in the `Data.Proxied`. This is useful for retrofiting typeclasses that have functions that return a constant value for any value of a particular type (but still need to consume some value, since one of the parameterized types must appear in a typeclass function). Often, these functions are given `undefined` as an argument, which might be considered poor design.

 `Proxy`, however, does not carry any of the error-throwing risks of `undefined`, so it is much more preferable to take `Proxy` as an argument to a constant function instead of `undefined`. Unfortunately, `Proxy` wasn't included in `base` until GHC 7.8, so many of `base`'s typeclasses still contain constant functions that aren't amenable to passing `Proxy`. `proxied` addresses this issue by providing variants of those typeclass functions that take an explicit `proxy` value.

This library also contains the `Data.Proxyless` module, which works in the opposite direction. That is, one can take functions which take `Proxy` (or `undefined`) as an argument and convert them to functions which take no arguments. This trick relies on the `-XTypeApplications` extension, so it is only available with GHC 8.0 or later.