# proxied

Make functions consume Proxy instead of undefined https://github.com/RyanGlScott/proxied

Version on this page: | 0.2 |

LTS Haskell 8.15: | 0.2 |

Stackage Nightly 2017-05-26: | 0.3 |

Latest on Hackage: | 0.3 |

**Ryan Scott**

**Ryan Scott**

#### Module documentation for 0.2

`proxied`

[][Haskell.org] [][tl;dr Legal: BSD3]

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`

was 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.

## Changes

## 0.3

- Update for GHC 8.2
*Since*Happily, the new type signature for`typeRep#`

,`typeNatTypeRep`

, and`typeSymbolTypeRep`

are no longer exported from`base`

,`theTypeRep#`

,`theTypeNatTypeRep`

, and`theTypeSymbolTypeRep`

are now synonyms for`theTypeRep`

`GHC.OverloadedLabels.fromLabel`

is now exactly the same as`theFromLabel`

, so the latter is now a synonym for the former - Use explicit kind variable binders in
`Data.Proxyless`

- Use explicit
`forall`

s in`Data.Proxied`

for consistency

## 0.2

- Added the
`Data.Proxyless`

module - Added
`proxyHashed`

to`Data.Proxied`

### 0.1.1

Enabled

`Safe`

## 0.1

- Initial commit