Copyright | 2009-2015 Edward Kmett, 2012 Elliott Hird, 2004 Oleg Kiselyov and Chung-chieh Shan |
---|---|
License | BSD3 |
Maintainer | Edward Kmett <ekmett@gmail.com> |
Stability | experimental |
Portability | non-portable |
Safe Haskell | Trustworthy |
Language | Haskell98 |
Reifies arbitrary terms at the type level. Based on the Functional Pearl: Implicit Configurations paper by Oleg Kiselyov and Chung-chieh Shan.
http://www.cs.rutgers.edu/~ccshan/prepose/prepose.pdf
The approach from the paper was modified to work with Data.Proxy and streamline the API by Edward Kmett and Elliott Hird.
Usage comes down to two combinators, reify
and reflect
.
>>>
reify 6 (\p -> reflect p + reflect p)
12
The argument passed along by reify is just a data
, so all of the information needed to reconstruct your value
has been moved to the type level. This enables it to be used when
constructing instances (see Proxy
t =
Proxyexamples/Monoid.hs
).
This version is based on the "slow" path from the reflection
package,
but modified to work with the same Reifies
class as is provided by the "fast"
path, and to make sure the parameter is Typeable
.
This is necessary to work around the changes to Data.Typeable
in GHC HEAD.