tagged-0.2: Provides newtype wrappers for phantom types to avoid unsafely passing dummy arguments

Portabilitygeneralized newtype deriving
MaintainerEdward Kmett <ekmett@gmail.com>






Tagged values

reproxy :: Proxy s -> Proxy tSource

Some times you need to change the tag you have lying around. Idiomatic usage is to make a new combinator for the relationship between the tags that you want to enforce, and define that combinator using retag.

 data Succ n
 reproxySucc :: Proxy n -> Proxy (Succ n)
 reproxySucc = reproxy

asProxyTypeOf :: a -> Proxy a -> aSource

asProxyTypeOf is a type-restricted version of const. It is usually used as an infix operator, and its typing forces its first argument (which is usually overloaded) to have the same type as the tag of the second.


proxy :: Tagged s a -> Proxy s -> aSource

Convert from a Tagged representation to a representation based on a Proxy.

unproxy :: (Proxy s -> a) -> Tagged s aSource

Convert from a representation based on a Proxy to a Tagged representation.