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module Data.Accessor.Private where
{- |
The accessor function we use,
has a record value as first argument
and returns the content of a specific record field
and a function that allows to overwrite that field with a new value.
In former version of a package
we used a function that resembled the state monad.
However this required to use an 'undefined'
in the implementation of the @get@ function.
-}
newtype T r a = Cons {decons :: r -> (a, a -> r)}
compose :: T a b -> T b c -> T a c
compose f g = Cons $ \ aOld ->
let (bOld, aSetB) = decons f aOld
(cOld, bSetC) = decons g bOld
in (cOld, aSetB . bSetC)
self :: T r r
self = Cons $ \r -> (r, id)
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