[Haskell-cafe] Embedded Functions in Algebraic Data Types?

[Henning Thielemann]

On Sun, 10 Feb 2008, Luke Palmer wrote:

> Quite frequently.
>
> Here are a few examples from my own code:
>
> For "functional references" (representing a bidirectional function
> from a data type to a part of itself (for example the first element of
> a pair)).
>
> > data Accessor s a
> >     = Accessor { get :: s -> a
> >                , set :: a -> s -> s
> >                }
>
> My quantum computation arrow (really in the realm of "concrete, useful
> things", huh? :-)

The pattern seems to be common enough to be turned into a package.

http://www.haskell.org/haskellwiki/?title=Record_access&action=history