|> > data Ref cx t
|> > = Ref
|> > {
|> > select :: cx -> t
|> > , update :: (t -> t) -> cx -> cx
|> > }
|>
|> A Ref is a bit like a typed and composable incarnation of apfelmus's
|> indices, or a wrapper around Tillmann's change* functions, containing
|> not only a setter but also the accompanying getter.
|
|That's a neat idiom. I wonder how far one could usefully generalize it.
you might find Koji Kagawa's papers interesting:
http://guppy.eng.kagawa-u.ac.jp/~kagawa/publication/index-e.html
in particular
Mutable Data Structures and Composable References
in a Pure Functional Language , Koji Kagawa, In SIPL '95:
State in Programming Languages, San Francisco, USA, January 1995.
Compositional References for Stateful Functional Programming,
Koji Kagawa, ICFP 1997, June 1997, Amsterdam, the Netherlands.
claus
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