Re: [Haskell-cafe] Re: is there a more concise way to generate helper functions for a datatype built on records?

On Mon, 26 Nov 2007, apfelmus wrote:

Benedikt Huber wrote:

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type Upd a = a -> a data Ref cx t = Ref { select :: cx -> t , update :: Upd t -> Upd cx }

Functional references are also called "lens", I'm going to use that term from now on.

As a minor note, I somehow prefer a single primitive

data Lens s a = Lens { focus :: s -> (a, a -> s) }

put :: Lens s a -> a -> s -> s put x = flip $ snd . focus x

get :: Lens s a -> s -> a get x = fst . focus x

update :: Lens s a -> (a -> a) -> (s -> s) update x f s = let (a,g) = focus x s in g (f a)

I proposed something similar on http://www.haskell.org/haskellwiki/Record_access