[Haskell-cafe] ANNOUNCE: partial-lens 0.0.1

[Erik Hesselink]

How does this relate to the Maybe lenses in fclabels [1]?

Erik

[1] http://hackage.haskell.org/packages/archive/fclabels/1.0.4/doc/html/Data-Label-Maybe.html

On Wed, Dec 21, 2011 at 04:54,  <roconnor at theorem.ca> wrote:
> Do you miss null references from your old imperative programming days? Wish
> that the worlds best imperative language had null references?  Now your
> wishes have come true with the new partial-lens package!
>
> partial-lens augment edwardk's data-lens package with partial lens. Partial
> lenses are like regular lenses but have the possibility of not referencing
> anything.  In other words, null references are possible.  One notable
> different with null references from this package is that you can set them
> without getting a run-time error.  Instead setting a null reference is a
> no-op; however it is possible to determine if setting failed from the return
> value of the assignment operation.
>
> Actually I don't have any applications for partial lenses myself, so if you
> find this library useful, please let me know.  I wrote this mostly because
> we know what partial lenses are in theory (they are the coalgebras of the
> (Identity :+: Store b) comonad) but I wanted to see what a real library
> would look like.
>
> --
> Russell O'Connor                                      <http://r6.ca/>
> ``All talk about `theft,''' the general counsel of the American Graphophone
> Company wrote, ``is the merest claptrap, for there exists no property in
> ideas musical, literary or artistic, except as defined by statute.''
>
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