Proposal: Add Compositor class as superclass of Arrow

Ashley Yakeley ashley at
Mon Oct 22 22:23:29 EDT 2007

On Sun, 2007-10-21 at 22:04 +0200, apfelmus wrote:
> Twan van Laarhoven wrote:
> > My proposal would be the following. The important things are that:
> >  1. It incorporates Conal's deep arrow,
> >  2. as well as everything that is needed for functional 
> > references/lenses and bijective/invertible functions.
> I'd opt for more research for that proposal to answer the following 
> essential questions:
> - Do the classes correspond to already-known categories, i.e. are the 
> class names optimal?
> - What laws do we expect to hold?
> - Are the signatures minimal, i.e. does there exist a smaller set of 
> combinators that still achieves the intended effect? Are the signatures 
> complete, i.e. can the intended effect always expressed with the given 
> combinators?
> - Plenty and useful examples? At least enough examples that fit in the 
> fine grained hierarchy but cannot be fit into a coarser grained one so 
> as to demonstrate the necessity of a fine grained hierarchy.

I tend to agree. Rather than being part of this change, it might be
better for someone to work on this as a separate library, and then make
a proposal to redefine the Arrow classes once it's well-understood and

Ashley Yakeley

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