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List:       haskell-cafe
Subject:    Re: [Haskell-cafe] Re: Functional progr., infinity, and the Universe
From:       Nils Anders Danielsson <nad () cs ! chalmers ! se>
Date:       2006-06-26 12:32:33
Message-ID: x2t7fyhsumfy.fsf () matsu ! medic ! chalmers ! se
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On Sat, 24 Jun 2006, Paul Hudak <paul.hudak@yale.edu> wrote:

> Hmmm... never tried to write all this down in one place before, but I
> think this covers all cases:
>
> A partial list is one that ends in _|_.
> A total list is one that ends in [].
> A finite list is either partial or total.
> Any other list is infinite.

To confuse the picture more I'd like to point out that some use
different terminology:

* A strictly (spine-) partial list is one that ends in _|_.
* A (spine-) total list is one that ends in [] or doesn't end at all.
* A finite list is one that ends (with [] or _|_).
* An infinite list is one that doesn't end.

The two concepts (finite/infinite and total/strictly partial) are
orthogonal, and both partition the set of all lists.

And of course this generalises to other data types:

Finite: x is finite if it is contained in all ω-chains whose lubs are x.
Infinite: Not finite.
Total: No bottoms.
Strictly partial: Not total.
Partial: Total or strictly partial.

-- 
/NAD


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