[Haskell-cafe] Basic question concerning the category Hask (was: concerning data constructors)

Jonathan Cast jonathanccast at fastmail.fm
Sun Jan 6 12:54:15 EST 2008

On 6 Jan 2008, at 3:55 AM, Yitzchak Gale wrote:

> I wrote:
>>> What goes wrong with finite coproducts? The obvious thing to
>>> do would be to take the disjoint union of the sets representing the
>>> types, identifying the copies of _|_.
> Jonathan Cast wrote:
>> This isn't a coproduct.  If we have f x = 1 and g y = 2, then there
>> should exist a function h such that h . Left = f and h . Right = g...
>> But by your rule, Left undefined = Right undefined...
>> Which is a contradiction...
> OK, thanks.
>> Unless, of course,
>> your require your functions to be strict --- then both f and g above
>> become illegal, and repairing them removes the problem.
> You don't have to make them illegal - just not part
> of your notion of "coproduct".

We're talking past each other --- what is the distinction you are  


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