[Haskell-cafe] Clearly, Haskell is ill-founded

Andrew Coppin andrewcoppin at btinternet.com
Tue Jul 10 16:07:45 EDT 2007

Stefan O'Rear wrote:
> On Tue, Jul 10, 2007 at 08:08:52PM +0100, Andrew Coppin wrote:
>> Erm... Wait a sec... coroutines, comonads, coprograms, codata... what in 
>> the name of goodness does "co" actually *mean* anyway??
> Nothing.
> When mathematicians find a new thing completely unlike an OldThing, but
> related by some symmetry, they often call the new thing a CoOldThing.
> Data can only be constructed using constructors, but can be
> deconstructed using recursive folds;
> Codata can only be deconstructed using case analysis, but can be
> constructed using recursive unfolds.
> Monads keep things inside.
> Comonads keep things outside.
> Homology theory studies the boundaries of shapes.
> Cohomology theory studies the insides of curves.
> ...

...so it's similar to the term "normal"?

As in

Normal vector - a vector having unit length.
Normal distribution - a common monomodal distribution following a 
characterstic Gaussian bell curve.
Normal subgroup - a subset of a group such that all elements of it 
commute with the all elements of the whole group.

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