[Haskell-beginners] Re: Integer factorization
Heinrich Apfelmus
apfelmus at quantentunnel.de
Sat Mar 14 04:39:18 EDT 2009
Colin Paul Adams wrote:
>>>>>> "Heinrich" == Heinrich Apfelmus <apfelmus at quantentunnel.de> writes:
>
> Heinrich> Abstraction is the one driving force for very short
> Heinrich> names. For example, take the definition of foldr
>
> Heinrich> foldr f z [] = z foldr f z (x:xs) = f x (foldr f z
> Heinrich> xs)
>
> Heinrich> Since this function is polymorphic, so f , z and the xs
> Heinrich> can be anything, using more "descriptive" variable names
> Heinrich> is simply not possible; the key point of fold is its
> Heinrich> generality.
>
> Wouldn't unit be a better descriptive name than z?
I have never heard of a unit in relation to fold , I'm afraid. Monoids
and groups have units, as do physicists and a few other mathematical
structures.
While z is indeed quite often the unit of a monoid, for instance in
sum = foldr (+) 0
product = foldr (*) 1
concat = foldr (++) []
it doesn't have to be the unit of a monoid.
Regards,
apfelmus
--
http://apfelmus.nfshost.com
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