[Haskell-cafe] Re: Comments from OCaml Hacker Brian Hurt

ChrisK haskell at list.mightyreason.com
Thu Jan 15 18:54:09 EST 2009

Thomas DuBuisson wrote:
>> How does forcing them to learn proposed terminology such as `Appendable'
>> help here?  Learners of Haskell do still need to learn what the new word
>> means.
> The contention is that 'Appendable' is an intuitive naming that people
> will already have a rudimentary grasp of.  This as opposed to Monoid,
> which absolutely requires looking up for the average coder.

Intuition tells me:

* 'Appendable' add an element to the back of a (finite) linear collection.
* There is a 'Prependable' somewhere that add the element to the front.
* There is an inverse 'pop' or 'deque' operation nearby.

Absolutely none of those things are true.  Let's try for 'Mergeable'

* mconcat joins two collections, not a collection and an element.
* Is should be a split operation.

The above is true for the list instance, but false in general.  Look at the 
instances already given that violate the "collection" idea:

> Monoid Any
> Monoid All
> Monoid (Last a)
> Monoid (First a)
> Num a => Monoid (Product a)
> Num a => Monoid (Sum a)

And I don't even see an (Ord a)=>(Max a) or a Min instance.

So the original article, which coined 'Appendable', did so without much thought 
in the middle of a long post.  But it does show the thinking was about 
collections and there is one ONE instance of Monoid at


that is about a collection (Monoid ([] a)) that has a split operation.


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