Re: darcs patch: Added list operations for arrows

Am Freitag, 31. Oktober 2008 14:21 schrieben Sie:

On Fri, 2008-10-31 at 13:26 +0100, Wolfgang Jeltsch wrote:

...

Am Donnerstag, 30. Oktober 2008 18:17 schrieb Peter Collingbourne:

...

Hello,

This patch adds two arrow combinators which I have found useful: mapA (equivalent of map) and filterA (equivalent of filter).

Thu Oct 30 16:50:02 GMT 2008 Peter Collingbourne * Added list operations for arrows

Thanks,

Hello,

wouldn’t it be better to stop using identifiers containing categorization in form of single letters like filterA, mappend, etc.? I’d say, we have the module system for this: Monoid.append, Arrow.filter, etc. Is someone interested in cleaning up the library interfaces in this regard while maintaining compatibility?

Here here!

'A.filter' rather than 'filterA' (with a suitable qualified import).

Duncan

Hmm, is this meant ironically or seriously? Sorry, I just don’t know. A.filter has the advantage over filterA that it has more structure: the module name expresses the general topic and the actual name denotes the concrete function. In addition, you can drop the qualification if there is no ambiguity. Another point is that filterA uses just a single letter for “arrow”. This concept quickly leads to ambiguities. For example, in mappend, the “m” stands for “monoid” while in msum, it stands for “monad”. Something like filterArrow would have the disadvantage that it is longer. With qualified imports, the user of the library can decide whether to use a single letter (A.filter) or something more descriptive (Arrow.filter). I think, this topic came up a while ago on some Haskell list already and there were several people arguing that employing the module system as I suggest was the better way. Best wishes, Wolfgang