[Haskell-cafe] I miss OO

Derek Elkins derek.a.elkins at gmail.com
Wed Nov 25 16:06:09 EST 2009

On Wed, Nov 25, 2009 at 2:51 PM, Michael Mossey <mpm at alumni.caltech.edu> wrote:
> I'm fairly new to Haskell, and starting to write some big projects.
> Previously I used OO exclusively, mostly Python. I really miss the
> "namespace" capabilities... a class can have a lot of generic method names
> which may be identical for several different classes because there is no
> ambiguity.
> In my musical application, many "objects" (or in Haskell, data) have a time
> associated with them. In Python I would have an accessor function called
> "time" in every class.
> So if I have objects/data note1, cursor1, and staff1,
> Python:
>  note1.time()
>  cursor1.time()
>  staff1.time()
> Haskell needs something like
>  note_time note1
>  cursor_time cursor1
>  staff_time staff1
> which is a lot more visually disorganized.
> What's worse, I have a moderate case of RSI (repetitive strain injury) so I
> type slowly and depend on abbreviations a lot. I use the souped-up
> abbreviation capabilities of Emacs. Let's say I have a field/member-variable
> called orientedPcSet that is used across many classes. In Python, I can
> create an abbreviation for that and it is useful many times. In Haskell, I
> might need
> someType_orientedPcSet
> someOtherType_orientedPcSet
> thirdType_orientedPcSet
> which prevents me from using abbreviations effectively (especially the
> dynamic-completion feature). (It would help to make the underscore not part
> of word syntax, but that's not ideal.)
> So I'm thinking of moving to a scheme in Haskell using modules, most types
> being defined in their own modules, and doing qualified imports. Generic
> names like 'time' can be defined in each module w/o clashing. Then I have
> Note.time note1
> Cursor.time cursor1
> Staff.time staff1
> This is very useful because I can define abbreviations for the type name and
> for oft-used accessor function names and these abbrevs are more organized,
> easier to remember, and easier to combine.
> I would be interested in comments... is this a good way to do things? Am I
> trying too hard to impose OO on Haskell and is there a better way?

That is the way to do what you want and not a bad practice in general.
 There's nothing particularly OO about namespacing, for example, ML's
modules and functors are quite a bit more flexible in this regard than
typical OO languages.

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