[Haskell-beginners] Equivalence of Inheritance

[Russ Abbott]

Ozgur pointed out this notition p at Man{}.  What I would like is something
like this.

type Man = Person at Man{}

type MensGroup = [Man]
*
-- Russ *



On Tue, Dec 14, 2010 at 1:45 PM, Michael Katelman <katelman at uiuc.edu> wrote:

> Without going too exotic, I see two choices. Keeping the single type
> Person makes what you are asking for, as far as I know, impossible
> (dependent types). For human readability you could consider
>
> type MensGroup = [Person]
> type WomensGroup = [Person]
>
> If you split Person into two types, Man and Woman, there are
> repercussions for the aggregate group type
>
> type Group = [Either Man Woman]
>
> -Mike
>
>
> On Tue, Dec 14, 2010 at 3:30 PM, Russ Abbott <russ.abbott at gmail.com>
> wrote:
> > Now that this is straightened out, I went back to what I was doing in the
> > first place and realized that I haven't solved my problem.
> > Given
> >
> > data Person =
> >       Man {name :: String, age :: Int, prostateCondition :: Condition}
> >   | Woman {name :: String, age :: Int, ovaryCondition    :: Condition}
> >
> > I'd like to define something like this.
> >
> > type MensGroup = [Man]
> >
> > Is there a way to do something like that?
> > -- Russ
> >
> >
> > On Tue, Dec 14, 2010 at 1:06 PM, Russ Abbott <russ.abbott at gmail.com>
> wrote:
> >>
> >> That's good. (It's more or less the way I was doing it.)  What I wanted
> to
> >> avoid was this.
> >>
> >> getGenderSpecificCondition (  Man _ _ cond) = cond
> >> getGenderSpecificCondition (Woman _ _ cond) = cond
> >>
> >> I know it seems like a small thing, but I would like to be able to write
> >> it like this.
> >>
> >> getGenderSpecificCondition p
> >>    | p == (Man _ _ cond) = cond
> >>    | p == (Woman _ _ cond) = cond
> >>
> >> But that's not legal syntax.  A pattern can't appear in that context.
> But
> >> this does the job.
> >>
> >> getGenderSpecificCondition :: Person -> Condition
> >> getGenderSpecificCondition p
> >>    | isMan p = prostateCondition p
> >>    | isWoman p = ovaryCondition p
> >>
> >> isMan (     Man _ _ cond) = True
> >> isMan _ = False
> >> isWoman (Woman _ _ cond) = True
> >> isWoman _ = False
> >>
> >> That works! prostateCondition and ovaryCondition are both defined on
> >> Person. (I'm surprised to see that.)
> >>
> >> *Person> Group [Man "Harry" 32 OK, Woman "Sally" 29 Good]
> >> Harry(32, OK)
> >> Sally(29, Good)
> >>
> >> Also
> >>
> >> *Person> prostateCondition (Woman "Sally" 29 Good)
> >> *** Exception: No match in record selector prostateCondition
> >> *Person> prostateCondition (Man "Harry" 29 Good)
> >> Good
> >>
> >> -- Russ
> >>
> >>
> >> On Tue, Dec 14, 2010 at 12:31 PM, Michael Katelman <katelman at uiuc.edu>
> >> wrote:
> >>>
> >>> Perhaps this?
> >>>
> >>> https://gist.github.com/741048
> >>>
> >>> -Mike
> >>>
> >>> On Tue, Dec 14, 2010 at 2:27 PM, Russ Abbott <russ.abbott at gmail.com>
> >>> wrote:
> >>> > What I'm after is a version of my example that compiles.  Can you
> make
> >>> > one?
> >>> >
> >>> > -- Russ
> >>> >
> >>> >
> >>> > On Tue, Dec 14, 2010 at 12:18 PM, Antoine Latter <aslatter at gmail.com
> >
> >>> > wrote:
> >>> >>
> >>> >> Sorry, I really don't know enough about what you're after to attempt
> >>> >> that.
> >>> >>
> >>> >> But you'll need to change you're signatures of the form:
> >>> >>
> >>> >> > function :: Person -> Foo
> >>> >>
> >>> >> to something of the form:
> >>> >>
> >>> >> > function :: Person p => p -> Foo
> >>> >>
> >>> >> Because again, a type class can not be used as a type.
> >>> >>
> >>> >> Antoine
> >>> >>
> >>> >> On Tue, Dec 14, 2010 at 2:12 PM, Russ Abbott <russ.abbott at gmail.com
> >
> >>> >> wrote:
> >>> >> > What got fouled up is all the adjustments I had to make to the
> other
> >>> >> > declarations.
> >>> >> > Can you complete the example so that it compiles using
> >>> >> >
> >>> >> > class Person p where ...
> >>> >> >
> >>> >> > I'd very much like to see an example that actually compiles.
> >>> >> >
> >>> >> > Thanks.
> >>> >> > -- Russ
> >>> >> >
> >>> >> > On Tue, Dec 14, 2010 at 11:58 AM, Antoine Latter
> >>> >> > <aslatter at gmail.com>
> >>> >> > wrote:
> >>> >> >>
> >>> >> >> On Tue, Dec 14, 2010 at 1:52 PM, Russ Abbott
> >>> >> >> <russ.abbott at gmail.com>
> >>> >> >> wrote:
> >>> >> >> > If gender is a field in a Person type, then a Person must have
> >>> >> >> > both
> >>> >> >> > an
> >>> >> >> > ovaryCondition and a prostateCondition.  That seems awkward.
> >>> >> >> > Regarding
> >>> >> >> >      class Person p where
> >>> >> >> > I started down that path but got completely fouled up.
> >>> >> >>
> >>> >> >> How did this get fouled up? Every class declaration must take
> >>> >> >> arguments - here, 'p' is the argument for the class.
> >>> >> >>
> >>> >> >> Thanks,
> >>> >> >> Antoine
> >>> >> >
> >>> >> >
> >>> >
> >>> >
> >>> > _______________________________________________
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> >>> > Beginners at haskell.org
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> >>> >
> >>> >
> >>
> >
> >
>
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