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Today's Topics:
1. Re: Type unions (Russ Abbott)
2. Re: Type unions (Hector Guilarte)
3. Re: Equivalence of Inheritance (Russ Abbott)
----------------------------------------------------------------------
Message: 1
Date: Tue, 14 Dec 2010 13:10:35 -0800
From: Russ Abbott <russ.abb...@gmail.com>
Subject: Re: [Haskell-beginners] Type unions
To: Tobias Brandt <tob.bra...@googlemail.com>
Cc: beginners <beginners@haskell.org>
Message-ID:
<aanlktimyeea9-rxrvf_tkrg2loyhnjkm+app6n0oo...@mail.gmail.com>
Content-Type: text/plain; charset="iso-8859-1"
My typo started this most recent confusion. When I wrote
data AorB = A | B
compiles with error.
That raises the question of what it really means!
I meant to say
data AorB = A | B
compiles *without *error.
That raises the question of what it really means!
*
-- Russ *
On Tue, Dec 14, 2010 at 1:04 PM, Tobias Brandt <tob.bra...@googlemail.com>wrote:
> On 14 December 2010 22:02, Hector Guilarte <hector...@gmail.com> wrote:
> > Tobias you replied at the same time I was answering, you did explained
> what
> > is happening,
> > however, you said something which isn't right. As I mentioned before,
> "Type
> > Constructors" and
> > "Value Constructors" are in different scopes, and so, their names can be
> > used again...
> > if you don't believe me, give it a try with this example.
>
> I believe you. As I said, I was talking crap :-)
>
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Message: 2
Date: Tue, 14 Dec 2010 16:59:43 -0430
From: Hector Guilarte <hector...@gmail.com>
Subject: Re: [Haskell-beginners] Type unions
To: russ.abb...@gmail.com
Cc: beginners <beginners@haskell.org>
Message-ID:
<aanlktim8lp6_4qgvojehxzlj0vsjsy5z5eyvdzab3...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
But did you already understand what's happening?
> data AorB = A | B
is pretty much like an enumeration the same as
> data DayOfTheWeek = Monday | Tuesday | Wednesday | ... | Sunday
it stores no values of any type, you could even have DayOfTheWeek as
a constructor in the same declaration of the data DayOfTheWeek, because they
are
in different scopes:
> data DayOfTheWeek = Monday | Tuesday | Wednesday | ... | Sunday
| DayOfTheWeek
and by no means, that A or B on the right hand side of your data AorB are
referencing the
data A nor the data B...
In the end, you could have:
data A = Aconstructor Int
data B = Bconstructor Int
data AorB = A A | B B
f :: Int -> AorB
f x
| even x = A (Aconstructor x)
| otherwise = B (Bconstructor x)
I just added a Value to each constructor of the data AorB, which happens to
be
named the same as the value they store...
What I'm about to do is something I haven't tried, but I don't see why it
shouldn't
compile:
> data Try = Int Int
in data Try you have a constructor named Int, and it has a value of type
Int,
I'm trying to explain it the best I can, but I don't know if I managed to do
it
clearly, please let me know if there's something where I wasn't clear
enough.
Hector
On Tue, Dec 14, 2010 at 4:40 PM, Russ Abbott <russ.abb...@gmail.com> wrote:
> My typo started this most recent confusion. When I wrote
>
> data AorB = A | B
>
> compiles with error.
> That raises the question of what it really means!
>
>
> I meant to say
>
> data AorB = A | B
>
> compiles *without *error.
> That raises the question of what it really means!
>
> *
> -- Russ *
>
>
> On Tue, Dec 14, 2010 at 1:04 PM, Tobias Brandt
> <tob.bra...@googlemail.com>wrote:
>
>> On 14 December 2010 22:02, Hector Guilarte <hector...@gmail.com> wrote:
>> > Tobias you replied at the same time I was answering, you did explained
>> what
>> > is happening,
>> > however, you said something which isn't right. As I mentioned before,
>> "Type
>> > Constructors" and
>> > "Value Constructors" are in different scopes, and so, their names can be
>> > used again...
>> > if you don't believe me, give it a try with this example.
>>
>> I believe you. As I said, I was talking crap :-)
>>
>
>
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Message: 3
Date: Tue, 14 Dec 2010 13:30:32 -0800
From: Russ Abbott <russ.abb...@gmail.com>
Subject: Re: [Haskell-beginners] Equivalence of Inheritance
To: Michael Katelman <katel...@uiuc.edu>
Cc: beginners <beginners@haskell.org>
Message-ID:
<aanlktinzhz5h1w3ukh=0ssheo74qadojwfuzsn0fh...@mail.gmail.com>
Content-Type: text/plain; charset="iso-8859-1"
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.abb...@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 <katel...@uiuc.edu>wrote:
>
>> Perhaps this?
>>
>> https://gist.github.com/741048
>>
>> -Mike
>>
>> On Tue, Dec 14, 2010 at 2:27 PM, Russ Abbott <russ.abb...@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 <aslat...@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.abb...@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 <aslat...@gmail.com
>> >
>> >> > wrote:
>> >> >>
>> >> >> On Tue, Dec 14, 2010 at 1:52 PM, Russ Abbott <russ.abb...@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
>> >> >
>> >> >
>> >
>> >
>> > _______________________________________________
>> > Beginners mailing list
>> > Beginners@haskell.org
>> > http://www.haskell.org/mailman/listinfo/beginners
>> >
>> >
>>
>
>
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