From labra@lsi.uniovi.es  Thu Feb 18 07:17:58 1988
Date: Thu, 18 Feb 1988 08:17:58 +0100
From: Jose Emilio Labra Gayo labra@lsi.uniovi.es
Subject: Disjoint type classes

<PRE>I have a large program where I would like to include disjoint type classes
into a new type class.

My problem can be reduced to the following example (taken from [1]):

&gt;<i> class Num a =&gt; Dividable a
</I>&gt;<i>   where dividedBy :: a -&gt; a -&gt; a
</I>
&gt;<i> instance Fractional a =&gt; Dividable a where
</I>&gt;<i> dividedBy = (/)
</I>
&gt;<i> instance Integral a =&gt; Dividable a where
</I>&gt;<i>   dividedBy = div
</I>
Which doesn't work because Haskell doesn't detect that
&quot;Integral&quot; and &quot;Fractional&quot; are disjoint.

Is there a way to implement these type classes with current Haskell
implementations?

[1] K. Glynn, M. Sulzmann,  P.J. Stuckey
    Type Classes and Constraint Handling Rules
    <A HREF="http://www.cs.mu.oz.au/tr_submit/test/cover_db/mu_TR_2000_7.html">http://www.cs.mu.oz.au/tr_submit/test/cover_db/mu_TR_2000_7.html</A>

Best regards, Jose Labra





</PRE>

From labra@lsi.uniovi.es  Thu Feb 18 07:17:58 1988
From: labra@lsi.uniovi.es (Jose Emilio Labra Gayo)
Date: Thu, 18 Feb 1988 08:17:58 +0100
Subject: Disjoint type classes
Message-ID: <001601b205b3$20bd81c0$5d1f239c@ccu.uniovi.es>

I have a large program where I would like to include disjoint type classes
into a new type class.

My problem can be reduced to the following example (taken from [1]):

> class Num a => Dividable a
>   where dividedBy :: a -> a -> a

> instance Fractional a => Dividable a where
> dividedBy = (/)

> instance Integral a => Dividable a where
>   dividedBy = div

Which doesn't work because Haskell doesn't detect that
"Integral" and "Fractional" are disjoint.

Is there a way to implement these type classes with current Haskell
implementations?

[1] K. Glynn, M. Sulzmann,  P.J. Stuckey
    Type Classes and Constraint Handling Rules
    http://www.cs.mu.oz.au/tr_submit/test/cover_db/mu_TR_2000_7.html

Best regards, Jose Labra





From labra@lsi.uniovi.es  Thu Feb 18 07:17:58 1988
From: labra@lsi.uniovi.es (Jose Emilio Labra Gayo)
Date: Thu, 18 Feb 1988 08:17:58 +0100
Subject: Disjoint type classes
Message-ID: <001601b205b3$20bd81c0$5d1f239c@ccu.uniovi.es>

I have a large program where I would like to include disjoint type classes
into a new type class.

My problem can be reduced to the following example (taken from [1]):

> class Num a => Dividable a
>   where dividedBy :: a -> a -> a

> instance Fractional a => Dividable a where
> dividedBy = (/)

> instance Integral a => Dividable a where
>   dividedBy = div

Which doesn't work because Haskell doesn't detect that
"Integral" and "Fractional" are disjoint.

Is there a way to implement these type classes with current Haskell
implementations?

[1] K. Glynn, M. Sulzmann,  P.J. Stuckey
    Type Classes and Constraint Handling Rules
    http://www.cs.mu.oz.au/tr_submit/test/cover_db/mu_TR_2000_7.html

Best regards, Jose Labra





From labra@lsi.uniovi.es  Thu Feb 18 07:17:58 1988
From: labra@lsi.uniovi.es (Jose Emilio Labra Gayo)
Date: Thu, 18 Feb 1988 08:17:58 +0100
Subject: Disjoint type classes
Message-ID: <001601b205b3$20bd81c0$5d1f239c@ccu.uniovi.es>

I have a large program where I would like to include disjoint type classes
into a new type class.

My problem can be reduced to the following example (taken from [1]):

> class Num a => Dividable a
>   where dividedBy :: a -> a -> a

> instance Fractional a => Dividable a where
> dividedBy = (/)

> instance Integral a => Dividable a where
>   dividedBy = div

Which doesn't work because Haskell doesn't detect that
"Integral" and "Fractional" are disjoint.

Is there a way to implement these type classes with current Haskell
implementations?

[1] K. Glynn, M. Sulzmann,  P.J. Stuckey
    Type Classes and Constraint Handling Rules
    http://www.cs.mu.oz.au/tr_submit/test/cover_db/mu_TR_2000_7.html

Best regards, Jose Labra