classes
Cagdas Ozgenc
co19@cornell.edu
Fri, 31 Aug 2001 12:56:32 +0300
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Hi,
I am a newbie, so I might be making nonsense.
In the following definiton:
class Eq a where
(=3D=3D) :: a -> a -> Bool
Why do we conlude that both of the "a" refer to the same type? =
Apparently using different types that both belonging to class Eq results =
in an error. For example
65 =3D=3D 'a'
It doesn't make much sense at first, however, how do you go by =
implementing multiple polymorphism?
Secondly, why does Haskell distinguish between a Type and a Class? There =
seems to be no benefit of such approach.
Thirdly, is it possible to define meta-classes in Haskell?
Thanks
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<HTML><HEAD>
<META content=3D"text/html; charset=3Diso-8859-1" =
http-equiv=3DContent-Type>
<META content=3D"MSHTML 5.00.3103.1000" name=3DGENERATOR>
<STYLE></STYLE>
</HEAD>
<BODY bgColor=3D#ffffff>
<DIV><FONT face=3DArial size=3D2>Hi,</FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=3DArial size=3D2>I am a newbie, so I might be making=20
nonsense.</FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=3DArial size=3D2>In the following =
definiton:</FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=3DArial size=3D2>class Eq a where</FONT></DIV>
<DIV><FONT face=3DArial size=3D2> (=3D=3D) :: a -> =
a ->=20
Bool</FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=3DArial size=3D2>Why do we conlude that both of the "a" =
refer to the=20
same type? Apparently using different types that both belonging to class =
Eq=20
results in an error. For example</FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=3DArial size=3D2>65 =3D=3D 'a'</FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=3DArial size=3D2>It doesn't make much sense at first, =
however, how=20
do you go by implementing multiple polymorphism?</FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=3DArial size=3D2>Secondly, why does Haskell distinguish =
between a=20
Type and a Class? There seems to be no benefit of such =
approach.</FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=3DArial size=3D2>Thirdly, is it possible to define =
meta-classes in=20
Haskell?</FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=3DArial size=3D2>Thanks</FONT></DIV></BODY></HTML>
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