help need

Benny [email protected]
Sun, 14 Apr 2002 16:20:35 +1200


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type Poly =3D [Float]

addPoly::Poly->Poly->Poly
addPoly x y =3D zipWith (+) x y

instance (Float a) =3D> Num (Poly a) where
                   x + y =3D addPoly x y


I got the "Cannot use type synonym in instance head" error message when =
I was trying to compile the above code. Can you tell me why and how to =
solve it?

Cheers

Benny

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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML><HEAD>
<META http-equiv=3DContent-Type content=3D"text/html; charset=3Dbig5">
<META content=3D"MSHTML 5.50.4134.100" name=3DGENERATOR>
<STYLE></STYLE>
</HEAD>
<BODY bgColor=3D#ffffff>
<DIV>type Poly =3D [Float]</DIV>
<DIV>&nbsp;</DIV>
<DIV>addPoly::Poly-&gt;Poly-&gt;Poly<BR>addPoly x y =3D zipWith (+) x =
y</DIV>
<DIV>&nbsp;</DIV>
<DIV>instance (Float a) =3D&gt; Num (Poly a)=20
where<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbs=
p;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;=20
x + y&nbsp;=3D addPoly x y</DIV>
<DIV>&nbsp;</DIV>
<DIV>&nbsp;</DIV>
<DIV>I got the "Cannot use type synonym in instance head" error message =
when I=20
was trying to compile the above code. Can you tell me why and how to =
solve=20
it?</DIV>
<DIV>&nbsp;</DIV>
<DIV>Cheers</DIV>
<DIV>&nbsp;</DIV>
<DIV>Benny</DIV></BODY></HTML>

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