[Haskell-cafe] How to define an operation in terms of itself (but of different type)?

Brandon S. Allbery KF8NH allbery at ece.cmu.edu
Sat Jan 24 01:24:33 EST 2009

On 2009 Jan 23, at 17:58, Olex P wrote:
> class Vector v where
>     (^+^)       :: v -> v -> v
> class Matrix m where
>     (^+^)     :: m -> m -> m

You can't reuse the same operator in different classes.  Vector  
"owns" (^+^), so Matrix can't use it itself.  You could say

 > instance Matrix m => Vector m where
 >   (^+^) = ...

allowing Matrix to "inherit" Vector's operator (or turn it around the  
other way, make it Matrix then make Vector a Matrix), but that's only  
linguistically possible, not necessarily mathematically sane.

brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allbery at kf8nh.com
system administrator [openafs,heimdal,too many hats] allbery at ece.cmu.edu
electrical and computer engineering, carnegie mellon university    KF8NH

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