[Haskell-beginners] type of zipWithPlus

[Russ Abbott]

When I define zipWithPlus at the top level of GHCi, the type is as shown.

> let zipWithPlus = zipWith (+)
zipWithPlus :: [Integer] -> [Integer] -> [Integer]

Why isn't it:  (Num a)  => a -> a-> a

  I was unable to find a way to get the type to be more general.  I tried
various declarations within the let using (Num a)  => a -> a-> a but none of
them were accepted.

Thanks.
-- Russ Abbott
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  Professor, Computer Science
  California State University, Los Angeles

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