Thanks. I tried the first two, which worked.

Previously I had tried:

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

<interactive>:1:5:
Illegal signature in pattern: (Num a) => [a] -> [a] -> [a]
Use -XScopedTypeVariables to permit it

I tried setting -XScopedTypeVariables. When I ran it again I got a different error message:

Prelude> let (zipWithPlus :: Num a => [a] -> [a] -> [a]) = zipWith (+)

<interactive>:1:5:
    Illegal polymorphic or qualified type:
      forall a. (Num a) => [a] -> [a] -> [a]
    Perhaps you intended to use -XRankNTypes or -XRank2Types
    In a pattern type signature: (Num a) => [a] -> [a] -> [a]
    In the pattern: zipWithPlus :: (Num a) => [a] -> [a] -> [a]
    In a pattern binding:
        (zipWithPlus :: (Num a) => [a] -> [a] -> [a]) = zipWith (+)

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

Google voice: 424-242-USA0 (last character is zero)
blog: http://russabbott.blogspot.com/
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______________________________________

On Thu, Sep 30, 2010 at 12:48 PM, Daniel Fischer <daniel.is.fischer@web.de> wrote:

let zipWithPlus xs ys = zipWith (+) xs ys