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Comment by PieSquared | Hacker News Reader

Beat this short Arc snippet using map with a list comprehension:

  (def vector-dot-product (vector-1 vector-2)
    (map [* _1 _2] vector-1 vector-2))

That's from Light Makes Right the raytracer, I think. Equivalent python:

  def vectorDotProduct(vector1, vector2):
    return [x * y for x, y in zip(vector1, vector2)]

I'm pretty sure that the Lisp snippet above is neither harder to decipher nor longer. Though maybe that's just because Arc is nice.

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Agreed. This example highlights the great savings of the [... _ ...] syntax in Arc (which I'd imagine is a fairly common use-case, especially for map, filter, etc.).

Although ironically in this case, I'd probably use the following:

    def vectorDotProduct(vector1, vector2):
        return map(op.mul, vector1, vector2)

(where op has been imported previously using:

    import operator as op

)

I'm not really sure how idiomatic this is, but I find that 90% of the time when I use map in python, it's with the operator module.

in Haskell (and maybe ML), you might have

vectorDotProduct = map (*)

You probably meant:

vectorDotProduct = zipWith ( * )

(and this doesn't even include the sum)

map ( * ) has type Num a => [a] -> [a -> a] which is not really what the dot product should be.

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