[Haskell-cafe] Cost: (:) vs head

michael rice nowgate at yahoo.com
Sun Sep 12 09:10:27 EDT 2010

Hi Henning,

Thanks for the tip, I'll check it out.

A related but more general question: on average, what's more efficient, pattern matching or function calls?


--- On Sun, 9/12/10, Henning Thielemann <schlepptop at henning-thielemann.de> wrote:

From: Henning Thielemann <schlepptop at henning-thielemann.de>
Subject: Re: [Haskell-cafe] Cost: (:) vs head
To: "michael rice" <nowgate at yahoo.com>
Cc: haskell-cafe at haskell.org
Date: Sunday, September 12, 2010, 8:47 AM

michael rice schrieb:
> Which of these would be more costly for a long list?
> f :: [Int] -> [Int]
> f [x] = [x]
> f (x:xs) = x + (head xs) : f xs
> f :: [Int] -> [Int]
> f [x] = [x]
> f (x:y:xs) = x + y : f (y:xs)

What about empty lists? How about
  zipWith (+) xs (drop 1 xs ++ [0]) ?

Since I often need to combine adjacent list elements, I have defined
mapAdjacent in utility-ht.

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