[Haskell-cafe] Mapping over multiple values of a list at once?

[haskell at kudling.de]

Hi,

Imagine you have a list with n-values. You are asked to iterate over the list and calculate the average value of each 3 neighbouring values.

For example, starting from

[4,3,2,6,7]

you need to find the averages of

4,3,2 and 3,2,6 and 2,6,7

resulting in 

[3,4,5]

What is the most elegant way to do that?
The naive ansatz to use "(!!") excessively sounds pretty inefficient.

Bye,
Lenny