hello -- this is mostly a question for roman, or don, i guess. suppose i have a list of similarly-sized vectors, and i want to add them up (possibly with coefficients), to yield a result vector. something like module Main where import qualified Data.Vector.Generic as V import qualified Data.Vector.Unboxed as UV type Vec = UV.Vector Double axpy :: Double -> Vec -> Vec -> Vec axpy a x y = V.zipWith (+) (V.map (* a) x) y sumVecs :: [(Double, Vec)] -> Vec sumVecs axs = let (a, x) = head axs in foldl adder (V.map (* a) x) (tail axs) where adder :: Vec -> (Double, Vec) -> Vec adder v1 (a, x) = axpy a x v1 how to i write this in a way which ensures recycling / fusion, e.g. in-place updates? best regards, ben