Sorry, this was originally only sent to Atila, due to me pressing the
wrong button.
On 21/06/06, Atila Romero
instance Num a => Num [[a]] where fromInteger x = [[fromInteger x]] abs x = map (map abs) x (+) [ ] y = y (+) x [ ] = x (+) x y = zipWith (zipWith (+)) x y (*) x y = map (matrixXvector x) y where -- matrixXvector :: Num a => [[a]] -> [a] -> [[a]] matrixXvector m v = foldl vectorsum [] $ zipWith vectorXnumber m v -- vectorXnumber :: Num a => [a] -> a -> [a] vectorXnumber v n = map (n*) v -- vectorsum :: [a] -> [a] -> [a] vectorsum [] y = y vectorsum x [] = x vectorsum x y = zipWith (+) x y
Just a couple of comments: * You don't have to comment out the type signitures, they're perfectly valid in let and where clauses. * Infix functions, as well as being used infix, can be defined infix too. I.e., you could have written x * y = map (matrixXvector x) y. * Zipping the empty list with anything produces the empty list, so your two equations for (*) involving the empty list are redundant. * You define vectorsum, but don't seem to use it anywhere. -- -David House, dmhouse@gmail.com