filtroBooleano :: [Bool] -> [a] -> [Maybe a]

λ> filtroBooleano [True,False,True] "Sevilla"
[Just 'S',Nothing,Just 'v']
λ> filtroBooleano (repeat True) "abc"
[Just 'a',Just 'b',Just 'c']
λ> take 3 (filtroBooleano (repeat True) [1..])
[Just 1,Just 2,Just 3]
λ> take 3 (filtroBooleano (repeat False) [1..])
[Nothing,Nothing,Nothing]
λ> take 3 (filtroBooleano (cycle [True,False]) [1..])
[Just 1,Nothing,Just 3]

-- 1ª solución (por comprensión):
filtroBooleano1 :: [Bool] -> [a] -> [Maybe a]
filtroBooleano1 xs ys = [f (x,y) | (x,y) <- zip xs ys]
    where f (x,y) | x         = Just y
                  | otherwise = Nothing

-- 2ª solución (con zipWith):
filtroBooleano2 :: [Bool] -> [a] -> [Maybe a]
filtroBooleano2 = zipWith f
    where f x y  | x         = Just y
                 | otherwise = Nothing

-- 3ª solución (con zipWith y lambda):
filtroBooleano3 :: [Bool] -> [a] -> [Maybe a]
filtroBooleano3 = zipWith (\x y -> if x then Just y else Nothing)

-- 4ª solución (por recursión):
filtroBooleano4 :: [Bool] -> [a] -> [Maybe a]
filtroBooleano4 (x:xs) (y:ys) | x         = Just y : filtroBooleano4 xs ys
                              | otherwise = Nothing : filtroBooleano4 xs ys
filtroBooleano4 _ _                       = []