LP 2017-10-23

p1.hs

-- Diccionari de Strings a Ints amb funcions d'ordre superior
-- i valors per defecte. 


type Dict = (String -> Int)

-- Versió 1

create :: Int -> Dict
create def = \key -> def

search :: Dict -> String -> Int
search dic key = dic key

insert :: Dict -> String -> Int -> Dict 
insert dic key val = \x -> if key == x then val else search dic x


-- Versió 2

create :: Int -> Dict
create = const 

search :: Dict -> String -> Int
search = ($)

insert :: Dict -> String -> Int -> Dict 
insert dic key val x 
    | key == x      = val 
    | otherwise     = dic x


-- Exercici: Afegir el erase
erase :: Dict -> String -> Dict

p2.hs

-- Llistes per comprensió

doblats xs = [2*x | x <- xs] 

doblats xs = [d | x <- xs, let d = 2*x] 

doblatsIMultiplesDe3 xs = [2*x | x <- xs, x `mod` 3 == 0]

prodCart n = [(i, j) | i <- [1..n], j <- [1..n]]

tripletesPitagoriques n = [(i, j, k) | i <- [1..n], j <- [i..n], k <- [j..n], i*i + j*j = k*k]
  -- gens eficient, però per què es vegi com usar


-- (prodCart sense llistes per comprensió)

prodCart n = concatMap (f n) [1..n]     -- concatMap vé a ser concat . map
f n i = zip (repeat i) [1..n]

-- o

prodCart n = concatMap (\i -> zip (repeat i) [1..n]) [1..n]