December 2015 1HaskellADay 1-Liners

One-liners

• December 30th, 2015: You have a string of 'digits' in base whatever to convert to an Int
  debase :: [Int] -> Int -> Int
  debase [12,21,3] 26 ~> 8661
  Define debase
• Gautier DI FOLCO @gautier_difolco
  import Data.Bifunctor
  debase = curry (sum . uncurry (zipWith (*)) . bimap reverse (flip iterate 1 . (*)))
• bazzargh @bazzargh
  debase a b = sum $ zipWith (*) (reverse a) (map (b^) [0..])
• obadz @obadzz
  or debase l b = foldl (\ p n -> p * b + n) 0 l
• bazzargh @bazzargh
  that's better than mine. how about:
  flip (foldl1 . ((+) .) . (*))
• December 12th, 2015: #math You have this sequence: [1,1,1,1,1,1,2,1,1,1,3,3] What is this pattern? Is there one? Write #haskell to generate this list.
• December 3rd, 2015: Lens-y again Points-free-itize the following correctName :: Row -> Row correctName r = set lastName (init (view lastName r)) r
• December 3rd, 2015: Let's get a little lens-y with this one: accumer :: Getter a t a -> t -> [a] -> [a] accumer f s acc = ans where ans = view f s:acc
• Define the curried-accumer function that curries away the acc-argument.
• What would the curried definition be if the function type were: accumer :: Getter a t a -> t -> Set a -> Set a
• December 3rd, 2015: define minimax :: Ord eh => eh -> (eh, eh) -> (eh, eh) such that, e.g.: minimax 1 (2,3) ~> (1,3) minimax 10 (2,3) ~> (2,10)
• Thomas Dietert @thomasdietert In that case, minimax n (x,y) = (minimum [n,x,y], maximum [n,x,y])
• joomy @cattheory minimax = liftM2 (***) min max
• December 1st, 2015: define (->>) :: (a -> m ()) -> (a -> m ()) -> a -> m () All monadic effects must be evaluated.
• Jérôme @phollow (->>) f g a = f a >> g a 
• then liftM2 (>>)
• Nicoλas @BeRewt but the full applicative is: liftA2 (*>)