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λ> :k Maybe
Maybe :: * -> *
λ> :k Eq
Eq :: * -> Constraint
λ> :k Countable
Countable :: (* -> *) -> Constraint
λ> :k []
[] :: * -> *
λ> :k ([] Int)
([] Int) :: *
λ> :k [Int]
[Int] :: *
λ> :t length
length :: Foldable t => t a -> Int
λ> count [1..10]
10
λ> count Data.t
3
λ> count tree
5
λ> elements Data.t
[3,1,5]
λ> elements Data.t
[1,3,5]
λ> elements Data.tree
[1,2,3,4,5]
λ> fmap (+2) [1..10]
[3,4,5,6,7,8,9,10,11,12]
λ> fmap (+2) t
Node {root = 5, left = Node {root = 3, left = Empty, right = Empty}, right = Node {root = 7, left = Empty, right = Empty}}
λ> fmap (+2) tree
Tree {val = 3, subtrees = SubTree {firstTree = Tree {val = 4, subtrees = None}, restTrees = SubTree {firstTree = Tree {val = 5, subtrees = SubTree {firstTree = Tree {val = 6, subtrees = None}, restTrees = None}}, restTrees = SubTree {firstTree = Tree {val = 7, subtrees = None}, restTrees = None}}}}
λ> (+2) <$> [1..10]
[3,4,5,6,7,8,9,10,11,12]
λ> (+2) <$> Data.t
Node {root = 5, left = Node {root = 3, left = Empty, right = Empty}, right = Node {root = 7, left = Empty, right = Empty}}
λ> (+2) <$> Data.tree
Tree {val = 3, subtrees = SubTree {firstTree = Tree {val = 4, subtrees = None}, restTrees = SubTree {firstTree = Tree {val = 5, subtrees = SubTree {firstTree = Tree {val = 6, subtrees = None}, restTrees = None}}, restTrees = SubTree {firstTree = Tree {val = 7, subtrees = None}, restTrees = None}}}}
λ> (+2) $ 5
7
λ> (+2) <$> (Just 5)
Just 7
λ> (+2) <$> Nothing
Nothing
λ> :k Either
Either :: * -> * -> *
λ> (+2) <$> (Left 5)
Left 5
λ> (+2) <$> (Right 5)
Right 7
λ> :t (,)
(,) :: a -> b -> (a, b)
λ> :k (,)
(,) :: * -> * -> *
λ> (+2) <$> (5, 7)
(5,9)
λ> :k (->)
(->) :: TYPE q -> TYPE r -> *
λ> :k ((->) Int String)
((->) Int String) :: *
λ> :k (Int -> String)
(Int -> String) :: *
λ> (+2) <$> (*3)
(+2) <$> (*3) :: Num b => b -> b
λ> (+2) <$> (*3) $ 5
17
λ> (+2) <$> getInt
5
7
λ> getLine
asdsa
"asdsa"
λ> ("Hello " ++) <$> getLine
Trifon
"Hello Trifon"
λ> :t (*>)
(*>) :: Applicative f => f a -> f b -> f b
λ> (+2) <$> Just 100
Nothing
λ> (+) <$> Just 2 <*> Just 3
Just 5
λ> (+) <$> Nothing <*> Just 3
Nothing
λ> (+) <$> Just 2 <*> Nothing
Nothing
λ> (+) <$> Right 2 <*> Right 3
Right 5
λ> (+) <$> Right 2 <*> Left "abc"
Left "abc"
λ> (+) <$> Left "error" <*> Right 3
Left "error"
λ> (+) <$> Right 2 <*> Left "erro"
Left "erro"
λ> (+) <$> [1,3,5] <*> [2,4,6]
[3,5,7,5,7,9,7,9,11]
λ> (^3) <$> ((+) <$> [1,3,5] <*> [2,4,6])
[27,125,343,125,343,729,343,729,1331]
λ> ZipList [1..5]
ZipList [1..5] :: (Enum a, Num a) => ZipList a
λ> getZipList (ZipList [1..5])
[1,2,3,4,5]
λ> (+) <$> ZipList [1,3,5] <*> ZipList [2,4,6]
(+) <$> ZipList [1,3,5] <*> ZipList [2,4,6] :: Num b => ZipList b
λ> (+) <$> ZipList [1,3,5] <*> ZipList [2,4,6]
ZipList {getZipList = [3,7,11]}
λ> const 2 3
2
λ> (+) <$> (*3) <*> (*5) $ 2
16
λ> (+) <$> getInt <*> getInt
5
8
13
λ> liftA2 (+) getInt getInt
5
8
13
λ> sequenceA [Just 2, Just 3, Just 5]
Just [2,3,5]
λ> sequenceA [Just 2, Nothing, Just 5]
Nothing
λ> sequenceA [(+2), (*3), (+5)]
sequenceA [(+2), (*3), (+5)] :: Num a => a -> [a]
λ> sequenceA [(+2), (*3), (+5)] 1
[3,3,6]
λ> sequenceA [(+2), (*3), (+5)] 1
[3,3,6]
λ> :i IO
newtype IO a
  = GHC.Types.IO (GHC.Prim.State# GHC.Prim.RealWorld
                  -> (# GHC.Prim.State# GHC.Prim.RealWorld, a #))
  	-- Defined in ‘GHC.Types’
instance Applicative IO -- Defined in ‘GHC.Base’
instance Functor IO -- Defined in ‘GHC.Base’
instance Monad IO -- Defined in ‘GHC.Base’
instance MonadPlus IO -- Defined in ‘GHC.Base’
instance Monoid a => Monoid (IO a) -- Defined in ‘GHC.Base’
λ> Just 3 >>= getAt' [1..5]
Just 4
λ> Just 10 >>= getAt' [1..5]
Nothing
λ> [1..5] >>= (\x -> [-1..x])
[-1,0,1,-1,0,1,2,-1,0,1,2,3,-1,0,1,2,3,4,-1,0,1,2,3,4,5]
λ> do x <- [1..5]; return [-1..x]
[[-1,0,1],[-1,0,1,2],[-1,0,1,2,3],[-1,0,1,2,3,4],[-1,0,1,2,3,4,5]]
λ> do x <- [1..5]; [-1..x]
[-1,0,1,-1,0,1,2,-1,0,1,2,3,-1,0,1,2,3,4,-1,0,1,2,3,4,5]
λ> do x <- [1..5]; y <- [-1..x]; return y
[-1,0,1,-1,0,1,2,-1,0,1,2,3,-1,0,1,2,3,4,-1,0,1,2,3,4,5]
λ> [ y |  x <- [1..5], y <- [-1..x] ]
[-1,0,1,-1,0,1,2,-1,0,1,2,3,-1,0,1,2,3,4,-1,0,1,2,3,4,5]
λ> (+2) >>= (\x -> (*x)) $ 3
15
λ> (+2) >>= (\x -> (*x)) $ 10
120
λ>