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[1,2,3].map(x => x + 1)

[1,2,3].flatMap(x => [x + 1])

[1,2,3].map(a => a + 1).filter(b => b != 3)

[1,2,3].flatMap(a => [a + 1]).flatMap(b => b != 3 ? [b] : [])

[1,2,3].flatMap(a => [a + 1].flatMap(b => b != 3 ? [b] : []))

[1,2,3] >>= \a -> [a+1] >>= \b -> if b == 3 then [] else [b] 

do 
 a <- [1,2,3] 
 b <- [a+1] 
 if b == 3 then [] else [b] 

streetName = getStreetName (getAddress (getUser 17)) 

case getUser 17 of
 Nothing -> Nothing 
 Just user ->
 case getAddress user of
 Nothing -> Nothing 
 Just address ->
 getStreetName address

do
 user <- getUser 17
 addr <- getAddress user
 getStreetName addr

add2 :: State Integer Integer
add2 = do
 -- add 1 to state
 x <- get
 put (x + 1)
 -- increment in another way
 modify (+1)
 -- return state
 get
evalState add2 7
=> 9

main :: IO ()
main = do 
 putStrLn "Hello World"

main = do
 putStrLn "What is your name?"
 name <- getLine
 putStrLn ("hello" ++ name)

[1,2,3].map(x => x + 1)

[1,2,3].flatMap(x => [x + 1])

[1,2,3].map(a => a + 1).filter(b => b != 3)

[1,2,3].flatMap(a => [a + 1]).flatMap(b => b != 3 ? [b] : [])

[1,2,3].flatMap(a => [a + 1].flatMap(b => b != 3 ? [b] : []))

[1,2,3] >>= \a -> [a+1] >>= \b -> if b == 3 then [] else [b] 

do 
 a <- [1,2,3] 
 b <- [a+1] 
 if b == 3 then [] else [b] 

streetName = getStreetName (getAddress (getUser 17)) 

case getUser 17 of
 Nothing -> Nothing 
 Just user ->
 case getAddress user of
 Nothing -> Nothing 
 Just address ->
 getStreetName address

do
 user <- getUser 17
 addr <- getAddress user
 getStreetName addr

add2 :: State Integer Integer
add2 = do
 -- add 1 to state
 x <- get
 put (x + 1)
 -- increment in another way
 modify (+1)
 -- return state
 get
evalState add2 7
=> 9

main :: IO ()
main = do 
 putStrLn "Hello World"

main = do
 putStrLn "What is your name?"
 name <- getLine
 putStrLn ("hello" ++ name)

Like any other practical language, Haskell has a bunch of built-in functions which interface with the outside world: putStrLine, readLine and so on. These functions are called "impure" because they either cause side effects or have non-deterministic results. Even something simple like getting the time is considered impure because the result is non-deterministic – calling it twice with the same arguments may return different values.

Like any other practical language, Haskell has a bunch of built-in functions which interface with the outside world: putStrLn, getLine and so on. These functions are called "impure" because they either cause side effects or have non-deterministic results. Even something simple like getting the time is considered impure because the result is non-deterministic – calling it twice with the same arguments may return different values.

do a <- [1,2,3] 
 b <- [a+1] 
 if b == 3 then [] else [b] 

main = do
 putStrLn "What is your name?"
 name <- getLine
 putStrLn "hello" ++ name

do a <- [1,2,3] 
 b <- [a+1] 
 if b == 3 then [] else [b] 

main = do
 putStrLn "What is your name?"
 name <- getLine
 putStrLn ("hello" ++ name)