$ ghci 
GHCi, version 8.8.4: https://www.haskell.org/ghc/  :? for help
Prelude> :q 
Leaving GHCi.
$ ghci 
GHCi, version 8.8.4: https://www.haskell.org/ghc/  :? for help
Prelude> :l lec1.hs 
[1 of 1] Compiling Main             ( lec1.hs, interpreted )
Ok, one module loaded.
*Main> :r 
[1 of 1] Compiling Main             ( lec1.hs, interpreted )
Ok, one module loaded.
*Main> main 
"hello world!"
*Main> :q
Leaving GHCi.
frankfu:~/teaching/544/spring-2026/lectures/lecture1$ ghc lec1.hs
[1 of 1] Compiling Main             ( lec1.hs, lec1.o )
Linking lec1 ...
frankfu:~/teaching/544/spring-2026/lectures/lecture1$ ls
lec1  lec1.hi  lec1.hs  lec1.hs~  lec1.o  lec1Prep.hs  lec1Prep.hs~
frankfu:~/teaching/544/spring-2026/lectures/lecture1$ ./lec1 
"hello world!"
frankfu:~/teaching/544/spring-2026/lectures/lecture1$ ghci 
GHCi, version 8.8.4: https://www.haskell.org/ghc/  :? for help
Prelude> :l lec1.hs 
[1 of 1] Compiling Main             ( lec1.hs, interpreted )
Ok, one module loaded.
*Main> b 
True
*Main> :t b 
b :: Bool
*Main> True && False 
False
*Main> True || False 
True
*Main> 1 + 2 + (3 * 4)
15
*Main> :t 1 
1 :: Num p => p
*Main> :t fst 
fst :: (a, b) -> a
*Main> :t snd
snd :: (a, b) -> b
*Main> :r
[1 of 1] Compiling Main             ( lec1.hs, interpreted )
Ok, one module loaded.
*Main> fst p1 
2
*Main> snd p2 
'a'
*Main> :t fst p1
fst p1 :: Int
*Main> :t fst p2
fst p2 :: Int
*Main> :t snd p2
snd p2 :: Char
*Main> :t snd p1
snd p1 :: Bool
*Main> :t (7, 'b')
(7, 'b') :: Num a => (a, Char)
*Main> :t (7, True, 'b')
(7, True, 'b') :: Num a => (a, Bool, Char)
*Main> :t (True, 'b', 7)
(True, 'b', 7) :: Num c => (Bool, Char, c)
*Main> :t ()
() :: ()
*Main> :t (True)
(True) :: Bool
*Main> :t [1,2,3]
[1,2,3] :: Num a => [a]
*Main> :t [True, False, True]
[True, False, True] :: [Bool]
*Main> :t ['a', True]

<interactive>:1:7: error:
    • Couldn't match expected type ‘Char’ with actual type ‘Bool’
    • In the expression: True
      In the expression: ['a', True]
*Main> :t [] 
[] :: [a]
*Main> :t (:) 
(:) :: a -> [a] -> [a]
*Main> 
*Main> 
*Main> 1:[] 
[1]
*Main> 
*Main> 
*Main> 
*Main> 
*Main> 1:(2:(3:[]))
[1,2,3]
*Main> 'b' :('c':[])
"bc"  --- ['b', 'c']
*Main> :t "bc"
"bc" :: [Char]
*Main> :r
[1 of 1] Compiling Main             ( lec1.hs, interpreted )
Ok, one module loaded.
*Main> :r
[1 of 1] Compiling Main             ( lec1.hs, interpreted )
Ok, one module loaded.
*Main> :t l2
l2 :: ([Int], String)
*Main> l2
([1,2,3],"hello")
*Main> :r
[1 of 1] Compiling Main             ( lec1.hs, interpreted )
Ok, one module loaded.
*Main> :t l2
l2 :: ([Int], [Char])