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• • some math-oriented examples from the Hugs distibution • type classes used to capture lattices abstractly (from the Hugs distibution) • a generic sorting application applied to a simple database • a flexible system for parsing and processing arithmetic expressions
Booleans and if expressions
> if 3 < 2 then "oops" else "hurray!"
"hurray!"
> (if 3 < 2 then (+) else (*)) 10 20
200
Booleans and if expressions
Infinite lists and lazy evaluation
> [1,3..]
[1,3,5,7,9,11,13,15,17,19,21,23,25,27,29,31,33,{Interrupted!}
> take 20 [1,3..]
[1,3,5,7,9,11,13,15,17,19,21,23,25,27,29,31,33,35,37,39]
Booleans and if expressions
Infinite lists and lazy evaluation
Higher-order functions
> even 3
False
> any even [1,3..11]
False
> any (>10) [1..]
True
Booleans and if expressions
Infinite lists and lazy evaluation
Higher-order functions
Currying
> 2 + 3
5
> (+) 2 3
5
> :t (+)
(+) :: Num a => a -> a -> a
> :t (2+)
(2 +) :: Num a => a -> a
Booleans and if expressions
Infinite lists and lazy evaluation
Higher-order functions
Currying
The map functional
> map (^2) [1..10]
[1,4,9,16,25,36,49,64,81,100]
> map (`div` 3) [1..20]
[0,0,1,1,1,2,2,2,3,3,3,4,4,4,5,5,5,6,6,6]
> map reverse ["hey", "there", "world"]
["yeh","ereht","dlrow"]
Booleans and if expressions
Infinite lists and lazy evaluation
Higher-order functions
Currying
The map functional
The fold functions
> foldr (+) 0 [1..10]
55
> sum [1..10]
55
> foldr (*) 1 [1..5] == 1 * 2 * 3 * 4 * 5 * 1
True
> foldr (++) [] ["a", "bb", "ccc"]
"abbccc"
Booleans and if expressions
Infinite lists and lazy evaluation
Higher-order functions
Currying
The map functional
The fold functions
Strong, static typing
> :t ['a'..'z']
enumFromTo 'a' 'z' :: [Char]
> :t reverse
reverse :: [a] -> [a]
> :t foldr
foldr :: (a -> b -> b) -> b -> [a] -> b
> :t foldr (++) []
foldr (++) [] :: [[a]] -> [a]
Booleans and if expressions
Infinite lists and lazy evaluation
Higher-order functions
Currying
The map functional
The fold functions
Strong, static typing
More examples of Haskell in actions