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           example codes  for Haskell, a functional language
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                       ----  list  ----

Main> length [0,1,2,3]                   +---------------------------------+  
4                                        | length [] = 0                   |
Main> length ['a', 'b']                  | length (x:xs) = 1 + length xs   |
2                                        +---------------------------------+
Main> length [[1,2], [2,3,4,5], [7,8]]
3
Main> 

                ---- list comprehension ----
      +----------------------------------------------------------+
      | qsort [] = []                                            |
      | qsort (x:xs) = qsort(left) ++ [x] ++ qsort(right) where  |
      |   left = [ y | y <- xs, y < x ]                          |
      |   right = [ z | z <- xs, z >= x ]                        |
      +----------------------------------------------------------+

Main> [ x+1 | x <- [1,2,3,4,5] ]
[2,3,4,5,6]
Main> [ x | x <- [1,2,3,4,5], x > 3 ]
[4,5]
Main> qsort [44, 22, 1, 101, 23]
[1,22,23,44,101]
Main> 

                ---- higher order function ----

Main> map addone [1,2,3,4,5]            +---------------------------+        
[2,3,4,5,6]                             | addone x = x + 1          |
Main> alladdone [1,2,3,4,5]             | alladdone = map addone    |
[2,3,4,5,6]                             | sum = foldr (+) 0         |
Main> map (+ 4) [1,2,3,4,5]             +---------------------------+
[5,6,7,8,9]
Main> map (* 2) [1,2,3,4,5]
[2,4,6,8,10]
Main> foldr (+) 0 [1,2,3,4,5,6]
21
Main> sum [1,2,3,4,5,6]
21
Main> 


           ---- infinite list, lazy evaluation  ----

Main> take 3 n                             +---------------------------+
[1,2,3]                                    | from n = n : from(n + 1)  |
Main> sum (take 100 n)                     | n = from 1                |
5050                                       +---------------------------+
Main>