some simple arithmetic



In [1]:

    
2 + 15



In [2]:

    
49 * 100



In [3]:

    
1892 - 1472



In [4]:

    
5 /2

2.5



In [5]:

    
(50 * 100) - 499



In [6]:

    
50 * 100 - 599



In [7]:

    
50 * ( 100 - 499)



In [8]:

    
-- 5 * -3 will raise
5 * (-3)

-15

some boolean



In [9]:

    
True && False









    




Evaluate
Found:
True && False
Why Not:
False






    





False



In [10]:

    
True && True









    




Evaluate
Found:
True && True
Why Not:
True






    





True



In [11]:

    
False || True









    




Evaluate
Found:
False || True
Why Not:
True






    





True



In [12]:

    
not False









    




Evaluate
Found:
not False
Why Not:
True






    





True



In [13]:

    
not (True && True)









    




Evaluate
Found:
True && True
Why Not:
True






    





False



In [14]:

    
5 == 5









    





True



In [15]:

    
1 == 0









    





False



In [16]:

    
5 /= 5 -- not equal









    





False



In [17]:

    
5 /= 4









    





True



In [18]:

    
"hello" == "hello"









    





True



In [19]:

    
-- strong type language
-- this would raise: 5 + "hello" or 5 == True

some functions



In [20]:

    
-- 函数通常使用前缀调用方式.
succ 8



In [21]:

    
min 9 10



In [22]:

    
min 3.4 3.2

3.2



In [23]:

    
max 100 101



In [24]:

    
-- 函数调用有着最高的优先级
succ 9 + max 5 4 + 1
(succ 9) + (max 5 4) + 1









    




Redundant bracket
Found:
(succ 9) + (max 5 4)
Why Not:
succ 9 + (max 5 4)
Redundant bracket
Found:
(succ 9) + (max 5 4)
Why Not:
(succ 9) + max 5 4






    





16






    





16



In [25]:

    
--the following was not equal
succ 9 * 10
succ (9 * 10)



In [26]:

    
-- 如果函数接受两个参数，可以中坠调用方式
div 92 10
92 `div` 10

define function



In [27]:

    
doubleMe x = x + x



In [28]:

    
-- save the follow to `baby.hs` file.
-- in the ghci, use `:l baby`. 
-- then we can use double function
-- doubleMe 9
-- doubleMe 8.3



In [29]:

    
doubleUs x y = x*2 + y*2



In [30]:

    
doubleUs x y = doubleMe x + doubleMe y



In [31]:

    
-- function with if/else.
-- haskell中if后的else为必须。
doubleSmallNumber x = if x > 100
    then x
    else x * 2



In [32]:

    
-- if是一个表达式,使用一个'后缀来定义一个新的但是差别比较小的函数
doubleSmallNumber' x = (if x > 100 then x else x*2) + 1



In [33]:

    
-- 函数不能以大写字母开头
-- 没有参数的函数被称为定义或名字
conanO'Brien = "It's a-me, Conan O'Brien!"









    




Use camelCase
Found:
conanO'Brien = ...
Why Not:
conanOBrien = ...



In [34]:

    
let lostNumbers = [4, 8, 15, 16, 23, 42]
lostNumbers









    





[4,8,15,16,23,42]



In [35]:

    
[1, 2, 3, 4] ++ [9, 10, 11, 12]









    





[1,2,3,4,9,10,11,12]



In [37]:

    
"hello" ++ " " ++ "world"









    





"hello world"



In [38]:

    
-- 单引号为字符，双引号为字符串
'A': " Small CAT"









    





"A Small CAT"



In [39]:

    
5:[1,2,3,4,5]









    





[5,1,2,3,4,5]



In [40]:

    
-- 列表智能防同一类内容
[1,2,3,4,5] ++ []









    





[1,2,3,4,5]



In [41]:

    
-- 列表索引使用 !! 操作符
"Steve Buscemi" !! 6

'B'



In [42]:

    
[9.4, 33.2, 98.2, 11.2, 23.21] !! 1



In [43]:

    
-- 嵌套列表长度可以不同，但类型必须一样
let b = [[1,2,3,4], [5,3,3,3],[1,2,3,4,5], [1,2,3]]
b









    





[[1,2,3,4],[5,3,3,3],[1,2,3,4,5],[1,2,3]]



In [44]:

    
b ++ [[1,1,1,1]]









    





[[1,2,3,4],[5,3,3,3],[1,2,3,4,5],[1,2,3],[1,1,1,1]]



In [45]:

    
[6,6,6]:b









    





[[6,6,6],[1,2,3,4],[5,3,3,3],[1,2,3,4,5],[1,2,3]]



In [46]:

    
b !! 2









    





[1,2,3,4,5]



In [47]:

    
-- 列表是可以比较的，按顺序比较列表内元素
[3,2,1] > [2, 1, 0]









    





True



In [48]:

    
[3,2,1] > [2, 10, 100]









    





True



In [49]:

    
[3,4,2] > [3,4,3]









    





False



In [50]:

    
[3,4,2] == [3,4,2]









    





True



In [51]:

    
-- 更多列表操作
head [5, 4, 3, 2, 1]



In [52]:

    
tail [5, 4, 3, 2, 1]









    





[4,3,2,1]



In [53]:

    
last [5, 4, 3, 2, 1]



In [54]:

    
init [5, 4, 3, 2, 1]









    





[5,4,3,2]



In [55]:

    
-- this would raise
-- head []



In [56]:

    
length [5, 4, 3, 2, 1]



In [57]:

    
-- if null
null [1, 2, 3]









    





False



In [58]:

    
null []









    




Evaluate
Found:
null []
Why Not:
True






    





True



In [59]:

    
reverse [5 ,4, 3, 2, 1]









    





[1,2,3,4,5]



In [60]:

    
take 3 [5,4,3,2,1]









    





[5,4,3]



In [61]:

    
take 1 [3, 9, 3]

[3]



In [62]:

    
take 5 [1, 2]



In [63]:

    
take 0 [6, 6, 6]









    




Take on a non-positive
Found:
take 0 [6, 6, 6]
Why Not:
[]






    





[]



In [64]:

    
drop 3 [8,4, 2, 15,6]



In [65]:

    
drop 0 [1,2,3,4]









    





[1,2,3,4]



In [66]:

    
drop 100 [1,2,3,4]

[]



In [67]:

    
maximum [1,9,2,3,4]



In [68]:

    
minimum [8,4,2,1,5,6]



In [69]:

    
sum [5,2,1,6,3,2,5,7]



In [70]:

    
product [6,2,1,2]



In [71]:

    
product [1,2,5,6,7,9,3,0]



In [72]:

    
-- 使用 `` 把前缀函数变成后缀函数
4 `elem` [3,4,5,6]
10 `elem` [3,4,5,6]









    





True






    





False



In [73]:

    
--  区间
[1..20]









    





[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20]



In [74]:

    
['a'..'z']









    





"abcdefghijklmnopqrstuvwxyz"



In [76]:

    
['K'..'Z']









    





"KLMNOPQRSTUVWXYZ"



In [77]:

    
[2,4..20]









    





[2,4,6,8,10,12,14,16,18,20]



In [78]:

    
[3,6..20]









    





[3,6,9,12,15,18]



In [79]:

    
[13,26..24*13]









    





[13,26,39,52,65,78,91,104,117,130,143,156,169,182,195,208,221,234,247,260,273,286,299,312]



In [80]:

    
-- haskell是惰性执行的。随你可以创建一个无线区间，在需要时取相应长度的数
take 24 [13,26..]









    





[13,26,39,52,65,78,91,104,117,130,143,156,169,182,195,208,221,234,247,260,273,286,299,312]



In [81]:

    
-- cycle/repeat/replicate用来创建无限列表
take 10 (cycle [1,2,3])









    





[1,2,3,1,2,3,1,2,3,1]



In [82]:

    
take 10 (cycle "LOL ")









    





"LOL LOL LO"



In [83]:

    
take 10 (repeat 5)









    




Use replicate
Found:
take 10 (repeat 5)
Why Not:
replicate 10 5






    





[5,5,5,5,5,5,5,5,5,5]



In [84]:

    
replicate 3 10



In [85]:

    
-- haskell浮点数时不准确的
[0.1,0.3..1]









    





[0.1,0.3,0.5,0.7,0.8999999999999999,1.0999999999999999]



In [86]:

    
-- 列表推导
[x*2 | x <- [1..10]]









    





[2,4,6,8,10,12,14,16,18,20]



In [87]:

    
[x*2 | x <- [1..10], x*2 >= 12]









    





[12,14,16,18,20]



In [88]:

    
[x | x <- [50..100], x `mod` 7 == 3]









    





[52,59,66,73,80,87,94]



In [90]:

    
let booBangs xs = [if x < 10 then "BOOM!" else "BANG!" | x <- xs, odd x]



In [91]:

    
booBangs [7..13]









    





["BOOM!","BOOM!","BANG!","BANG!"]



In [92]:

    
[x | x <- [10..20], x /= 13, x/=15, x/=19]









    





[10,11,12,14,16,17,18,20]



In [93]:

    
[x + y | x <- [1,2,3], y <- [10, 100, 1000]]









    





[11,101,1001,12,102,1002,13,103,1003]



In [94]:

    
[x + y | x <- [1,2,3], y <- [10, 100, 1000, 10]]









    





[11,101,1001,11,12,102,1002,12,13,103,1003,13]



In [95]:

    
[x*y | x <- [2,5,10], y <- [8,10,11], x*y > 50]









    





[55,80,100,110]



In [97]:

    
-- 通过列表推导编写length函数;
let length' xs = sum [1 | _ <- xs]



In [99]:

    
let removeNonUppercase st = [c | c <- st, c `elem` ['A'..'Z']]



In [100]:

    
-- 元组是固定长度的可异构的集合
(1, 3)



In [101]:

    
(3, 'a', "hello")









    





(3,'a',"hello")



In [102]:

    
-- 长度为2的元组又叫序对,长度为3的叫triple
-- 不同长度的元组是不同类型
-- 不能创建单元素列表



In [104]:

    
-- 使用pair
fst (3, 1)



In [105]:

    
fst ("wow", False)









    





"wow"



In [106]:

    
snd (8, 11)



In [107]:

    
snd ("wow", False)









    




Evaluate
Found:
snd ("wow", False)
Why Not:
False






    





False



In [108]:

    
zip [1, 2, 3, 4] [5,5,5,5,5]









    





[(1,5),(2,5),(3,5),(4,5)]



In [110]:

    
let rightTriangle = [(a, b, c) | c <- [1..10], a <- [1..c], b <- [1..c], a^2 + b^2 == c^2, a+ b+ c == 24]



In [111]:

    
rightTriangle









    





[(6,8,10),(8,6,10)]



In [ ]: