• 见《Haskell Platform安装过程》

• 代码

-- helloWorld.hs
-- 定义名为hi的函数
hi = "hello, world!"

• 运行

$ ghci
GHCi, version 7.4.1: http://www.haskell.org/ghc/  :? for help
Loading package ghc-prim ... linking ... done.
Loading package integer-gmp ... linking ... done.
Loading package base ... linking ... done.
ghci>:l helloWorld.hs
[1 of 1] Compiling Main             ( helloWorld.hs, interpreted )
Ok, modules loaded: Main.
ghci>hi
"hello, world!"

-- function.hs
doubleMe x = x + x
doubleUs x y = doubleMe x + doubleMe y

ghci>:l function.hs
[1 of 1] Compiling Main             ( function.hs, interpreted )
Ok, modules loaded: Main.
ghci>doubleMe 2
4
ghci>doubleUs 3 4
14

• if语句

maxNumber x y = if x > y then xelse y

ghci>:l baseStruc.hs
[1 of 1] Compiling Main             ( baseStruc.hs, interpreted )
Ok, modules loaded: Main.
ghci>maxNumber 3 5
5
ghci>maxNumber 5 3
5

• case语句

isLucky x = case x of 1 -> "1:lucky"2 -> "2:No lucky"otherwise -> "lucky"

ghci>isLucky 1
"1:lucky"
ghci>isLucky 2
"2:No lucky"
ghci>isLucky 3
"lucky"
ghci>isLucky 4
"lucky"

• let语句

doubleSum x y =let doublex = 2 * xdoubley = 2 * yin doublex + doubley

ghci>doubleSum 3 4
14
ghci>doubleSum 1 2
6

• where语句

doubleSum2 x y = doublex + doubleywhere doublex = 2 * xdoubley = 2 * y

ghci>doubleSum2 1 2
6
ghci>doubleSum2 2 3
10

• 模式匹配(Pattern Matching)

例1

lucky 7 = "You are lucky"
lucky x = "Sorry, you are not lucky"

ghci>lucky 7
"You are lucky"
ghci>lucky 1
"Sorry, you are not lucky"
ghci>lucky 2
"Sorry, you are not lucky"

例2

foo 0 x = (-1) * x
foo 1 x = x
foo x y = 0

ghci>foo 1 2
2
ghci>foo 2 3
0
ghci>foo 3 4
0
ghci>foo 0 2
-2

例3

foo' 0 x = (-1) * x
foo' x y = 0
foo' 1 x = x

ghci>foo' 1 2
0
ghci>foo' 1 3
0
ghci>foo' 2 3
0
ghci>foo' 3 4
0
ghci>foo' 0 2
-2

• 门卫(Guard)

例1

mdivide x y| y == 0 = "Can not divide"| x / y > 10 = "first number is larger than the second number"| x / y < 1  = "first number is less than the second number"| otherwise = "almost equal"

ghci>mdivide 3 0
"Can not divide"
ghci>mdivide 3 2
"almost equal"
ghci>mdivide 30 2
"first number is larger than the second number"
ghci>mdivide 3 5
"first number is less than the second number"

例2

mdivide' x y| x / y > 10 = "first number is larger than the second number"| y == 0 = "Can not divide"| x / y < 1  = "first number is less than the second number"| otherwise = "almost equal"

ghci>mdivide' 3 0
"first number is larger than the second number"
ghci>mdivide' 3 1
"almost equal"
ghci>mdivide' 30 3
"almost equal"
ghci>mdivide' 30 2
"first number is larger than the second number"
ghci>mdivide' 2 3
"first number is less than the second number"

• 递归(Recursion)

注：理解门卫与递归如何结合在一起工作

msum x y| x > y = msum y x| x == y = x| otherwise = x + msum (x+1) y

ghci>msum 1 100
5050
ghci>msum 2 4
9
ghci>msum 100 1
5050