Erlang学习六

水深无声 2022-08-14 00:44 169阅读 0赞

**字符串：**

在erlang中字符串就是一个整数列表。

![20141114135557500][]

**模块：**

-module(tut).
 -export([getnum/1]).
 
 getnum(N) ->
 	tut4:getnum(N).<pre name="code" class="plain">

-module(tut4).
 -export([getnum/1]).
 
 
 getnum(Name) ->
 	case Name of
 		a -> 1;
 		b -> 2
 	end.

**fun使用:**

![20141114151951530][]

![20141114152601313][]

![20141114160350228][]

-module(tut).
 -export([for/3]).
 
 
 for(Max,Max,F) ->
 	[F(Max)];
 
 for(I,Max,F) ->
 	[F(I) | for(I + 1,Max,F)].<pre name="code" class="plain">

41> c(tut).
 {ok,tut}
 42> tut:for(1,5,fun(I) -> 2*I end).
 [2,4,6,8,10]

-module(tut).
 -export([sum/1]).
 
 
 sum([]) ->
 	0;
 
 sum([Head | Rest]) ->
 	Head + sum(Rest).
 
 
 44> c(tut).
 {ok,tut}
 45> tut:sum([1,2,3]).
 6
 46>

-module(tut).
 -export([map/2]).
 
 
 map(_,[]) ->
 	[];
 
 map(F,[Head | Rest]) ->
 	[F(Head) | map(F,Rest)].
 
 
 
 
 48> c(tut).
 {ok,tut}
 49> tut:map(fun(I) I*2 end,[1,2,3]).
 * 1: syntax error before: I
 49> tut:map(fun(I)-> I*2 end,[1,2,3]).
 [2,4,6]
 50>

-module(tut).
 -export([total/1]).
 -import(lists,[sum/1,map/2]).
 
 total(L) ->
 	sum( map(fun(I) -> I*2 end,L) ).
 
 
 
 55> c(tut).
 {ok,tut}
 56> tut:total([1,2,3]).
 12
 57>

**列表解析：**

-module(tut).
 -export([map/2]).
 
 map(F,L) ->
 	[F(X) || X <- L].

快速排序：

-module(tut).
 -export([sort/1]).
 
 
 sort([]) ->
 	[];
 
 
 sort([Head | Rest]) ->
 	sort([X || X <- Rest,X < Head])
 	++ [Head] ++
 	sort([X || X <- Rest,X >= Head]).
 
 
 68> c(tut).
 {ok,tut}
 69> tut:sort([22,1,34,2,5,3,22]).
 [1,2,3,5,22,22,34]
 70>

毕达哥拉斯三元组：

-module(tut).
 -export([pythag/1]).
 
 
 pythag(N) ->
 	[{A,B,C} || A <- lists:seq(1,N),
 				B <- lists:seq(1,N),
 				C <- lists:seq(1,N),
 				A + B + C =< N,
 				A * A + B*B =:= C * C].
 
 
 
 
 74> c(tut). 
 {ok,tut}
 75> tut:pythag(16).
 [{3,4,5},{4,3,5}]
 76>

变位词：

-module(tut).
 -export([test/1]).
 
 test([]) ->
 	[[]];
 
 test(L) ->
 	[ [H | R] || H <- L,R <- test(L -- [H])].
 
 
 84> c(tut). 
 {ok,tut}
 85> tut:test("abc").
 ["abc","acb","bac","bca","cab","cba"]
 86>

断言：

-module(tut).
    -export([max/2]).
    
    max(X,Y) when X > Y -> X;
    
    max(_,Y) -> Y.
    
    
    88> c(tut).
    {ok,tut}
    89> tut:max(1,2).
    2
    90>

test(X,Y) when is_integer(X),X > Y,Y < 6 ->
 	Y.

**Record:**

默认字段有默认值；

-record(stu,{name = joe,age = 20,text}).
 
 
 93> rr("rec.hrl").
 [stu]
 94> X = #stu{}.
 #stu{name = joe,age = 20,text = undefined}
 95> Y = #stu{age = 21}.
 #stu{name = joe,age = 21,text = undefined}
 96> Z = Y#stu{}.
 #stu{name = joe,age = 21,text = undefined}
 97> <pre name="code" class="plain">97> #stu{name = N} = Z. 
 #stu{name = joe,age = 21,text = undefined}
 98> N.
 joe
 99> Z#stu.name.
 joe
 100>

[20141114135557500]: /images/20220810/961450de33654350bdb164f0cd7abd80.png
[20141114151951530]: /images/20220810/75d379b6c269450fb2a02be9e01f8bb7.png
[20141114152601313]: /images/20220810/055d877a8c08468da681a9cd067bc8bd.png
[20141114160350228]: /images/20220810/34c87d3da5424b04b30daf30fd2deea0.png