Erlang学习六

字符串：

在erlang中字符串就是一个整数列表。

模块：

<span style="font-size:18px;">-module(tut).
-export([getnum/1]).

getnum(N) ->
	tut4:getnum(N).<pre name="code" class="plain">
</span>

<span style="font-size:18px;">-module(tut4).
-export([getnum/1]).


getnum(Name) ->
	case Name of
		a -> 1;
		b -> 2
	end.
</span>

fun使用:

<span style="font-size:18px;">-module(tut).
-export([for/3]).


for(Max,Max,F) ->
	[F(Max)];

for(I,Max,F) ->
	[F(I) | for(I + 1,Max,F)].</span><pre name="code" class="plain"><span style="font-size:18px;">
</span>

<span style="font-size:18px;">41> c(tut).
{ok,tut}
42> tut:for(1,5,fun(I) -> 2*I end).
[2,4,6,8,10]
</span>

<span style="font-size:18px;">-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> </span>

<span style="font-size:18px;">-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> </span>

<span style="font-size:18px;">-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> </span>

列表解析：

<span style="font-size:18px;">-module(tut).
-export([map/2]).

map(F,L) ->
	[F(X) || X <- L].
</span>

快速排序：

<span style="font-size:18px;">-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> </span>

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>