Erlang学习二

矫情吗；* 2022-08-13 15:52 17阅读 0赞

# [Erlang学习][Erlang]二 #

[http://www.erlang.org/download/getting\_started-5.4.pdf ][http_www.erlang.org_download_getting_started-5.4.pdf]

**错误提示：**

（1）

-module(tut).
 -export([fac/1]).
 
 
 fac(1) ->
 	1.
 
 fac(X) ->
 	X * fac(X - 1).<pre name="code" class="plain">

11> c(tut).
 tut.erl:8: function fac/1 already defined
 error
 12>

（2）

-module(tut).
 -export([fac/1]).
 
 
 fac(1) ->
 	1;
 
 fac(X) ->
 	X * fac(X - 1).
 
 
 
 13> c(tut).
 {ok,tut}
 14>

（3）

-module(tut).
 -export([fac/1]).
 
 
 
 
 fac(X) ->
 	X * fac(X - 1);
 
 
 
 fac(1) ->
 	1.
 
 
 U14> c(tut).
 tut.erl:12: Warning: this clause cannot match because a previous clause at line 7 always matches
 {ok,tut}
 15>

只有（2）运行阶乘才正确，若执行（3）将死循环，因为从上向下匹配函数。

### tuple: ###

-module(tut).
 -export([convert/1]).
 
 
 
 convert({inch,X}) ->
 	{inch,X/2.54}.
 
 
 20> tut:convert({inch,2}).
 {inch,0.7874015748031495}
 21> tut:convert(1). 
 ** exception error: no function clause matching tut:convert(1) (tut.erl, line 6)
 22>

**list:**

-module(tut).
    -export([listlen/1]).
    
    listlen([]) ->
    	0;
    
    
    listlen([Head | Rest]) ->
    	1 + listlen(Rest).

###  ###

### io:format ###

42> io:format(""). 
 ok
 43> io:format("1~n").
 1
 ok
 44> io:format("1~n~w",[1]).
 1
 1ok
 45> io:format("1~n~w",[1,atom]).
 ** exception error: bad argument
 in function io:format/3
 called as io:format(<0.25.0>,"1~n~w",[1,atom])
 46>

~w按顺序替换第二个列表的每项，~n替换新行

**test:**

-module(tut).
    -export([format/1]).
    
    %hello world
    
    
    format([]) ->
    	ok;
    
    
    format([City | Rest]) ->
    	print(convert(City)),
    	format(Rest).
    
    
    convert({Name,{c,Temp}}) ->
    	{Name,{c,Temp}};
    
    
    convert({Name,{f,Temp}}) ->
    	{Name,{c,(Temp - 32) * 5 / 9}}.
    
    
    print({Name,{c,Temp}}) ->
    	io:format("~-15w ~w c~n",[Name,Temp]).
    
    
    
    54> tut:format([]).
    ok
    55> tut:format([2,3]).
    ** exception error: no function clause matching tut:convert(2) (tut.erl, line 16)
         in function  tut:format/1 (tut.erl, line 12)
    56> tut:format([{Bj,{f,12}},{jp,{c,12}}]).
    * 1: variable 'Bj' is unbound
    57> tut:format([{bj,{f,12}},{jp,{c,12}}]).
    bj              -11.11111111111111 c
    jp              12 c
    ok
    58>

**求最大值：**

-module(tut).
    -export([getmax/1]).
    
    
    getmax([]) ->
    	ok;
    
    
    getmax([Head | Rest]) ->
    	getmax(Rest,Head).
    
    
    
    getmax([],Max) ->
    	Max;
    
    
    getmax([Head | Rest],Max) when Head > Max ->
    	Tem = Head,
    	getmax(Rest,Tem);
    
    
    getmax([Head | Rest],Max) ->
    	getmax(Rest,Max).
    
    
    
    
    67> c(tut).
    tut.erl:23: Warning: variable 'Head' is unused
    {ok,tut}
    68> tut:getmax([2,3,4,1,5]).
    5
    69>

[Erlang]: http://blog.csdn.net/nawenqiang/article/details/40742215
[http_www.erlang.org_download_getting_started-5.4.pdf]: http://www.erlang.org/download/getting_started-5.4.pdf