erlang领悟 - 瀚海星空

2013-08-06

abloz.com

周海汉 /文 2013.8.6

erlang作为著名的并发编程语言，在大规模并发计算上很独到。但它的怪异的语法和独特的约定，让学习曲线很陡。OTP意思是open telecom platform.

1.编译安装：

很中规中矩，一点不特殊。

wget http://www.erlang.org/download/otp_src_R16B01.tar.gz

./configure

make

sudo make install

erl shell

strider 1> erl
Erlang (BEAM) emulator version 5.3 [hipe] [threads:0]

Eshell V5.3  (abort with ^G)
1>Str = "abcd".
"abcd"
2> L = length(Str).
4
3> Descriptor = {L, list_to_atom(Str)}.
{4,abcd}
4> L.
4
5> b().
Descriptor = {4,abcd}
L = 4
Str = "abcd"
ok
6> f(L).
ok
7> b().
Descriptor = {4,abcd}
Str = "abcd"
ok
8> f(L).
ok
9> {L, _} = Descriptor.
{4,abcd}
10> L.
4
11> {P, Q, R} = Descriptor.
** exception error: no match of right hand side value {4,abcd}
12> P.
* 1: variable 'P' is unbound **
13> Descriptor.
{4,abcd}
14>{P, Q} = Descriptor.
{4,abcd}
15> P.
4
16> f().
ok
17> put(aa, hello).
undefined
18> get(aa).
hello
19> Y = test1:demo(1).
11
20> get().
[{aa,worked}]
21> put(aa, hello).
worked
22> Z = test1:demo(2).
** exception error: no match of right hand side value 1
     in function  test1:demo/1
23> Z.
* 1: variable 'Z' is unbound **
24> get(aa).
hello
25> erase(), put(aa, hello).
undefined
26> spawn(test1, demo, [1]).
<0.57.0>
27> get(aa).
hello
28> io:format("hello hellon").
hello hello
ok
29> e(28).
hello hello
ok
30> v(28).
ok
31> c(ex).
{ok,ex}
32> rr(ex).
[rec]
33> rl(rec).
-record(rec,{a,b = val()}).
ok
34> #rec{}.
** exception error: undefined shell command val/0
35> #rec{b = 3}.
#rec{a = undefined,b = 3}
36> rp(v(-1)).
#rec{a = undefined,b = 3}
ok
37> rd(rec, {f = orddict:new()}).
rec
38> #rec{}.
#rec{f = []}
ok
39> rd(rec, {c}), A.
* 1: variable 'A' is unbound **
40> #rec{}.
#rec{c = undefined}
ok
41> test1:loop(0).
Hello Number: 0
Hello Number: 1
Hello Number: 2
Hello Number: 3

User switch command
 --> i
 --> c
.
.
.
Hello Number: 3374
Hello Number: 3375
Hello Number: 3376
Hello Number: 3377
Hello Number: 3378
** exception exit: killed
42> E = ets:new(t, []).
17
43> ets:insert({d,1,2}).
** exception error: undefined function ets:insert/1
44> ets:insert(E, {d,1,2}).
** exception error: argument is of wrong type
     in function  ets:insert/2
        called as ets:insert(16,{d,1,2})
45> f(E).
ok
46> catch_exception(true).
false
47> E = ets:new(t, []).
18
48> ets:insert({d,1,2}).
* exception error: undefined function ets:insert/1
49> ets:insert(E, {d,1,2}).
true
50> halt().
strider 2>

感受：
erlang 结束语句是句号"."。所以初次使用shell像python那样用不会有任何提示，也不报错。因为没有输入点好结束。
其变量是大写开头，并且绑定后不能改变内容。
pid!msg 表示往pid进程发送msg。-> 可以认为是函数定义，类似于C语言的大括号。

命令行用到的两个程序：

[hadoop@hs11 erl]$ cat test1.erl -module(test1). -export([demo/1, loop/1]).

demo(X) -> put(aa,hello), X + 10.

loop(N) -> io:format(“Hello Number: ~w~n”,[N]), loop(N+1).

[hadoop@hs11 erl]$ cat math1.erl -module(math1). -export([fib/1, fac/1]).

fib(0)->1; fib(1)->1; fib(N)->fib(N-1)+fib(N-2).

fac(0)->1; fac(N)->N*fac(N-1).

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