erlang领悟

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 hello\n").
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：