Question

有人可以从Erlang解释这种意外的列表理解陌生感吗？

4> [A+B || [A, B] <- [1, 2, 3, [5, 6]]].
"\v"

预期：11

得到："\v"

要获得预期的输出必须做些什么？

Answer 1

根据Erlang documentation：

字符串是代码点，具有UTF-8编码的代码点（UTF-8二进制文件）的二进制文件的列表，或两者的混合。

"abcd"               % is a valid string  
<<"abcd">>           % is a valid string  
["abcd"]             % is a valid string  
<<"abc..åäö"/utf8>>  % is a valid string  
<<"abc..åäö">>       % is NOT a valid string,  
                     % but a binary with Latin-1-encoded codepoints  
[<<"abc">>, "..åäö"] % is a valid string  
[atom]               % is NOT a valid string

所以在上面你在列表中得到整数11或[11]：

Eshell V8.3  (abort with ^G)
1> [A+B || [A, B] <- [1, 2, 3, [5, 6]]].
"\v"
%% With hd/1 function you can get first element (head) of a list
2> hd([A+B || [A, B] <- [1, 2, 3, [5, 6]]]).
11
3> [11].
"\v"

Erlang VM以字符串形式打印可打印列表。目前它支持两种可打印范围。 latin1，默认为unicode。

$ erl
Erlang/OTP 19 [erts-8.3] [source] [64-bit] [smp:8:8] [async-threads:10] [hipe] [kernel-poll:false]
Eshell V8.3  (abort with ^G)
1> io:printable_range().
latin1

您可以使用+pc标记将latin1更改为unicode：

$ erl
Erlang/OTP 19 [erts-8.3] [source] [64-bit] [smp:8:8] [async-threads:10] [hipe] [kernel-poll:false]
Eshell V8.3  (abort with ^G)
1> [1662]. %% not printable in latin1 range
[1662]
2> 
BREAK: (a)bort (c)ontinue (p)roc info (i)nfo (l)oaded
       (v)ersion (k)ill (D)b-tables (d)istribution
a
$ erl +pc unicode
Erlang/OTP 19 [erts-8.3] [source] [64-bit] [smp:8:8] [async-threads:10] [hipe] [kernel-poll:false]

Eshell V8.3  (abort with ^G)
1> [1662].
"پ"
2>

来自Erlang列表理解的意外值

1 个答案: