Erlang 代码将不带分隔符的字符串拆分并放入列表

Question

我对 Erlang 编程非常陌生。我正在制作一个解码盲文的程序，但我在尝试在没有分隔符的情况下每 2 个字符拆分一个字符串并将它们放入列表时遇到问题。

首先我读的是这样的盲文字母:

inKey(Key1) -> Key1.
inKey2(Key2) -> Key2.
inKey3(Key3) -> Key3.

键 1-3 是字符串，如下所示:"x.x.xxxxx.xxxxx..x.xx.x.xxxxx.xxxxx..x.xx.x..xxxxxx." 这些3 个键构成盲文信息，我稍后将使用这些信息将盲文转换为普通字符。

现在我需要拆分这个字符串并将它们放在一个列表中，使其看起来像这样:["x.","x.","xx","xx",x.", "xx","xx","x.",".x 等等。

如果字符串被拆分，我想将它们插入到我的编码列表中，如字符 A 的连音中所示

 Code=[#row{name="R1",alfabet=[#codes{letter="A",braille="X."},#codes{letter="B",braille=""}

有人可以帮帮我吗？

`

Answer 1

在 Erlang 中，你需要记住一个字符串相当于一个数字列表，其中的数字是每个字符的 ascii 代码。令人困惑的是，有时 shell 将数字列表显示为字符串，有时将数字列表显示为数字列表。这是 erlang shell 的一个可怕特性。

不管 shell 显示什么，只要记住字符串是一个数字列表。那么问题就变成了，如果你想输出一个数字列表而不是一个字符串怎么办？答案是:你对此无能为力；外壳可能会将您的数字列表显示为字符串...除非您采取进一步措施:

45> Grades = [97,98,99].
"abc"

Wtf??!

46> io:format("~w~n", [Grades]).
[97,98,99]
ok

另一种思考方式是:erlang 字符串语法 "abc" 只是创建数字列表的快捷方式 [97,98,99] .

接下来，您可以使用如下模式解构列表:

[Head|Tail] = [1,2,3]

在外壳中:

8> [Head|Tail] = [1, 2, 3, 4].
[1,2,3,4]

9> Head.                      
1

10> Tail.
[2,3,4]

但是，cons 运算符 | 比这更灵活，它允许你这样做:

13> [N1,N2 | T] = [1, 2, 3, 4].   
[1,2,3,4]

14> N1.
1

15> N2.
2

16> T.
[3,4]

因此，您可以这样做:

-module(my).
-compile(export_all).

string() ->
    "x.x.xxxxx.xxxxx..x.xx.x.xxxxx.xxxxx..x.xx.x..xxxxxx.".

chunk2([]) -> [];
chunk2([N1, N2| Tail]) ->
    [[N1,N2] | chunk2(Tail) ].

在外壳中:

2> c(my).
my.erl:2: Warning: export_all flag enabled - all functions will be exported
{ok,my}

3> my:chunk2(my:string()).  
["x.","x.","xx","xx","x.","xx","xx","x.",".x",".x","x.",
 "x.","xx","xx","x.","xx","xx","x.",".x",".x","x.","x.",".x",
 "xx","xx","x."]

4> 

最后，要构造一个#code{}记录列表，你可以这样做:

-module(my).
-compile(export_all).
-record(codes, {letter, braille}).

string() ->
    "x.x.xxxxx.xxxxx..x.xx.x.xxxxx.xxxxx..x.xx.x..xxxxxx.".

chunk2([]) -> [];
chunk2([N1, N2| Tail]) ->
    [[N1,N2] | chunk2(Tail) ].

make_record_list(Letters, Chunks) ->
    lists:zipwith(
        fun(Letter, Chunk) -> #codes{letter=[Letter], braille=Chunk} end,
        Letters,
        Chunks
    ).

在外壳中:

31> c(my).             
my.erl:2: Warning: export_all flag enabled - all functions will be exported
{ok,my}

32> ListOfCapLetters = lists:seq($A, $Z).
"ABCDEFGHIJKLMNOPQRSTUVWXYZ"

33> BrailleChunks = my:chunk2(my:string()).
["x.","x.","xx","xx","x.","xx","xx","x.",".x",".x","x.",
 "x.","xx","xx","x.","xx","xx","x.",".x",".x","x.","x.",".x",
 "xx","xx","x."]

34> Records = my:make_record_list(ListOfCapLetters, BrailleChunks).
[{codes,"A","x."},
 {codes,"B","x."},
 {codes,"C","xx"},
 {codes,"D","xx"},
 {codes,"E","x."},
 {codes,"F","xx"},
 {codes,"G","xx"},
 {codes,"H","x."},
 {codes,"I",".x"},
 {codes,"J",".x"},
 {codes,"K","x."},
 {codes,"L","x."},
 {codes,"M","xx"},
 {codes,"N","xx"},
 {codes,"O","x."},
 {codes,"P","xx"},
 {codes,"Q","xx"},
 {codes,"R","x."},
 {codes,"S",".x"},
 {codes,"T",".x"},
 {codes,"U","x."},
 {codes,"V","x."},
 {codes,"W",".x"},
 {codes,"X","xx"},
 {codes,"Y","xx"},
 {codes,"Z",[...]}]

看来最后一条记录可能有问题，我们检查一下:

37> tl(Records).  
[{codes,"B","x."},
 {codes,"C","xx"},
 {codes,"D","xx"},
 {codes,"E","x."},
 {codes,"F","xx"},
 {codes,"G","xx"},
 {codes,"H","x."},
 {codes,"I",".x"},
 {codes,"J",".x"},
 {codes,"K","x."},
 {codes,"L","x."},
 {codes,"M","xx"},
 {codes,"N","xx"},
 {codes,"O","x."},
 {codes,"P","xx"},
 {codes,"Q","xx"},
 {codes,"R","x."},
 {codes,"S",".x"},
 {codes,"T",".x"},
 {codes,"U","x."},
 {codes,"V","x."},
 {codes,"W",".x"},
 {codes,"X","xx"},
 {codes,"Y","xx"},
 {codes,"Z","x."}]

不，第一个输出刚刚达到 shell 愿意显示的限制。

注意，ListOfCapLetters 的每个元素都是一个数字，而一个数字又不是一个列表，所以 ListOfCapLetters 的每个元素本身都不是一个字符串。要从数字创建字符串，您需要将其放入列表中，因此是 [Letter]。 String = [97,98,99] 和 ListOfStrings = [[97], [98], [99]] 之间的区别相同:

40> String = [97,98,99].
"abc"

41> hd(String).
97

42> ListOfStrings = [[97], [98], [99]].
["a","b","c"]

43> hd(ListOfStrings).
"a"

lists:seq() 返回 String 的等价物。

对评论的回应:

见 lists:keyfind/3 :

20> TargetRecord = lists:keyfind("xx", 3, Records).                
#codes{letter = "C",braille = "xx"}

21> rr(my).  %Read record definition contained in my.erl into the shell.                                                     
[codes]

22> TargetRecord#codes.letter.
"C"

字符串 "C" 实际上是列表 [67]，shell 决定将其显示为 "C"。你需要能够查找一个 ascii 表来发现一个字符串在 Erlang 中真正代表什么。或者，您可以像这样获取字符的 ascii 代码:

24> $C.
67

25> $a.
97

所以，"C"其实就是列表[67]，"a"其实就是列表[97]。