我刚刚和 Chicago Boss 一起学习 Erlang,想知道我怎么能做类似的事情(在伪代码中):
foreach (items as item)
if (i % 10 == 0)
<tr>
endif
<td>...</td>
if (i++ % 10 == 0)
</tr>
endif
endforeach
在我的模板中?
我刚刚和 Chicago Boss 一起学习 Erlang,想知道我怎么能做类似的事情(在伪代码中):
foreach (items as item)
if (i % 10 == 0)
<tr>
endif
<td>...</td>
if (i++ % 10 == 0)
</tr>
endif
endforeach
在我的模板中?
Erlang 是函数式语言,所以惯用的方式是以函数式的方式来做。我们准备了功能,它将首先将您的数据制成表格:
-module(tabify).
-export([tabify/2]).
tabify(N, L) when is_list(L), is_integer(N), N > 0 ->
tabify_(N, L).
tabify_(_, []) -> [];
tabify_(N, L) ->
{Row, Rest} = row(L, N),
[Row|tabify_(N, Rest)].
row(L, N) ->
row(L, N, []).
row([], _, Accu) -> {lists:reverse(Accu), []};
row(Rest, 0, Accu) -> {lists:reverse(Accu), Rest};
row([H|T], N, Accu) -> row(T, N-1, [H|Accu]).
现在我们可以通过以下方式使用它:
1> c(tabify).
{ok,tabify}
2> Data = [integer_to_list(X) || X <- lists:seq(1,100)].
["1","2","3","4","5","6","7","8","9","10","11","12","13",
"14","15","16","17","18","19","20","21","22","23","24","25",
"26","27","28",
[...]|...]
3> Table = tabify:tabify(10,Data).
[["1","2","3","4","5","6","7","8","9","10"],
["11","12","13","14","15","16","17","18","19","20"],
["21","22","23","24","25","26","27","28","29","30"],
["31","32","33","34","35","36","37","38","39","40"],
["41","42","43","44","45","46","47","48","49","50"],
["51","52","53","54","55","56","57","58","59","60"],
["61","62","63","64","65","66","67","68","69","70"],
["71","72","73","74","75","76","77","78","79","80"],
["81","82","83","84","85","86","87","88","89","90"],
["91","92","93","94","95","96","97","98","99","100"]]
4> T = [["<tr>", [["<td>", Item, "</td>"] || Item <- Row ], "</tr>"]|| Row <- Table].
[["<tr>",
[["<td>","1","</td>"],
["<td>","2","</td>"],
...
而不是让 io 子系统完成其余的工作。上面的结构是众所周知的 iolist ,如果你把它放在任何 io 中,它将以与以下相同的方式正确序列化:
6> iolist_to_binary(T).
<<"<tr><td>1</td><td>2</td><td>3</td><td>4</td><td>5</td><td>6</td><td>7</td><td>8</td><td>9</td><td>10</td></tr><tr><t"...>>
如果表中有数千个项目并且效率至关重要,那么您可以将所有列表常量转换为二进制。也可以在Data
. 作为最后的手段,您可以tabify/2
以更有效但可读性更低的方式重写和格式化。
如果你需要“tabify”一个列表,你可以使用我刚刚创建的这个函数:
tab_list(List1) ->
lists:append(
lists:flatten(
lists:map(
fun({Item, Idx}) ->
if
((Idx - 1) rem 10) == 0 -> lists:concat(["<TR><TD>", Item, "</TD>"]);
(Idx rem 10) == 0 -> lists:concat(["<TD>", Item, "</TD></TR>"]);
true -> lists:concat(["<TD>", Item, "</TD>"])
end
end,
lists:zip(List1, lists:seq(1, length(List1)))
)
),
if (length(List1) rem 10) == 0 -> ""; true -> "</TR>" end
).
当传递一个类似的列表["a", "b", "c", "d", "e", "f", "g", "h", "i", "l", "m", "n", "o", "p", "q", "r", "s", "t", "u", "v", "z"]
时,会产生以下结果:
"<TR><TD>a</TD><TD>b</TD><TD>c</TD><TD>d</TD><TD>e</TD><TD>f</TD><TD>g</TD><TD>h</TD><TD>i</TD><TD>l</TD></TR><TR><TD>m</TD><TD>n</TD><TD>o</TD><TD>p</TD><TD>q</TD><TD>r</TD><TD>s</TD><TD>t</TD><TD>u</TD><TD>v</TD></TR><TR><TD>z</TD></TR>"
这是你需要的吗?只要问你有什么问题!