erlang - 列出 :foreach returns ok in Erlang

Question

我刚开始接触Erlang，觉得很难理解。我想将列表拆分为字符串，对其运行 string:titlecase，然后将其连接到字符串中。

namecase(Text) ->
    TextArray = string:split(Text, " ", all),
    lists:join(" ", lists:foreach(fun(Element) -> string:titlecase(Element) end, TextArray)).

但它失败并显示错误消息escript:异常错误:没有与lists匹配的函数子句:join(“”，ok)(lists.erl，第1449行)因为它返回ok ，为什么返回正常？

Answer 1

lists:foreach 不返回传递给它的函数返回的值。它旨在与只会引起副作用的功能(例如打印)一起使用。您正在寻找lists:map。

1> Text = "foo bar baz".
"foo bar baz"
2> TextArray = string:split(Text, " ", all).
["foo","bar","baz"]
3> lists:join(" ", lists:map(fun(Element) -> string:titlecase(Element) end, TextArray)).
["Foo"," ","Bar"," ","Baz"]

此外，可以使用 fun module:name/arity 语法使匿名函数更短:

4> lists:join(" ", lists:map(fun string:titlecase/1, TextArray)).
["Foo"," ","Bar"," ","Baz"]