blocks|key|120963|text|toInt可能会在解析时失败。您需要使用case语句来检查它：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|120964|case+toInt+str+of
++Err+msg+->+...+--+do+something+with+the+error+message
++Ok+val+->+...+--+val+is+an+Int+which+you+can+add|code-block|syntax|javascript|120965|More+about+Result+here|offset|length|120966|entityMap|0|LINK|mutability|MUTABLE|url|http://package.elm-lang.org/packages/elm-lang/core/1.0.0/Result^0|0|0|0|M|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@]|9|@$I|V|J|W|1|X]]|A|$]]|$1|K|3|-4|5|6|7|Y|8|@]|9|@]|A|$]]]|L|$M|$5|N|O|P|A|$Q|R]]]]

toInt can fail in parsing. You need to check it using a case statement:

<pre><code>case toInt str of
 Err msg -&gt; ... -- do something with the error message
 Ok val -&gt; ... -- val is an Int which you can add
</code></pre>

<a href="http://package.elm-lang.org/packages/elm-lang/core/1.0.0/Result">More about Result here</a>

blocks|key|2677153|text|下面是如何为转换提供默认值，以防解析失败。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2677154|String.toInt+"5"+%7C>+Result.toMaybe+%7C>+Maybe.withDefault+0|code-block|syntax|javascript|2677155|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Here's how to supply the conversion with a default value in case the parsing fails.

<pre><code>String.toInt "5" |&gt; Result.toMaybe |&gt; Maybe.withDefault 0
</code></pre>

blocks|key|2677157|text|也可以使用以下命令提取该整数|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2677158|Result.withDefault+0+(String.toInt+"2")|code-block|syntax|javascript|2677159|你可以阅读更多关于它的here|offset|length|2677160|entityMap|0|LINK|mutability|MUTABLE|url|http://package.elm-lang.org/packages/elm-lang/core/5.0.0/String#toInt^0|0|0|B|4|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@]|9|@$I|V|J|W|1|X]]|A|$]]|$1|K|3|-4|5|6|7|Y|8|@]|9|@]|A|$]]]|L|$M|$5|N|O|P|A|$Q|R]]]]

The integer can also be pulled out using

<pre><code>Result.withDefault 0 (String.toInt "2")
</code></pre>

You can read more about it <a href="http://package.elm-lang.org/packages/elm-lang/core/5.0.0/String#toInt" rel="noreferrer">here</a>

blocks|key|2888739|text|根据Elm+String+reference+documentation的说法，如果您从一些原始用户输入中提取一个数字，您通常会希望使用Result.withDefault来处理坏数据，以防解析失败。您可以使用管道链接此操作，以获得更清晰的代码：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2888740|String.toInt+"5"+%7C>+Result.withDefault+0|code-block|syntax|javascript|2888741|entityMap|0|LINK|mutability|MUTABLE|url|http://package.elm-lang.org/packages/elm-lang/core/5.0.0/String#toInt^0|1W|I|2|Y|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@$9|T|A|U|B|C]]|D|@$9|V|A|W|1|X]]|E|$]]|$1|F|3|G|5|H|7|Y|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|Z|8|@]|D|@]|E|$]]]|L|$M|$5|N|O|P|E|$Q|R]]]]

According to the <a href="http://package.elm-lang.org/packages/elm-lang/core/5.0.0/String#toInt" rel="nofollow noreferrer">Elm String reference documentation</a>, if you are extracting a number from some raw user input, you will typically want to use <code>Result.withDefault</code> to handle bad data in case parsing fails. You can chain this operation using pipes for cleaner code:

<pre><code>String.toInt "5" |&gt; Result.withDefault 0
</code></pre>

blocks|key|2677176|text|使用map：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2677177|answer+=+Result.map2+(%2B)+(String.toInt+"1")+(String.toInt+"2")|code-block|syntax|javascript|2677178|map2|offset|length|2677179|2677180|将函数应用于两个结果，如果两个结果都是Ok的。如果不是，则第一个参数是错误，将传播通过。|blockquote|2677181|2677182|2677183|将add结果作为字符串|style|CODE|2677184|resultAsString+r+=
++++case+r+of
++++++++Err+msg+->+msg
++++++++Ok+value+->+toString+value

resultAsString+answer|2677185|为了简化操作，您可以创建一个addStrings函数：|2677186|addStrings+:+String+->+String+->+Result+String+Int
addStrings+a+b+=
++++Result.map2+(%2B)+(String.toInt+a)+(String.toInt+b)|2677187|您甚至可以完全使用Result类型：|2677188|addStrings+:+String+->+String+->+String
addStrings+a+b+=
++++let
++++++++r+=
++++++++++++Result.map2+(%2B)+(String.toInt+a)+(String.toInt+b)
++++in
++++case+r+of
++++++++Err+msg+->
++++++++++++msg

++++++++Ok+value+->
++++++++++++toString+value|2677189|测试|2677190|import+Html+exposing+(Html,+text)

main+:+Html+msg
main+=
++++text+(addStrings+"1"+"2")


output+3|2677191|entityMap|0|LINK|mutability|MUTABLE|url|http://package.elm-lang.org/packages/elm-lang/core/5.0.0/Result#map2^0|0|0|0|4|0|0|0|0|0|0|1|3|0|0|E|A|0|0|9|6|0|0|0|0^^$0|@$1|2|3|4|5|6|7|1G|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|1H|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|1I|8|@]|9|@$I|1J|J|1K|1|1L]]|A|$]]|$1|K|3|-4|5|6|7|1M|8|@]|9|@]|A|$]]|$1|L|3|M|5|N|7|1N|8|@]|9|@]|A|$]]|$1|O|3|-4|5|6|7|1O|8|@]|9|@]|A|$]]|$1|P|3|-4|5|6|7|1P|8|@]|9|@]|A|$]]|$1|Q|3|R|5|6|7|1Q|8|@$I|1R|J|1S|S|T]]|9|@]|A|$]]|$1|U|3|V|5|D|7|1T|8|@]|9|@]|A|$E|F]]|$1|W|3|X|5|6|7|1U|8|@$I|1V|J|1W|S|T]]|9|@]|A|$]]|$1|Y|3|Z|5|D|7|1X|8|@]|9|@]|A|$E|F]]|$1|10|3|11|5|6|7|1Y|8|@$I|1Z|J|20|S|T]]|9|@]|A|$]]|$1|12|3|13|5|D|7|21|8|@]|9|@]|A|$E|F]]|$1|14|3|15|5|6|7|22|8|@]|9|@]|A|$]]|$1|16|3|17|5|D|7|23|8|@]|9|@]|A|$E|F]]|$1|18|3|-4|5|6|7|24|8|@]|9|@]|A|$]]]|19|$1A|$5|1B|1C|1D|A|$1E|1F]]]]

Use map:

<pre><code>answer = Result.map2 (+) (String.toInt "1") (String.toInt "2")
</code></pre>

<a href="http://package.elm-lang.org/packages/elm-lang/core/5.0.0/Result#map2" rel="nofollow noreferrer">map2</a>:

<blockquote>
 Apply a function to two results, if both results are Ok. If not, the
 first argument which is an Err will propagate through.
</blockquote>

to have the <code>add</code> result as a string

<pre><code>resultAsString r =
 case r of
 Err msg -&gt; msg
 Ok value -&gt; toString value

resultAsString answer
</code></pre>

to make things easier you can create an <code>addStrings</code> function:

<pre><code>addStrings : String -&gt; String -&gt; Result String Int
addStrings a b =
 Result.map2 (+) (String.toInt a) (String.toInt b)
</code></pre>

You can even get away with the <code>Result</code> type altogether:

<pre><code>addStrings : String -&gt; String -&gt; String
addStrings a b =
 let
 r =
 Result.map2 (+) (String.toInt a) (String.toInt b)
 in
 case r of
 Err msg -&gt;
 msg

 Ok value -&gt;
 toString value
</code></pre>

Testing

<pre><code>import Html exposing (Html, text)

main : Html msg
main =
 text (addStrings "1" "2")


output 3
</code></pre>

blocks|key|2677362|text|大多数情况下，您需要所有可能的值，而默认值并不合适。这里我提供了一个结果类型检查函数，您可以使用它来决定是否使用转换后的值：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2677363|isErrorResult+r+=
++++case+r+of
++++++++Err+msg+->
++++++++++++True

++++++++Ok+value+->
++++++++++++False|code-block|syntax|javascript|2677364|你可以这样使用它：|2677365|r+=+String.toInt+"20b"

if+isErrorResult+r+then
++++--+not+a+valid+Interger,+abort+or+whatever
else
++++--+a+good+integer,+extract+it
++++a+=+Result.withDefault+0+r
++++--+and+make+good+use+of+it|2677366|传递给withDefault的default值(在本例中为0)没有意义，因为我们确保r不是Err。|offset|length|style|CODE|2677367|entityMap^0|0|0|0|0|3|B|F|7|16|1|19|3|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|W|8|@$M|X|N|Y|O|P]|$M|Z|N|10|O|P]|$M|11|N|12|O|P]|$M|13|N|14|O|P]]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|15|8|@]|9|@]|A|$]]]|R|$]]

The <code>withDefault</code> method forces you to define a value that can be used for calculations but it is not always possible to establish a value that is significant for errors. Most often you need all the possible values, and default is not fit. Here I provide a result type check function you can use to decide if you use or not the converted value:

<pre><code>isErrorResult r =
 case r of
 Err msg -&gt;
 True

 Ok value -&gt;
 False
</code></pre>

You can use it like this:

<pre><code>r = String.toInt "20b"

if isErrorResult r then
 -- not a valid Interger, abort or whatever
else
 -- a good integer, extract it
 a = Result.withDefault 0 r
 -- and make good use of it
</code></pre>

the <code>default</code> value (0 in this case) passed to <code>withDefault</code> is meaningless, because we made sure that <code>r</code> is not an <code>Err</code>.

blocks|key|123927|text|您可以这样做，如下所示。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|123928|----+Elm+0.19.0+----------------------------------------------------------------
Read+<https://elm-lang.org/0.19.0/repl>+to+learn+more:+exit,+help,+imports,+etc.
--------------------------------------------------------------------------------
>+parseInt+string+=+String.toInt+string
<function>+:+String+->+Maybe+Int
>+resultParseInt+string+=+\
%7C+++Result.fromMaybe+("error+parsing+string:+"+%2B%2B+string)+(parseInt+string)
<function>+:+String+->+Result+String+Int
>+resultParseInt+"12"
Ok+12+:+Result+String+Int
>+resultParseInt+"12ll"
Err+("error+parsing+string:+12ll")+:+Result+String+Int
>|code-block|syntax|javascript|123929|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

You can do this as below.

<pre><code>---- Elm 0.19.0 ----------------------------------------------------------------
Read &lt;https://elm-lang.org/0.19.0/repl&gt; to learn more: exit, help, imports, etc.
--------------------------------------------------------------------------------
&gt; parseInt string = String.toInt string
&lt;function&gt; : String -&gt; Maybe Int
&gt; resultParseInt string = \
| Result.fromMaybe ("error parsing string: " ++ string) (parseInt string)
&lt;function&gt; : String -&gt; Result String Int
&gt; resultParseInt "12"
Ok 12 : Result String Int
&gt; resultParseInt "12ll"
Err ("error parsing string: 12ll") : Result String Int
&gt;
</code></pre>

blocks|key|121929|text|我改变了一些人的答案，因为它似乎是可能的类型|type|unstyled|depth|inlineStyleRanges|entityRanges|data|121930|isErrorResult+:+String+->+Bool
isErrorResult+r+=
case+String.toInt+r+of
++++Nothing+->+True
++++Just+value+->+False|code-block|syntax|javascript|121931|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

I have changed guys answers a bit, since it appears to be of type Maybe

<pre><code>isErrorResult : String -&gt; Bool
isErrorResult r =
case String.toInt r of
 Nothing -&gt; True
 Just value -&gt; False
</code></pre>

blocks|key|2677376|text|Maybe.withDefault+0+(String.toInt+"42")|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|2677377|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>Maybe.withDefault 0 (String.toInt "42")
</code></pre>

I am trying to convert a string to integer using String.toInt. However, when I want to bind the result to a variable and then do some simple math with it I get this error:

<blockquote>
 Function <code>add</code> is expecting the 2nd argument to be:

<pre><code>Int
</code></pre>
 
 But it is:

<pre><code>Result String Int
</code></pre>
</blockquote>

How can I just extract the integer part of the result?

String to int conversion using toInt function

我正在尝试使用String.toInt将字符串转换为整数。然而，当我想要将结果绑定到一个变量，然后对它进行一些简单的数学运算时，我得到了这个错误：函数add期望第二个参数为：整型但它确实是：结果字符串Int如何才能只提取结果的整数部分？

问使用toInt函数将字符串转换为整型
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