blocks|key|1327428|text|您始终可以定义单独的运算符，或使用阴影，或使用括号来创建临时阴影的内部作用域：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1327429|let+f()+=
++++//+define+a+separate+operator
++++let+(%2B.)+x+y+=+Checked.(%2B)+x+y
++++try+
++++++++let+x+=+1+%2B.+System.Int32.MaxValue
++++++++printfn+"ran+ok"
++++with+e+->
++++++++printfn+"exception"
++++try+
++++++++let+x+=+1+%2B+System.Int32.MaxValue
++++++++printfn+"ran+ok"
++++with+e+->
++++++++printfn+"exception"
++++//+shadow+(%2B)
++++let+(%2B)+x+y+=+Checked.(%2B)+x+y
++++try+
++++++++let+x+=+1+%2B+System.Int32.MaxValue
++++++++printfn+"ran+ok"
++++with+e+->
++++++++printfn+"exception"
++++//+shadow+it+back+again
++++let+(%2B)+x+y+=+Operators.(%2B)+x+y
++++try+
++++++++let+x+=+1+%2B+System.Int32.MaxValue
++++++++printfn+"ran+ok"
++++with+e+->
++++++++printfn+"exception"
++++//+use+parens+to+create+a+scope
++++(
++++++++//+shadow+inside
++++++++let+(%2B)+x+y+=+Checked.(%2B)+x+y
++++++++try+
++++++++++++let+x+=+1+%2B+System.Int32.MaxValue
++++++++++++printfn+"ran+ok"
++++++++with+e+->
++++++++++++printfn+"exception"
++++)++++++++++++
++++//+shadowing+scope+expires
++++try+
++++++++let+x+=+1+%2B+System.Int32.MaxValue
++++++++printfn+"ran+ok"
++++with+e+->
++++++++printfn+"exception"


f()++++
//+output:
//+exception
//+ran+ok
//+exception
//+ran+ok
//+exception
//+ran+ok|code-block|syntax|javascript|1327430|最后，另请参阅--checked%2B编译器选项：|offset|length|style|CODE|1327431|http://msdn.microsoft.com/en-us/library/dd233171(VS.100).aspx|1327432|entityMap|0|LINK|mutability|MUTABLE|url^0|0|0|7|A|0|0|1P|0|0^^$0|@$1|2|3|4|5|6|7|V|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|W|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|X|8|@$I|Y|J|Z|K|L]]|9|@]|A|$]]|$1|M|3|N|5|6|7|10|8|@]|9|@$I|11|J|12|1|13]]|A|$]]|$1|O|3|-4|5|6|7|14|8|@]|9|@]|A|$]]]|P|$Q|$5|R|S|T|A|$U|N]]]]

You can always define a separate operator, or use shadowing, or use parens to create an inner scope for temporary shadowing:

<pre><code>let f() =
 // define a separate operator
 let (+.) x y = Checked.(+) x y
 try 
 let x = 1 +. System.Int32.MaxValue
 printfn "ran ok"
 with e -&gt;
 printfn "exception"
 try 
 let x = 1 + System.Int32.MaxValue
 printfn "ran ok"
 with e -&gt;
 printfn "exception"
 // shadow (+)
 let (+) x y = Checked.(+) x y
 try 
 let x = 1 + System.Int32.MaxValue
 printfn "ran ok"
 with e -&gt;
 printfn "exception"
 // shadow it back again
 let (+) x y = Operators.(+) x y
 try 
 let x = 1 + System.Int32.MaxValue
 printfn "ran ok"
 with e -&gt;
 printfn "exception"
 // use parens to create a scope
 (
 // shadow inside
 let (+) x y = Checked.(+) x y
 try 
 let x = 1 + System.Int32.MaxValue
 printfn "ran ok"
 with e -&gt;
 printfn "exception"
 ) 
 // shadowing scope expires
 try 
 let x = 1 + System.Int32.MaxValue
 printfn "ran ok"
 with e -&gt;
 printfn "exception"


f() 
// output:
// exception
// ran ok
// exception
// ran ok
// exception
// ran ok
</code></pre>

Finally, see also the <code>--checked+</code> compiler option:

<a href="http://msdn.microsoft.com/en-us/library/dd233171(VS.100).aspx" rel="noreferrer">http://msdn.microsoft.com/en-us/library/dd233171(VS.100).aspx</a>

blocks|key|1327509|text|这里有一个复杂(但可能很有趣)的替代方案。如果你正在写一些严肃的东西，那么你可能应该使用Brians的建议之一，但出于好奇，我想知道是否有可能编写F#计算表达式来实现这一点。您可以声明一个表示int的类型，该类型只能与选中的操作一起使用：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1327510|type+CheckedInt+=+Ch+of+int+with
++static+member+(%2B)+(Ch+a,+Ch+b)+=+Checked.(%2B)+a+b
++static+member+(*)+(Ch+a,+Ch+b)+=+Checked.(*)+a+b
++static+member+(%2B)+(Ch+a,+b)+=+Checked.(%2B)+a+b
++static+member+(*)+(Ch+a,+b)+=+Checked.(*)+a+b|code-block|syntax|javascript|1327511|然后，您可以定义一个计算表达式构建器(这根本不是真正的monad，因为操作类型完全是非标准的)：|1327512|type+CheckedBuilder()+=+
++member+x.Bind(v,+f)+=+f+(Ch+v)++++++
++member+x.Return(Ch+v)+=+v
let+checked+=+new+CheckedBuilder()++|1327513|当你调用‘checked’时，它会自动将给定的整数值包装成一个整数，该整数应该与绑定操作一起使用，因此其余的代码将使用声明为成员的选中的%2B和*运算符。你最终会得到类似这样的结果：|1327514|checked+{+let!+a+=+10000+
++++++++++let!+b+=+a+*+10000+
++++++++++let!+c+=+b+*+21+
++++++++++let!+d+=+c+%2B+47483648+//+!
++++++++++return+d+}|1327515|这会抛出异常，因为它会在标记的行上溢出。如果更改数字，它将返回一个int值(因为Return成员从Checked类型中展开数值)。这是一个有点疯狂的技巧:-)但我想这可能会很有趣！|1327516|(注意，checked是一个保留供将来使用的关键字，因此您可能更喜欢选择其他名称)|1327517|entityMap^0|2O|3|0|0|0|0|5|7|1W|1|1Y|1|0|0|X|3|14|6|1D|7|0|4|7|0^^$0|@$1|2|3|4|5|6|7|Y|8|@$9|Z|A|10|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|11|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|12|8|@]|D|@]|E|$]]|$1|M|3|N|5|H|7|13|8|@]|D|@]|E|$I|J]]|$1|O|3|P|5|6|7|14|8|@$9|15|A|16|B|C]|$9|17|A|18|B|C]|$9|19|A|1A|B|C]]|D|@]|E|$]]|$1|Q|3|R|5|H|7|1B|8|@]|D|@]|E|$I|J]]|$1|S|3|T|5|6|7|1C|8|@$9|1D|A|1E|B|C]|$9|1F|A|1G|B|C]|$9|1H|A|1I|B|C]]|D|@]|E|$]]|$1|U|3|V|5|6|7|1J|8|@$9|1K|A|1L|B|C]]|D|@]|E|$]]|$1|W|3|-4|5|6|7|1M|8|@]|D|@]|E|$]]]|X|$]]

Here is a complicated (but maybe interesting) alternative. If you're writing something serious then you should probably use one of the Brians suggestions, but just out of curiosity, I was wondering if it was possible to write F# computation expression to do this. You can declare a type that represents <code>int</code> which should be used only with checked operations:

<pre><code>type CheckedInt = Ch of int with
 static member (+) (Ch a, Ch b) = Checked.(+) a b
 static member (*) (Ch a, Ch b) = Checked.(*) a b
 static member (+) (Ch a, b) = Checked.(+) a b
 static member (*) (Ch a, b) = Checked.(*) a b
</code></pre>

Then you can define a computation expression builder (this isn't really a monad at all, because the types of operations are completely non-standard):

<pre><code>type CheckedBuilder() = 
 member x.Bind(v, f) = f (Ch v) 
 member x.Return(Ch v) = v
let checked = new CheckedBuilder() 
</code></pre>

When you call 'bind' it will automatically wrap the given integer value into an integer that should be used with <code>checked</code> operations, so the rest of the code will use checked <code>+</code> and <code>*</code> operators declared as members. You end up with something like this:

<pre><code>checked { let! a = 10000 
 let! b = a * 10000 
 let! c = b * 21 
 let! d = c + 47483648 // !
 return d }
</code></pre>

This throws an exception because it overflows on the marked line. If you change the number, it will return an <code>int</code> value (because the <code>Return</code> member unwraps the numeric value from the <code>Checked</code> type). This is a bit crazy technique :-) but I thought it may be interesting!

(Note <code>checked</code> is a keyword reserved for future use, so you may prefer choosing another name)

F# allows to use checked arithmetics by opening <code>Checked</code> module, which redefines standard operators to be checked operators, for example:

<pre><code>open Checked
let x = 1 + System.Int32.MaxValue // overflow
</code></pre>

will result arithmetic overflow exception.

But what if I want to use checked arithmetics in some small scope, like C# allows with keyword <code>checked</code>:

<pre><code>int x = 1 + int.MaxValue; // ok
int y = checked { 1 + int.MaxValue }; // overflow
</code></pre>

How can I control the scope of operators redefinition by opening <code>Checked</code> module or make it smaller as possible?

F# Checked Arithmetics Scope

编译器

通过打开Checked模块，F#允许使用已检查的算术，该模块重新定义了要检查的标准运算符，例如：open Checkedlet x = 1 + System.Int32.MaxValue // overflow将导致算术溢出异常。但是，如果我想在小范围内使用校验算法，比如C#允许使用关键字checked怎么办int x...

问F#检查算术作用域
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