blocks|key|3881117|text|您可以随时通过命令:r重新加载您正在使用的模块。这将丢弃您所做的任何交互式绑定，如果您只是随便看看，这可能并不总是实用的。如果你没有实际使用一个模块，这也是可行的。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|3881118|entityMap^0|9|2|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|K|8|@]|D|@]|E|$]]]|G|$]]

You can always reload the module you're working in via the command <code>:r</code>. This will throw away any interactive bindings you have made, and that might not always be practical if you're just poking around. This also works if you're not actually using a module.

blocks|key|2563219|text|正如注释所指出的，您正在使用let将一个名称绑定到一个值，该值是应用函数的结果。如果你想保持值不变，不要在let中命名它！(或者只是不引用你已经在let中计算的值)。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2563220|entityMap^0|E|3|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|K|8|@]|D|@]|E|$]]]|G|$]]

As the comments note, you're using <code>let</code> to bind a name to a value which is the result of applying a function. If you want to keep the value around, don't name it in a let! (or just don't refer to the value you've already computed in a let).

blocks|key|101428|text|GHCi有一个%2Br选项，according+to+the+manual应该可以执行您想要的操作：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|101429|101430|通常，在加载的模块中对顶级表达式(也称为CAF或常量应用形式)的任何求值都会在求值之间保留。启用%2Br会导致在每次求值后丢弃顶级表达式的所有求值(它们在单个求值过程中仍会保留)。|blockquote|101431|101432|如果计算的顶级表达式占用大量空间，或者您需要可重复的性能测量，则此选项可能会有所帮助。|101433|101434|请注意，它讨论的是constant+applicative+forms，而不是函数。但是，我无法让它在您的示例中工作：|101435|Prelude>+:set+%2Br
Prelude>+:set+%2Bs
Prelude>+let+f+=+1+:+map+(2*)+f
(0.01+secs,+1222216+bytes)
Prelude>+last+$+show+$+f+!!+100000
'6'
(3.54+secs,+641914476+bytes)
Prelude>+last+$+show+$+f+!!+100000
'6'
(0.04+secs,+1634552+bytes)
Prelude>+last+$+show+$+f+!!+100000
'6'
(0.04+secs,+1603568+bytes)|code-block|syntax|javascript|101436|很明显，%2Br+only+works+for+compiled+code，尽管医生没有提到这一点。|101437|entityMap|0|LINK|mutability|MUTABLE|url|http://www.haskell.org/ghc/docs/latest/html/users_guide/ghci-set.html#id489786|1|http://www.haskell.org/haskellwiki/Constant_applicative_form|2|https://ghc.haskell.org/trac/ghc/ticket/1400^0|7|2|C|N|0|0|0|1C|2|0|0|0|0|9|Q|1|0|0|4|2|4|V|2|0^^$0|@$1|2|3|4|5|6|7|18|8|@$9|19|A|1A|B|C]]|D|@$9|1B|A|1C|1|1D]]|E|$]]|$1|F|3|-4|5|6|7|1E|8|@]|D|@]|E|$]]|$1|G|3|H|5|I|7|1F|8|@$9|1G|A|1H|B|C]]|D|@]|E|$]]|$1|J|3|-4|5|6|7|1I|8|@]|D|@]|E|$]]|$1|K|3|L|5|6|7|1J|8|@]|D|@]|E|$]]|$1|M|3|-4|5|6|7|1K|8|@]|D|@]|E|$]]|$1|N|3|O|5|6|7|1L|8|@]|D|@$9|1M|A|1N|1|1O]]|E|$]]|$1|P|3|Q|5|R|7|1P|8|@]|D|@]|E|$S|T]]|$1|U|3|V|5|6|7|1Q|8|@$9|1R|A|1S|B|C]]|D|@$9|1T|A|1U|1|1V]]|E|$]]|$1|W|3|-4|5|6|7|1W|8|@]|D|@]|E|$]]]|X|$Y|$5|Z|10|11|E|$12|13]]|14|$5|Z|10|11|E|$12|15]]|16|$5|Z|10|11|E|$12|17]]]]

GHCi has a <code>+r</code> option, which, <a href="http://www.haskell.org/ghc/docs/latest/html/users_guide/ghci-set.html#id489786" rel="nofollow noreferrer">according to the manual</a>, should do what you want:

<blockquote>
 Normally, any evaluation of top-level expressions (otherwise known as
 CAFs or Constant Applicative Forms) in loaded modules is retained
 between evaluations. Turning on <code>+r</code> causes all evaluation of top-level
 expressions to be discarded after each evaluation (they are still
 retained during a single evaluation).
 
 This option may help if the evaluated top-level expressions are
 consuming large amounts of space, or if you need repeatable
 performance measurements.
</blockquote>

Note that it talks about <a href="http://www.haskell.org/haskellwiki/Constant_applicative_form" rel="nofollow noreferrer">constant applicative forms</a>, not functions. However, I couldn't get it to work for your example:

<pre><code>Prelude&gt; :set +r
Prelude&gt; :set +s
Prelude&gt; let f = 1 : map (2*) f
(0.01 secs, 1222216 bytes)
Prelude&gt; last $ show $ f !! 100000
'6'
(3.54 secs, 641914476 bytes)
Prelude&gt; last $ show $ f !! 100000
'6'
(0.04 secs, 1634552 bytes)
Prelude&gt; last $ show $ f !! 100000
'6'
(0.04 secs, 1603568 bytes)
</code></pre>

Apparently, <a href="https://ghc.haskell.org/trac/ghc/ticket/1400" rel="nofollow noreferrer"><code>+r</code> only works for compiled code</a>, though the docs don't mention this.

blocks|key|3881198|text|总而言之，|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3881199|>>>+:set+%2Bs++--+activate+performance+
>>>+:r+++++++--+reset+all+interactive+binding
Ok,+modules+loaded:+none.
>>>+:show+bindings+--+check+the+binding+state|code-block|syntax|javascript|3881200|让我们开始测试|3881201|>>>+let+f+=+1+:+map+(2*)+f
(0.01+secs,+1543272+bytes)
>>>+:show+bindings+
f+::+[Integer]+=+_
>>>+last+$+show+$+f+!!+50000
'6'
(0.55+secs,+170011128+bytes)
>>>+:show+bindings+
f+::+[Integer]+=+1+:+2+:+4+:+8+:+16+:+....
it+::+Char+=+'6'
>>>+last+$+show+$+f+!!+50000
'6'
(0.02+secs,+1562456+bytes)|3881202|使用未定义的，|3881203|>>>+let+f+=+undefined+
(0.01+secs,+565912+bytes)
>>>+:show+bindings+
it+::+Char+=+'6'
f+::+a+=+_
>>>+let+f+=+1+:+map+(2*)+f
(0.01+secs,+513304+bytes)
>>>+last+$+show+$+f+!!+50000
'6'
(0.94+secs,+170517840+bytes)
>>>+:show+bindings+
f+::+[Integer]+=+1+:+2+:+4+:+8+:+16+:+....
it+::+Char+=+'6'|3881204|重置绑定，|3881205|>>>+:r
>>>+:show+bindings+
Ok,+modules+loaded:+none.|3881206|3881207|另一个研究的案例，|3881208|>>>+let+h+=+(2*)
(0.01+secs,+590232+bytes)
>>>+let+f+=+1+:+map+h+f
(0.01+secs,+1138792+bytes)
>>>+:show+bindings+
it+::+Char+=+'6'
h+::+Integer+->+Integer+=+_
f+::+[Integer]+=+_
>>>+last+$+show+$+f+!!+60000
'6'
(1.69+secs,+241802432+bytes)
>>>+last+$+show+$+f+!!+60000
'6'
(0.03+secs,+2002432+bytes)|3881209|仍然缓存，更改h的绑定以查看，|3881210|>>>+let+h+=+(3*)
(0.01+secs,+547208+bytes)
>>>+last+$+show+$+f+!!+60000
'6'
(0.03+secs,+2029592+bytes)
>>>+:show+bindings+
f+::+[Integer]+=+1+:+2+:+4+:+8+:+16+:+....
h+::+Integer+->+Integer+=+_
it+::+Char+=+'6'|3881211|不要紧，也需要重新定义f，|3881212|>>>+let+f+=+1+:+map+h+f
(0.01+secs,+552048+bytes)
>>>+last+$+show+$+f+!!+60000
'1'
(4.36+secs,+374064760+bytes)|3881213|3881214|使用Let+..在...绑定，|3881215|>>>+let+f+=+let+h+=+(2*)+in+1+:+map+h+f
(0.02+secs,+1068272+bytes)
>>>+last+$+show+$+f+!!+60000
'6'
(3.90+secs,+242190168+bytes)
>>>+last+$+show+$+f+!!+60000
'6'
(4.89+secs,+242271560+bytes)
>>>+last+$+show+$+f+!!+60000
'6'
(5.71+secs,+242196976+bytes)
>>>+:show+bindings+
h+::+Integer+->+Integer+=+_
f+::+Num+a+=>+[a]+=+_
it+::+Char+=+'6'|3881216|entityMap^0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|1C|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|1D|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|1E|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|1F|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|1G|8|@]|9|@]|A|$]]|$1|M|3|N|5|D|7|1H|8|@]|9|@]|A|$E|F]]|$1|O|3|P|5|6|7|1I|8|@]|9|@]|A|$]]|$1|Q|3|R|5|D|7|1J|8|@]|9|@]|A|$E|F]]|$1|S|3|-4|5|6|7|1K|8|@]|9|@]|A|$]]|$1|T|3|U|5|6|7|1L|8|@]|9|@]|A|$]]|$1|V|3|W|5|D|7|1M|8|@]|9|@]|A|$E|F]]|$1|X|3|Y|5|6|7|1N|8|@]|9|@]|A|$]]|$1|Z|3|10|5|D|7|1O|8|@]|9|@]|A|$E|F]]|$1|11|3|12|5|6|7|1P|8|@]|9|@]|A|$]]|$1|13|3|14|5|D|7|1Q|8|@]|9|@]|A|$E|F]]|$1|15|3|-4|5|6|7|1R|8|@]|9|@]|A|$]]|$1|16|3|17|5|6|7|1S|8|@]|9|@]|A|$]]|$1|18|3|19|5|D|7|1T|8|@]|9|@]|A|$E|F]]|$1|1A|3|-4|5|6|7|1U|8|@]|9|@]|A|$]]]|1B|$]]

To summarize, 

<pre><code>&gt;&gt;&gt; :set +s -- activate performance 
&gt;&gt;&gt; :r -- reset all interactive binding
Ok, modules loaded: none.
&gt;&gt;&gt; :show bindings -- check the binding state
</code></pre>

Let's start the test,

<pre><code>&gt;&gt;&gt; let f = 1 : map (2*) f
(0.01 secs, 1543272 bytes)
&gt;&gt;&gt; :show bindings 
f :: [Integer] = _
&gt;&gt;&gt; last $ show $ f !! 50000
'6'
(0.55 secs, 170011128 bytes)
&gt;&gt;&gt; :show bindings 
f :: [Integer] = 1 : 2 : 4 : 8 : 16 : ....
it :: Char = '6'
&gt;&gt;&gt; last $ show $ f !! 50000
'6'
(0.02 secs, 1562456 bytes)
</code></pre>

Using undefined, 

<pre><code>&gt;&gt;&gt; let f = undefined 
(0.01 secs, 565912 bytes)
&gt;&gt;&gt; :show bindings 
it :: Char = '6'
f :: a = _
&gt;&gt;&gt; let f = 1 : map (2*) f
(0.01 secs, 513304 bytes)
&gt;&gt;&gt; last $ show $ f !! 50000
'6'
(0.94 secs, 170517840 bytes)
&gt;&gt;&gt; :show bindings 
f :: [Integer] = 1 : 2 : 4 : 8 : 16 : ....
it :: Char = '6'
</code></pre>

reset the binding,

<pre><code>&gt;&gt;&gt; :r
&gt;&gt;&gt; :show bindings 
Ok, modules loaded: none.
</code></pre>

<hr>

Another studie case, 

<pre><code>&gt;&gt;&gt; let h = (2*)
(0.01 secs, 590232 bytes)
&gt;&gt;&gt; let f = 1 : map h f
(0.01 secs, 1138792 bytes)
&gt;&gt;&gt; :show bindings 
it :: Char = '6'
h :: Integer -&gt; Integer = _
f :: [Integer] = _
&gt;&gt;&gt; last $ show $ f !! 60000
'6'
(1.69 secs, 241802432 bytes)
&gt;&gt;&gt; last $ show $ f !! 60000
'6'
(0.03 secs, 2002432 bytes)
</code></pre>

Still cached, change the binding of h to see, 

<pre><code>&gt;&gt;&gt; let h = (3*)
(0.01 secs, 547208 bytes)
&gt;&gt;&gt; last $ show $ f !! 60000
'6'
(0.03 secs, 2029592 bytes)
&gt;&gt;&gt; :show bindings 
f :: [Integer] = 1 : 2 : 4 : 8 : 16 : ....
h :: Integer -&gt; Integer = _
it :: Char = '6'
</code></pre>

Do no matter, need to redefine f also, 

<pre><code>&gt;&gt;&gt; let f = 1 : map h f
(0.01 secs, 552048 bytes)
&gt;&gt;&gt; last $ show $ f !! 60000
'1'
(4.36 secs, 374064760 bytes)
</code></pre>

<hr>

Using Let .. in ... binding,

<pre><code>&gt;&gt;&gt; let f = let h = (2*) in 1 : map h f
(0.02 secs, 1068272 bytes)
&gt;&gt;&gt; last $ show $ f !! 60000
'6'
(3.90 secs, 242190168 bytes)
&gt;&gt;&gt; last $ show $ f !! 60000
'6'
(4.89 secs, 242271560 bytes)
&gt;&gt;&gt; last $ show $ f !! 60000
'6'
(5.71 secs, 242196976 bytes)
&gt;&gt;&gt; :show bindings 
h :: Integer -&gt; Integer = _
f :: Num a =&gt; [a] = _
it :: Char = '6'
</code></pre>

blocks|key|2555848|text|2019年的答案:这是不可能的……|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2555849|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

ANSWER FOR 2019: It's not possible...

GHCI seems to cache the results of functions during an interactive session. It's easy to notice, just call a time-consuming function twice. On the second time, the result will appear immediately.

Is there a way to clear this cache from within GHCI so I don't have to restart it? I'm doing some quick'n'dirty non-detailed performance comparisons, so using System.CPUTime instead would be overkill.

How to clear ghci's function result cache?

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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GHCI似乎在交互式会话期间缓存函数的结果。这很容易注意到，只需调用一个耗时的函数两次。第二次，结果会立即出现。有没有办法从GHCI中清除这个缓存，这样我就不需要重新启动它了？我正在做一些快速的、不详细的性能比较，所以使用System.CPUTime将是一种过度的杀伤力。

问如何清除ghci的函数结果缓存？
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