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|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|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。

文章

问答

视频

学习中心

腾讯云实验室

直播

竞赛

腾讯云代码分析专区

腾讯iOA零信任安全管理系统专区

腾讯云架构师技术同盟交流圈

腾讯云数据库专区

腾讯云顾问专区

腾讯云原生专区

腾讯混元专区

腾讯云TCE专区

腾讯云Lighthouse专区

腾讯云HAI专区

腾讯云Edgeone专区

腾讯云存储专区

腾讯云智能专区

腾讯轻联专区 

腾讯云开发专区

TAPD专区

腾讯轻量云游戏服专区

腾讯云最具价值专家

腾讯云架构师技术同盟

腾讯云创作之星

腾讯云开发者先锋

腾讯云代码助手

云原生构建

TAPD 敏捷项目管理

Cloud Studio

SDK中心

API中心

命令行工具

涵盖代码开发、场景应用、自动测试全流程，助你从零构建专属AI助手

一站式MCP教程库，解锁AI应用新玩法

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？
EN

Stack Overflow用户

社区

活动

圈层

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问如何清除ghci的函数结果缓存？EN