<div dir="ltr"><div>Hello Emanuel,<br><br></div><div>Here's the excerpt of the "reverse" function in GHC-List (<br><br><pre><a name="line-414"></a><a name="reverse"></a><span class="">-- | 'reverse' @xs@ returns the elements of @xs@ in reverse order.</span>
<a name="line-415"></a><span class="">-- @xs@ must be finite.</span>
<a name="line-416"></a><span class="">reverse</span> <span class="">::</span> <span class="">[</span><span class="">a</span><span class="">]</span> <span class="">-></span> <span class="">[</span><span class="">a</span><span class="">]</span>
<a name="line-417"></a><span class="">#ifdef USE_REPORT_PRELUDE</span>
<a name="line-418"></a><span class="">reverse</span> <span class="">=</span> <span class="">foldl</span> <span class="">(</span><span class="">flip</span> <span class="">(</span><span class="">:</span><span class="">)</span><span class="">)</span> <span class="">[]</span>
<a name="line-419"></a><span class="">#else</span>
<a name="line-420"></a><span class="">reverse</span> <span class="">l</span> <span class="">=</span> <span class="">rev</span> <span class="">l</span> <span class="">[]</span>
<a name="line-421"></a> <span class="">where</span>
<a name="line-422"></a> <span class="">rev</span> <span class="">[]</span> <span class="">a</span> <span class="">=</span> <span class="">a</span>
<a name="line-423"></a> <span class="">rev</span> <span class="">(</span><span class="">x</span><span class="">:</span><span class="">xs</span><span class="">)</span> <span class="">a</span> <span class="">=</span> <span class="">rev</span> <span class="">xs</span> <span class="">(</span><span class="">x</span><span class="">:</span><span class="">a</span><span class="">)</span>
<a name="line-424"></a><span class="">#endif</span><span class=""><br><br></span></pre><pre><span class="">Reversing an infinite list, Haskell will try to reach the end of the list until it runs out of memory.<br>I don't thing it's doable lazily.<br>
</span></pre><br></div><div><div><div class="gmail_extra"><br><br><div class="gmail_quote">On Tue, Dec 18, 2012 at 9:24 AM, Emanuel Koczwara <span dir="ltr"><<a href="mailto:poczta@emanuelkoczwara.pl" target="_blank">poczta@emanuelkoczwara.pl</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">Hi,<br>
<br>
When I run this code in ghci:<br>
<br>
reverse [1..]<br>
<br>
I get:<br>
<br>
<interactive>: out of memory (requested 2097152 bytes)<br>
<br>
Can anyone explain this behaviour?<br>
<br>
Emanuel<br>
<br>
<br>
<br>
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</blockquote></div><br></div></div></div></div>