<div dir="ltr">Thanks I got it now :)<br></div><div class="gmail_extra"><br><div class="gmail_quote">On Thu, Sep 24, 2015 at 9:45 PM, Kostiantyn Rybnikov <span dir="ltr"><<a href="mailto:k-bx@k-bx.com" target="_blank">k-bx@k-bx.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><p dir="ltr">Hi.</p>
<p dir="ltr">Your function gets passed numbers one by one in the place of x, and its previous result in the place of acc, and it returns a Bool. Initial value in place of acc parameter ("previous result") is put as False (since you begin with answer "no" to question "is it elem?").</p>
<p dir="ltr">Hope this helps.<br>
</p>
<div class="gmail_quote">24 вер. 2015 19:04 "goforgit ." <<a href="mailto:teztingit@gmail.com" target="_blank">teztingit@gmail.com</a>> пише:<br type="attribution"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div><div class="h5"><div dir="ltr"><div><div><div><div><div><div><div>Reading <a href="http://learnyouahaskell.com/higher-order-functions" target="_blank">http://learnyouahaskell.com/higher-order-functions</a><br><br></div>I understand that with the function<br><span><span><br><span style="font-family:monospace,monospace">sum'</span></span><span style="font-family:monospace,monospace"><span> :: </span><span>(</span><span>Num</span><span> a)</span><span> => </span><span>[a]</span><span> -> </span><span>a </span></span></span><span style="font-family:monospace,monospace"><br>sum'<span> = </span><span>foldl (+) </span><span>0</span><span><br></span><span><span></span></span></span><br></div><div>the call<br></div><div><br></div>ghci>>> sum' [1,2,3]<br><br></div>will be evaluated as<br><br>0 + 1 + 2 + 3 = 6<br><br></div>But what about the function <span><span><br><br><span style="font-family:monospace,monospace">elem'</span></span><span style="font-family:monospace,monospace"><span> :: </span><span>(</span><span>Eq</span><span> a)</span><span> => </span><span>a</span><span> -> </span><span>[a]</span><span> -> </span><span>Bool</span><span>  <br></span></span></span><span style="font-family:monospace,monospace">elem' y ys<span> = </span><span>foldl (\acc x</span><span> -> </span><span>if</span><span> x</span><span> == </span><span>y </span><span>then</span><span> </span><span>True</span><span> </span><span>else</span><span> acc) </span><span>False</span><span> ys</span></span><br><br></div>and calling it with<br><br></div>ghci>>> elem' 3 [1,2,3]<br><br></div>How is that evaluated to True by foldl in elem'?<br><div><div><div><div><br></div><div>Thanks in advance for any explanation to this!<br></div></div></div></div></div>
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