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POHaskell, Even though my type is not specified I get this error: Couldn't match type `a' with `[a]', `a' is a rigid type variable bound by
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copied!<p>So I realize this is a possible duplicate question, as there a number of those errors reported on Stack Overflow, but none of the solutions seem to apply to my problem.</p> <p>So I have the following function:</p> <pre><code>elementAt' :: Integral b => [a] -> b -> a elementAt' [x:_] 1 = x elementAt' [x:xs] y = elementAt' xs yminus1 where yminus1 = y - 1 </code></pre> <p>In case you're wondering it's problem 3 from <a href="http://haskell.org/haskellwiki/H-99%3a_Ninety-Nine_Haskell_Problems">99 Haskell Problems</a>. The goal of the function is to take as input a list and an index, and return the value at that index (starting at 1). I don't want a solution to the problem, if I did I could just look at the ones provided. But I'm getting an error I don't understand. I'm using eclipseFP, the eclipse plugin for haskell and it's underlining the "[x:_]" and "[x:xs]" portions of the function with the following error:</p> <pre><code>Couldn't match type `a' with `[a]' `a' is a rigid type variable bound by the type signature for elementAt' :: Integral b => [a] -> b -> a </code></pre> <p>In all the threads that discuss this error that I've looked at the problem usually occurs when someone tries to give an incorrect output to something which expects a certain type. For example, returning the length of something (which is of type Int) to what should be a "Num a" variable type.</p> <p>But in my case I'm not even providing a type for variable a. It should be able to be ANYTHING, right? So why am I getting this error? If I understood why I was getting the error I could fix it, but I just don't understand.</p> <p>Could someone please explain to me why I'm receiving this error?</p> <p>Your help is much appreciated, thank you. -Asaf</p> <p>Edit: Every answer provided so far is correct, thank you all for the helpful information. I'm going to pick the one I believe to be most clear (I have to wait 5 minutes to do it though).</p>

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