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copied!<p>The key to understanding currying is to understand that there is no such thing as a function with more than one argument. <em>Every</em> function in haskell has exactly one argument. But because of the right-associative properties of the <code>-></code> operator, that's not immediately clear. </p> <p>When you see this: </p> <pre><code>Integer -> Integer -> Integer </code></pre> <p>It is equivalent to this:</p> <pre><code>Integer -> (Integer -> Integer) </code></pre> <p>In both cases, the function takes an <code>Integer</code> and <em>returns a function</em>. (The function returned is one that takes an <code>Integer</code> and returns an <code>Integer</code>.) So this might be something like a simple mathematical operation; it takes an <code>Integer</code> (let's say 5) and returns a function that takes another <code>Integer</code> (5 again) and adds it to the first one, and returns the result (10). </p> <p>But when you do this:</p> <pre><code>(Integer -> Integer) -> Integer </code></pre> <p>You've created something very different -- a function that <em>takes</em> a function and returns an <code>Integer</code>. This could also be a way of implementing a mathematical function; but instead of taking an <code>Integer</code> as the first argument, it takes the mathematical operation itself! So for example, say you pass to this function a function that adds 5 to whatever is passed to it. This function then passes <code>5</code> to <em>that</em> function, and returns the result (10). </p>

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