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copied!<p>It means exactly what the error says. You have specified that the type of your function is</p> <pre><code>divideby :: ( Int->Int -> Int ) -> Int ->float </code></pre> <p>That means, the first argument must be a function, with the type <code>Int->Int -> Int</code>, and the second input must be an <code>Int</code>, and then it will produce a <code>float</code>. Naturally, Haskell does not know how to divide a function by an Int, which is what you are telling it to do with the expression <code>f / z</code>.</p> <hr> <p>In response to the comment: no. That is not a higher-order function, but it is close. Take a look:</p> <pre><code>addNum :: Int -> Int -> Int addNum a b = a + b divideBy :: Int -> Int -> Int -> Int divideBy a b c = (addNum a b) `div` c </code></pre> <p><code>divideBy</code> is a function that takes 3 <code>Int</code>s as input, and produces an <code>Int</code>. Since its inputs are merely <code>Int</code>, it is <em>not</em> a higher-order function. However, you could abstract the use of <code>addNum</code> into an input, thus making it a higher-order function. <code>addNum</code> has type <code>(Int -> Int -> Int)</code>, so, in addition to the inputs we have already, we will make that the type of our first input</p> <pre><code>divideBy :: (Int -> Int -> Int) -> Int -> Int -> Int -> Int divideBy f a b c = (f a b) `div` c </code></pre> <p><em>This</em> is a higher-order function, that also compiles correctly and has meaning. :) You can pass <code>addNum</code> as an input to this function.</p> <pre><code>ghci> divideBy addNum 2 4 6 -- (2 + 4) / 6 1 </code></pre>

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