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POHaskell type enforcement on typeclass parameters
 

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    <p>I am trying to follow along a machine learning book and knowing a bit about the future content I am trying make my code generalisable.</p> <p>Here is my code. I will eventually have other instances of DataSet, but this is all I have for now.</p> <pre><code>data SupervisedDataSet x y = SupervisedDataSet [([x], y)] deriving (Show) class DataSet a where augment :: x -&gt; a -&gt; a --Augment each input vector, making x the head. instance DataSet (SupervisedDataSet x y) where augment v (SupervisedDataSet ds) =· let xsys = unzip ds in SupervisedDataSet $ zip (map (v:) $ fst xsys) (snd xsys) </code></pre> <p>I am trying to enforce the type of the first parameter of <code>SupervisedDataSet</code> with the first parameter of <code>augment</code> as requested by the type checker in GHC.</p> <pre><code>Perceptron.hs:16:7: Couldn't match type `x1' with `x' `x1' is a rigid type variable bound by the type signature for agument :: x1 -&gt; SupervisedDataSet x y -&gt; SupervisedDataSet x y at Perceptron.hs:14:3 `x' is a rigid type variable bound by the instance declaration at Perceptron.hs:13:37 Expected type: SupervisedDataSet x1 y Actual type: SupervisedDataSet x y In the expression: SupervisedDataSet $ zip (map (v :) $ fst xsys) (snd xsys) In the expression: let xsys = unzip ds in SupervisedDataSet $ zip (map (v :) $ fst xsys) (snd xsys) </code></pre> <p>I understand why I am receiving the error, I just don't know how to fix it. Any ideas would be appreciated. Thanks</p> <p>Thanks for your time.</p>
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