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PO"Overloaded" value constructors
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copied!<p>In <a href="http://learnyouahaskell.com/making-our-own-types-and-typeclasses" rel="nofollow">"Making Our Own Types and Typeclasses"</a> they give the following piece of code : </p> <pre><code>data Point = Point Float Float deriving (Show) data Shape = Circle Point Float | Rectangle Point Point deriving (Show) surface :: Shape -> Float surface (Circle _ r) = pi * r ^ 2 surface (Rectangle (Point x1 y1) (Point x2 y2)) = (abs $ x2 - x1) * (abs $ y2 - y1) nudge :: Shape -> Float -> Float -> Shape nudge (Circle (Point x y) r) a b = Circle (Point (x+a) (y+b)) r nudge (Rectangle (Point x1 y1) (Point x2 y2)) a b = Rectangle (Point (x1+a) (y1+b)) (Point (x2+a) (y2+b)) main = do print (surface (Circle (Point 0 0) 24)) print (nudge (Circle (Point 34 34) 10) 5 10) </code></pre> <p>As it stands the pattern matching against constructors is getting quite cluttered at the point </p> <pre><code>nudge (Rectangle (Point x1 y1) (Point x2 y2)) a b = .... </code></pre> <p>Had we defined the Shape type as : </p> <pre><code>data Shape = Circle Point Float | Rectangle Float Float Float Float deriving (Show) </code></pre> <p>Then even though we lose a bit of clarity into the nature of the type, the patten matching looks less cluttered, as can be seen below : </p> <pre><code>data Point = Point Float Float deriving (Show) data Shape = Circle Point Float | Rectangle Float Float Float Float deriving (Show) surface :: Shape -> Float surface (Circle _ r) = pi * r ^ 2 surface (Rectangle x1 y1 x2 y2) = (abs $ x2 - x1) * (abs $ y2 - y1) nudge :: Shape -> Float -> Float -> Shape nudge (Circle (Point x y) r) a b = Circle (Point (x+a) (y+b)) r nudge (Rectangle x1 y1 x2 y2) a b = Rectangle (x1+a) (y1+b) (x2+a) (y2+b) main = do print (surface (Circle (Point 0 0) 24)) print (nudge (Circle (Point 34 34) 10) 5 10) </code></pre> <p>My question is whether it is possible to have both </p> <pre><code>Rectangle Point Point </code></pre> <p>and </p> <pre><code>Rectangle Float Float Float Float </code></pre> <p>in the same piece of code (i.e. a sort of "overloading" of value constructors), so that we can do something like : </p> <pre><code>... surface (Rectangle (Point x1 y1) (Point x2 y2)) = (abs $ x2 - x1) * (abs $ y2 - y1) ... nudge (Rectangle x1 y1 x2 y2) a b = Rectangle (x1+a) (y1+b) (x2+a) (y2+b) </code></pre> <p>where the "..." denotes the same as in the code above. Also are there any other tricks to make the notation a bit more compact at the "nudge (Rectangle...." point? Thanks</p>

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