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POHaskell Zipper for ADT with many constructors
 

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  1. POHaskell Zipper for ADT with many constructors
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    <p>I have a few ADT's that represent a simple geometry tree in Haskell. Something about having my operation types separate from the tree structure is bothering me. I'm thinking of making the Tree type contain constructors for the operators,it just seems like it would be cleaner. One problem I see with this is that my Zipper implementation will have to change to reflect all these new possible constructors. Is there any way around this? Or am I missing some important concept? In general I feel like I'm having trouble getting a grip on how to generally structure my programs in Haskell. I understand most of the concepts, ADT's, type classes, monads, but I'm not understanding the big picture yet. Thanks.</p> <pre><code>module FRep.Tree (Tree(‥) ,Primitive(‥) ,UnaryOp(‥) ,BinaryOp(‥) ,TernaryOp(‥) ,sphere ,block ,transform ,union ,intersect ,subtract ,eval ) where import Data.Vect.Double --import qualified Data.Foldable as F import Prelude hiding (subtract) --import Data.Monoid data Tree = Leaf Primitive | Unary UnaryOp Tree | Binary BinaryOp Tree Tree | Ternary TernaryOp Tree Tree Tree deriving (Show) sphere ∷ Double → Tree sphere a = Leaf (Sphere a) block ∷ Vec3 → Tree block v = Leaf (Block v) transform ∷ Proj4 → Tree → Tree transform m t1 = Unary (Transform m) t1 union ∷ Tree → Tree → Tree union t1 t2 = Binary Union t1 t2 intersect ∷ Tree → Tree → Tree intersect t1 t2 = Binary Intersect t1 t2 subtract ∷ Tree → Tree → Tree subtract t1 t2 = Binary Subtract t1 t2 data Primitive = Sphere { radius ∷ Double } | Block { size ∷ Vec3 } | Cone { radius ∷ Double , height ∷ Double } deriving (Show) data UnaryOp = Transform Proj4 deriving (Show) data BinaryOp = Union | Intersect | Subtract deriving (Show) data TernaryOp = Blend Double Double Double deriving (Show) primitive ∷ Primitive → Vec3 → Double primitive (Sphere r) (Vec3 x y z) = r - sqrt (x*x + y*y + z*z) primitive (Block (Vec3 w h d)) (Vec3 x y z) = maximum [inRange w x, inRange h y, inRange d z] where inRange a b = abs b - a/2.0 primitive (Cone r h) (Vec3 x y z) = undefined unaryOp ∷ UnaryOp → Vec3 → Vec3 unaryOp (Transform m) v = trim (v' .* (fromProjective (inverse m))) where v' = extendWith 1 v ∷ Vec4 binaryOp ∷ BinaryOp → Double → Double → Double binaryOp Union f1 f2 = f1 + f2 + sqrt (f1*f1 + f2*f2) binaryOp Intersect f1 f2 = f1 + f2 - sqrt (f1*f1 + f2*f2) binaryOp Subtract f1 f2 = binaryOp Intersect f1 (negate f2) ternaryOp ∷ TernaryOp → Double → Double → Double → Double ternaryOp (Blend a b c) f1 f2 f3 = undefined eval ∷ Tree → Vec3 → Double eval (Leaf a) v = primitive a v eval (Unary a t) v = eval t (unaryOp a v) eval (Binary a t1 t2) v = binaryOp a (eval t1 v) (eval t2 v) eval (Ternary a t1 t2 t3) v = ternaryOp a (eval t1 v) (eval t2 v) (eval t3 v) --Here's the Zipper-------------------------- module FRep.Tree.Zipper (Zipper ,down ,up ,left ,right ,fromZipper ,toZipper ,getFocus ,setFocus ) where import FRep.Tree type Zipper = (Tree, Context) data Context = Root | Unary1 UnaryOp Context | Binary1 BinaryOp Context Tree | Binary2 BinaryOp Tree Context | Ternary1 TernaryOp Context Tree Tree | Ternary2 TernaryOp Tree Context Tree | Ternary3 TernaryOp Tree Tree Context down ∷ Zipper → Maybe (Zipper) down (Leaf p, c) = Nothing down (Unary o t1, c) = Just (t1, Unary1 o c) down (Binary o t1 t2, c) = Just (t1, Binary1 o c t2) down (Ternary o t1 t2 t3, c) = Just (t1, Ternary1 o c t2 t3) up ∷ Zipper → Maybe (Zipper) up (t1, Root) = Nothing up (t1, Unary1 o c) = Just (Unary o t1, c) up (t1, Binary1 o c t2) = Just (Binary o t1 t2, c) up (t2, Binary2 o t1 c) = Just (Binary o t1 t2, c) up (t1, Ternary1 o c t2 t3) = Just (Ternary o t1 t2 t3, c) up (t2, Ternary2 o t1 c t3) = Just (Ternary o t1 t2 t3, c) up (t3, Ternary3 o t1 t2 c) = Just (Ternary o t1 t2 t3, c) left ∷ Zipper → Maybe (Zipper) left (t1, Root) = Nothing left (t1, Unary1 o c) = Nothing left (t1, Binary1 o c t2) = Nothing left (t2, Binary2 o t1 c) = Just (t1, Binary1 o c t2) left (t1, Ternary1 o c t2 t3) = Nothing left (t2, Ternary2 o t1 c t3) = Just (t1, Ternary1 o c t2 t3) left (t3, Ternary3 o t1 t2 c) = Just (t2, Ternary2 o t1 c t3) right ∷ Zipper → Maybe (Zipper) right (t1, Root) = Nothing right (t1, Unary1 o c) = Nothing right (t1, Binary1 o c t2) = Just (t2, Binary2 o t1 c) right (t2, Binary2 o t1 c) = Nothing right (t1, Ternary1 o c t2 t3) = Just (t2, Ternary2 o t1 c t3) right (t2, Ternary2 o t1 c t3) = Just (t3, Ternary3 o t1 t2 c) right (t3, Ternary3 o t1 t2 c) = Nothing fromZipper ∷ Zipper → Tree fromZipper z = f z where f ∷ Zipper → Tree f (t1, Root) = t1 f (t1, Unary1 o c) = f (Unary o t1, c) f (t1, Binary1 o c t2) = f (Binary o t1 t2, c) f (t2, Binary2 o t1 c) = f (Binary o t1 t2, c) f (t1, Ternary1 o c t2 t3) = f (Ternary o t1 t2 t3, c) f (t2, Ternary2 o t1 c t3) = f (Ternary o t1 t2 t3, c) f (t3, Ternary3 o t1 t2 c) = f (Ternary o t1 t2 t3, c) toZipper ∷ Tree → Zipper toZipper t = (t, Root) getFocus ∷ Zipper → Tree getFocus (t, _) = t setFocus ∷ Tree → Zipper → Zipper setFocus t (_, c) = (t, c) </code></pre>
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      1. POHaskell Zipper for ADT with many constructors
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    1. COIt would be much better if you'd provide a code sample that works.
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    2. COIndeed, unicode characters like `∷` instead `::` and missing datatypes makes it complicated to do anything with that. Could you provide a code sample that can be compiled right away?
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    3. COJust add `{-# LANGUAGE UnicodeSyntax #-}` or search-replace the operators...
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