Hi.
I am testing a winged edge data structure.
module Main where
type Point3 = (Float, Float, Float)
data Body= Body [Vertex] [Edge] [Face] deriving(Eq)
data Face= Face Edge deriving(Eq)
data Edge= Edge (Vertex, Vertex)
(Face, Face)
(Edge, Edge)
(Edge, Edge) deriving(Eq)
data Vertex= Vertex Point3 Edge deriving(Eq)
...
--- Face, Edge, Vertex: Conversion
getVertsFromFace :: Face -> [Vertex]
getVertsFromFace (Face startEdge) = process_wing_clockwise startEdge
where
process_wing_clockwise (Edge
(vp, _)
_
(_, eWing1)
_)
| startEdge == eWing1 =
[vp]
| otherwise =
vp : (process_wing_clockwise eWing1)
--- Misc procedures
printPointList :: [Vertex] -> IO ()
printPointList [] = return ()
printPointList ((Vertex p _ ):vs) = putStr (show p) >>
printPointList vs
--- main
main =
do
let q = createQuad (0,0,0) (0,1,0) (1,1,0) (1,0,0)
let f = (\(Body _ _ (face:faces)) -> face) q
let verts = getVertsFromFace f
printPointList verts
Here I get a error message.
(0.0,0.0,0.0)(0.0,1.0,0.0)(1.0,1.0,0.0)runhugs: Error occurred
ERROR - Control stack overflow
I think this come because the derived Eq-Instance "==" get into an
infinite loop
Alternatively I tried following
--- We want to identify each Body, Face, Edge or Vertex by a number ID
type ID = Int --- A special number for identifying, used for Eq
data Body = Body ID [Vertex] [Edge] [Face]
data Face = Face ID (Edge)
data Edge = Edge ID
(Vertex , Vertex)
(Face , Face)
(Edge , Edge)
(Edge , Edge)
data Vertex = Vertex ID Edge
--- Eq Instances
instance Eq Vertex) where
(Vertex i1 _) == (Vertex i2 _) = i1 == i2
instance Eq Face where
(Face i1 _ ) == (Face i2 _) = i1 == i2
instance Eq Edge where
(Edge i1 _ _ _ _) == (Edge i2 _ _ _ _) = i1 == i2
instance Eq (Body) where
(Body i1 _ _ _) == (Body i2 _ _ _) = i1 == i2
...
This way my code does not hang up. But I have to manage those ugly ID's.
Is there a better way to create instances of class Eq, without something
like ID?
Thanks for reading.
Best regards, Leonard
--------------------
--------------------
---- Begin ----
--------------------
module Main where
type Point3 = (Float, Float, Float)
data Body= Body [Vertex] [Edge] [Face] deriving(Eq)
data Face= Face Edge deriving(Eq)
data Edge= Edge (Vertex, Vertex)
(Face, Face)
(Edge, Edge)
(Edge, Edge) deriving(Eq)
data Vertex= Vertex Point3 Edge deriving(Eq)
{-
implementing simple generative modelling
-}
--- elementar object generation
createQuad :: Point3 ->
Point3 ->
Point3 ->
Point3 ->
Body
createQuad p0 p1 p2 p3 =
let
{faceFront = Face edge0
;faceBack = Face edge2
;vert0 = Vertex p0 edge0
;edge0 = Edge
(vert0, vert1)
(faceFront, faceBack)
(edge3, edge1)
(edge1, edge3)
;vert1 = Vertex p1 edge1
;edge1 = Edge
(vert1, vert2)
(faceFront, faceBack)
(edge0, edge2)
(edge2, edge0)
;vert2 = Vertex p2 edge2
;edge2 = Edge
(vert2, vert3)
(faceFront, faceBack)
(edge1, edge3)
(edge3, edge1)
;vert3 = Vertex p3 edge3
;edge3 = Edge
(vert3, vert0)
(faceFront, faceBack)
(edge2, edge0)
(edge0, edge2)
}
in
Body [vert0, vert1, vert2, vert3] [edge0, edge1, edge2, edge3]
[faceFront, faceBack]
--- Face, Edge, Vertex: Conversion
getVertsFromFace :: Face -> [Vertex]
getVertsFromFace (Face startEdge) = process_wing_clockwise startEdge
where
process_wing_clockwise (Edge
(vp, _)
_
(_, eWing1)
_)
| startEdge == eWing1 =
[vp]
| otherwise =
vp : (process_wing_clockwise eWing1)
--- Misc procedures
printPointList :: [Vertex] -> IO ()
printPointList [] = return ()
printPointList ((Vertex p _ ):vs) = putStr (show p) >>
printPointList vs
--- main
main =
do
let q = createQuad (0,0,0) (0,1,0) (1,1,0) (1,0,0)
let f = (\(Body _ _ (face:faces)) -> face) q
let verts = getVertsFromFace f
printPointList verts
-----------------
---- End ----
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