POLYGON: add polygon module

Algebra/Polygon.hs

@@ -0,0 +1,26 @@
+{-# OPTIONS_HADDOCK ignore-exports #-}
+
+module Algebra.Polygon where
+
+import Algebra.Vector
+import MyPrelude
+{- import Diagrams.Coordinates -}
+
+
+splitPoly :: [PT]
+          -> Segment
+          -> [[PT]]
+splitPoly pts (a, b)
+  | elem a pts && elem b pts =
+    [b : takeWhile (/= b) shiftedPoly, a : dropWhile (/= b) shiftedPoly]
+  | otherwise = [[]]
+    where
+      shiftedPoly = shiftM' a pts
+
+
+polySegments :: [PT] -> [Segment]
+polySegments p@(x':_:_:_) = go p ++ [(last p, x')]
+  where
+    go (x:y:xs) = (x, y) : go (y:xs)
+    go _        = []
+polySegments _ = []

CG2.cabal

@@ -54,7 +54,8 @@ executable Gtk
   main-is:             GtkMain.hs
 
   -- Modules included in this executable, other than Main.
-  other-modules:       Algebra.Vector
+  other-modules:       Algebra.Polygon
+                       Algebra.Vector
                        Algorithms.GrahamScan
                        Algorithms.PolygonIntersection
                        Algorithms.PolygonTriangulation
@@ -103,7 +104,8 @@ executable Gif
   main-is:             GifMain.hs
 
   -- Modules included in this executable, other than Main.
-  other-modules:       Algebra.Vector
+  other-modules:       Algebra.Polygon
+                       Algebra.Vector
                        Algorithms.GrahamScan
                        Algorithms.PolygonIntersection
                        Algorithms.PolygonTriangulation
@@ -149,7 +151,8 @@ executable Test
   main-is:             TestMain.hs
 
   -- Modules included in this executable, other than Main.
-  other-modules:       Algebra.Vector
+  other-modules:       Algebra.Polygon
+                       Algebra.Vector
                        Algorithms.GrahamScan
                        Algorithms.PolygonIntersection
                        Algorithms.PolygonTriangulation