Add circle sweeping for torus

.ghci

@@ -0,0 +1 @@
+:set prompt "ghci> "

donut-hs.cabal

@@ -9,6 +9,7 @@ build-type:          Simple
 
 executable donut-hs
   main-is:             Main.hs
+  other-modules:       Data.Vector
   build-depends:       base >=4.14 && <4.15
   hs-source-dirs:      src
   default-language:    Haskell2010

src/Data/Vector.hs

@@ -0,0 +1,13 @@
+module Data.Vector 
+( Vector(Vector) ) where
+
+data Vector a = Vector a a a
+    deriving (Show, Eq)
+
+instance (Num a) => Num (Vector a) where
+  (Vector x1 y1 z1) + (Vector x2 y2 z2) = Vector (x1+x2) (y1+y2) (z1+z2)
+  (*) = undefined
+  abs = undefined
+  signum = undefined
+  fromInteger = undefined
+  negate = undefined

src/Main.hs

@@ -1,4 +1,22 @@
 module Main where
 
+import Data.Vector
+
+_r :: Float
+_r = 1.0
+_R :: Float
+_R = 2.0
+
+drawCircle :: Vector Float -> [Vector Float]
+drawCircle center = map ((+) center . vradius) [0,0.1..2*pi] 
+  where 
+    vradius :: Float -> Vector Float
+    vradius theta = Vector (_r * cos theta) (_r * sin theta) 0
+
+render :: [[Char]]
+render = ["hello", "world"]
+
 main :: IO ()
-main = putStrLn "Hello, Haskell!"
+main = do
+  let screen = unlines render
+  putStr screen