completed chapter 5 of the book

src/09-pattern-matching/PatMat.purs

@@ -0,0 +1,55 @@
+module PatMat where
+
+import Prelude
+
+import Data.Maybe (Maybe(..))
+
+fact :: Int -> Int
+fact 0 = 0
+fact 1 = 1
+fact n = n * fact (n - 1)
+
+binCoeff :: Int -> Int -> Int
+binCoeff n 0 = 1
+binCoeff n k 
+  | n == k = 1
+  | n > k && k > 0 = binCoeff (n - 1) (k -1) + binCoeff (n - 1) k
+binCoeff _ _ = 0
+
+sameCity :: { city :: String } -> { city :: String } -> Boolean
+sameCity p1 p2 = p1.city == p2.city
+
+fromSingleton :: forall a. a -> Array a -> a
+fromSingleton default [x] = x
+fromSingleton default _ = default 
+
+-- chapter 5.12
+data Shape
+  = Circle Point Number
+  | Rectangle Point Number Number
+  | Line Point Point
+  | Text Point String
+
+data Point = Point
+  { x :: Number
+  , y :: Number
+  }
+
+origin :: Point
+origin = Point { x, y }
+  where
+    x = 0.0
+    y = 0.0
+
+defaultCircle :: Shape
+defaultCircle = Circle origin 10.0
+
+getText :: Shape -> Maybe String
+getText (Text _ t) = Just t
+getText _ = Nothing
+
+sortPair :: Array Int -> Array Int
+sortPair arr@[x, y]
+  | x <= y = arr
+  | otherwise = [y, x]
+sortPair arr = arr