add fourth exercise of lecture 5HEADmaster

1 files changed, 35 insertions, 0 deletions

diff --git a/lec05/Calc.hs b/lec05/Calc.hs
index f97d784..7502b5f 100644
--- a/lec05/Calc.hs
+++ b/lec05/Calc.hs
@@ -31,3 +31,38 @@ instance Expr ExprT where
 
 reify :: ExprT -> ExprT
 reify = id
+
+-- Exercise 4
+
+instance Expr Integer where
+         lit x   = x
+         add l r = eval (Add (Lit l) (Lit r))
+         mul l r = eval (Mul (Lit l) (Lit r))
+
+instance Expr Bool where
+         lit x
+             | x <= 0    = False
+             | otherwise = True
+         add = (||)
+         mul = (&&)
+
+newtype MinMax = MinMax Integer deriving (Eq, Show)
+newtype Mod7   = Mod7 Integer deriving (Eq, Show)
+
+instance Expr MinMax where
+         lit = MinMax
+         add (MinMax l) (MinMax r) = MinMax (max l r)
+         mul (MinMax l) (MinMax r) = MinMax (min l r)
+
+instance Expr Mod7 where
+         lit x = Mod7 (mod x 7)
+         add (Mod7 l) (Mod7 r) = Mod7 (mod (l + r) 7)
+         mul (Mod7 l) (Mod7 r) = Mod7 (mod (l * r) 7)
+
+testExp :: Expr a => Maybe a
+testExp = parseExp lit add mul "(3 * -4) + 5"
+
+testInteger = testExp :: Maybe Integer
+testBool    = testExp :: Maybe Bool
+testMM      = testExp :: Maybe MinMax
+testSat     = testExp :: Maybe Mod7