hw2: impl interp

hw2/hs/WhileInterp.hs

@@ -1,9 +1,10 @@
 {-
-  Name: <Your name here>
+  Name: Yuri Tatishchev
   Class: CS 252
   Assigment: HW2
-  Date: <Date assignment is due>
-  Description: <Describe the program and what it does>
+  Date: 2026-03-06
+  Description: Implements the big-step operational semantics for
+    the WHILE language described in `while-semantics.pdf`
 -}
 
 
@@ -33,6 +34,8 @@ data Expression =
   | Op Binop Expression Expression
   | If Expression Expression Expression     -- if e1 then e2 else e3
   | While Expression Expression             -- while (e1) e2
+  | BoolOp BoolBinop Expression Expression
+  | Not Expression
   deriving (Show)
 
 data Binop =
@@ -46,6 +49,11 @@ data Binop =
   | Le       -- <= :: Int -> Int -> Bool
   deriving (Show)
 
+data BoolBinop = 
+    And
+  | Or
+  deriving (Show)
+
 data Value =
     IntVal Int
   | BoolVal Bool
@@ -57,17 +65,61 @@ data Value =
 -- Be sure to explicitly check for a divide by 0 and throw an error.
 applyOp :: Binop -> Value -> Value -> Value
 applyOp Plus (IntVal i) (IntVal j) = IntVal $ i + j
-applyOp _ _ _ = error "TBD"
+applyOp Minus (IntVal i) (IntVal j) = IntVal $ i - j
+applyOp Times (IntVal i) (IntVal j) = IntVal $ i * j
+applyOp Divide (IntVal i) (IntVal j) = IntVal $ i `div` j
+applyOp Gt (IntVal i) (IntVal j) = BoolVal $ i > j
+applyOp Ge (IntVal i) (IntVal j) = BoolVal $ i >= j
+applyOp Lt (IntVal i) (IntVal j) = BoolVal $ i < j
+applyOp Le (IntVal i) (IntVal j) = BoolVal $ i <= j
+applyOp _ _ _ = error "Not implemented for non-integer values"
 
+applyBoolOp :: BoolBinop -> Value -> Value -> Value
+applyBoolOp And (BoolVal b1) (BoolVal b2) = BoolVal $ b1 && b2
+applyBoolOp Or (BoolVal b1) (BoolVal b2) = BoolVal $ b1 || b2
+applyBoolOp _ _ _ = error "Not implemented for non-boolean values"
+
+applyNot :: Value -> Value
+applyNot (BoolVal b) = BoolVal $ not b
+applyNot _ = error "Not implemented for non-boolean values"
 
 -- Implement this function according to the specified semantics
 evaluate :: Expression -> Store -> (Value, Store)
+evaluate (Val v) s = (v, s)
+evaluate (Var x) s = case Map.lookup x s of
+  Just v -> (v, s)
+  Nothing -> error "Variable not found"
+evaluate (Assign x e) s =
+  let (v,s') = evaluate e s
+  in (v, Map.insert x v s')
+evaluate (Sequence e1 e2) s =
+  let (_,s1) = evaluate e1 s
+      (v2,s') = evaluate e2 s1
+  in (v2, s')
 evaluate (Op o e1 e2) s =
   let (v1,s1) = evaluate e1 s
       (v2,s') = evaluate e2 s1
   in (applyOp o v1 v2, s')
-evaluate _ _ = error "TBD"
-
+evaluate (If e1 e2 e3) s =
+  let (v1,s1) = evaluate e1 s
+  in case v1 of
+    BoolVal b -> if b then evaluate e2 s1 else evaluate e3 s1
+    _ -> error "Not implemented for non-boolean values"
+evaluate (While e1 e2) s =
+  let (v1,s1) = evaluate e1 s
+  in case v1 of
+    BoolVal b -> if b then
+                   let (_, s2) = evaluate e2 s1
+                   in evaluate (While e1 e2) s2
+                 else (BoolVal False, s1)
+    _ -> error "Not implemented for non-boolean values"
+evaluate (BoolOp o e1 e2) s =
+  let (v1,s1) = evaluate e1 s
+      (v2,s') = evaluate e2 s1
+  in (applyBoolOp o v1 v2, s')
+evaluate (Not e) s =
+  let (v,s') = evaluate e s
+  in (applyNot v, s')
 
 -- Evaluates a program with an initially empty state
 run :: Expression -> (Value, Store)