🕸️ Try-Catch

a1/src/APL/AST.hs

@@ -21,6 +21,7 @@ data Exp
   | Let VName Exp Exp
   | Lambda VName Exp
   | Apply Exp Exp
+  | TryCatch Exp Exp
   deriving (Eq, Show)
 
 printExp :: Exp -> String

a1/src/APL/Eval.hs

@@ -86,6 +86,8 @@ eval env (Apply e1 e2) =
     (_, Left err) -> Left err
     (Right (ValFun env2 var e3), Right x)   -> eval (envExtend var x env2) e3
     (_, _)                                  -> Left "Applying non-function"
+eval env (TryCatch e1 e2) =
+  case (eval env e1) of
+    (Right x) -> Right x
+    (Left _) -> eval env e2
 
-
--- TODO: Add cases after extending Exp.

a1/src/APL/Eval_Tests.hs

@@ -102,5 +102,11 @@ tests =
         eval [] (Apply (Let "x" (CstInt 2) (Lambda "y" (Add (Var "x") (Var "y")))) (CstInt 3))
         @?= Right (ValInt 5),
       testCase "Apply (fact)" $
-        eval envEmpty (Apply fact (CstInt 5)) @?= Right (ValInt 120)
+        eval envEmpty (Apply fact (CstInt 5)) @?= Right (ValInt 120),
+      testCase "Try" $
+        eval envEmpty (TryCatch (CstInt 0) (CstInt 1))
+        @?= Right (ValInt 0),
+      testCase "Catch" $
+        eval envEmpty (TryCatch (Var "missing") (CstInt 1))
+        @?= Right (ValInt 1)
     ]