🚀 Functions

a1/src/APL/Eval.hs

@@ -11,6 +11,7 @@ import APL.AST (Exp (..), VName)
 data Val
   = ValInt Integer
   | ValBool Bool
+  | ValFun Env VName Exp
   deriving (Eq, Show)
 
 type Env = [(VName, Val)]
@@ -78,5 +79,13 @@ eval env (Let var e1 e2) =
   case eval env e1 of
     Left err -> Left err
     Right v -> eval (envExtend var v env) e2
+eval env (Lambda var e) = Right $ ValFun env var e
+eval env (Apply e1 e2) =
+  case (eval env e1, eval env e2) of
+    (Left err, _) -> Left err
+    (_, Left err) -> Left err
+    (Right (ValFun env2 var e3), Right x)   -> eval (envExtend var x env2) e3
+    (_, _)                                  -> Left "Applying non-function"
+
 
 -- TODO: Add cases after extending Exp.