1 files changed, 13 insertions, 2 deletions
diff --git a/vm.hs b/vm.hs
index 04de0c5..b3b19e4 100644
--- a/vm.hs
+++ b/vm.hs
@@ -5,6 +5,7 @@ import Data.List
 import Data.Maybe
 import qualified Data.Map.Strict as Map
 import Data.Map.Strict ((!))
+import System.IO
 import qualified System.IO.Error as IO
 import Debug.Trace
 
@@ -28,6 +29,7 @@ data RunValue
     | RVNum Int
     | RVString String
     | RVQuoted RunValue
+    | RVName Name
   deriving Show
 
 kErrorExit :: String
@@ -101,8 +103,12 @@ vmRunBuiltin "print" as = putStrLn (intercalate ", " (map printshow as)) >> retu
 vmRunBuiltin "<=" [RVNum a, RVNum b] = return (RVNum (fromEnum (a <= b)))
 vmRunBuiltin "+" [RVNum a, RVNum b] = return (RVNum (a + b))
 vmRunBuiltin "-" [RVNum a, RVNum b] = return (RVNum (a - b))
-vmRunBuiltin "car" [RVList (a:_)] = return a
-vmRunBuiltin "cdr" [RVList (_:a)] = return (RVList a)
+vmRunBuiltin "car" [RVList l] = case l of
+    a : _ -> return a
+    _ -> throw "Empty list in 'car'"
+vmRunBuiltin "cdr" [RVList l] = case l of
+    _ : a -> return (RVList a)
+    _ -> throw "Empty list in 'cdr'"
 vmRunBuiltin "list" values = return (RVList values)
 vmRunBuiltin name args = error (name ++ " " ++ show args)
 
@@ -112,6 +118,7 @@ printshow (RVList values) = show values
 printshow (RVNum i) = show i
 printshow (RVQuoted value) = '\'' : show value
 printshow (RVClosure _ _) = "[closure]"
+printshow (RVName name) = name
 
 truthy :: RunValue -> Bool
 truthy (RVNum n) = n /= 0
@@ -122,4 +129,8 @@ toRunValue (VList values) = RVList (map toRunValue values)
 toRunValue (VNum i) = RVNum i
 toRunValue (VString s) = RVString s
 toRunValue (VQuoted value) = RVQuoted (toRunValue value)
+toRunValue (VName name) = RVName name
 toRunValue _ = undefined
+
+throw :: String -> IO a
+throw s = hPutStrLn stderr s >> IO.ioError (IO.userError kErrorExit)