1 files changed, 3 insertions, 2 deletions
diff --git a/VM.hs b/VM.hs
index 5f7a818..bed0596 100644
--- a/VM.hs
+++ b/VM.hs
@@ -3,7 +3,6 @@ module VM(vmRun) where
 import Control.Monad
 import Data.Char
 import Data.List
-import Data.Maybe
 import qualified Data.Map.Strict as Map
 import Data.Map.Strict ((!))
 import System.IO
@@ -88,7 +87,9 @@ vmRunTerm info@(Info bbmap _ _) state@(State { sTempMap = tmap }) term = case te
 
 findRef :: TempMap -> Ref -> RunValue
 findRef _ (RConst n) = RVNum n
-findRef tmap (RTemp i) = fromJust (Map.lookup i tmap)
+findRef tmap (RTemp i) = case Map.lookup i tmap of
+                             Nothing -> error "Use of declared but uninitialised variable"
+                             Just v -> v
 findRef _ (RSClo name) = RVClosure name []
 findRef _ RNone = error "VM: None ref used"