1 files changed, 1 insertions, 1 deletions

diff --git a/src/Sequence/Formula.hs b/src/Sequence/Formula.hs
index 7fb4ccb..e860c53 100644
--- a/src/Sequence/Formula.hs
+++ b/src/Sequence/Formula.hs
@@ -80,7 +80,7 @@ evalFormula = evalFormula' []
 
 val :: Integral a => Traversal' input (Formula input) -> String -> Bool -> Formula input
 val answer prompt keepResult = do
-  gets (Set.member prompt) >>= bool (modify $ Set.insert prompt) (throwError Question{..})
+  gets (Set.member prompt) >>= bool (modify $ Set.insert prompt) (modify (Set.delete prompt) >> throwError Question{..})
   preview answer >>= maybe (throwError Question{..}) id
 
 -- viewL :: Lens' lInput sInput -> Prism' (FormulaM sInput a) (FormulaM lInput a)