f.hs

-- | Proceed only if there are no errors. Will error out otherwise.
(>|>) :: Comp e a -> Comp e b -> Comp e b
f >|> g = condemn f >> g

-- | Proceed only if there are no errors. Will error out otherwise.
(>|>=) :: Comp e a -> (a -> Comp e b) -> Comp e b
x >|>= f = condemn x >>= f

-- | Sequence only if there are no errors, skips the other action otherwise.
--
-- This is useful for skipping semantic checks that depend on invariants asserted
-- by an earlier pass.
(>?>) :: Comp e a -> Comp e a -> Comp e a
l >?> r = do
  m <- l
  e <- askErrors
  case e of
    [] -> r
    _s -> pure m
    
condemn :: Comp e a -> Comp e a
condemn act = act <* cut

cut :: Comp e ()
cut = do
  e <- askErrors
  case e of
    []  -> pure ()
    _xs -> throwIO BailOut