valB (a :||: b)  s st | evalB a s st = (True,st)
                       | otherwise = evalB b s st

evalB (a :||: b)  s st | evalB a s st = (True,st)
                       | otherwise = evalB b s st
evalB (a :||: b)  s st | evalB a s st = (True,st)
                       | otherwise = evalB b s st