pgItem x env ((l, n, w, t):toks)
   | x == w     = POk env toks t
   | otherwise  = PFail (l, n, w, t)
pgItem x env ((l, n, w, t):toks)
   | x == w     = POk env toks t
   | otherwise  = PFail (l, n, w, t)
pgItem x env ((l, n, w, t):toks)
   | x == w     = POk env toks t
   | otherwise  = PFail (l, n, w, t)