Example: Failure
lSuppose the input
string is Òa b + cÓ.
lThe parser calls S1(Òa b + cÓ).
lS1 calls V1(Òa b + cÓ).
lV1 identifies a, returns success and unparsed input Òb + cÓ.
lS1 checks for + and does not find it; therefore S1 returns
success, with Òb + cÓ.lSince the top-level call to S1 has returned, but there is residual input, the string is not accepted.
S ¨ V + S | V
V ¨ a | b | c
V ¨ a | b | c