grammar4.5.lambda, uses lambdas to delegate node creation in a sequence

E	::= S | S + E
S	::= T | P
T	::= F | F * T
P	::= ( E )
F	::= num | id


E	::= S E1
E1	::= E1a | Empty
E1a	::= + E
S	::= T | P
T	::= F T1
T1	::= T1a | Empty
T1a	::= * T
P	::= ( E )
F	::= N | I
N	::= num
I	::= id
