/* E -> E + T | T
   T -> T * F | F
   F -> a | ( E )
*/

:-table e/3,t/3.
e(E+T) --> e(E), [+], t(T).
e(T) --> t(T).

t(T*F) --> t(T), [*], f(F).
t(F) --> f(F).

f(a) --> [a].
f((E)) --> ['('], e(E), [')'].