/* Example of definite clause grammar, as given on the class handout */

expr(Z) --> term(Z).
expr(Z) --> term(X),"+",expr(Y),{Z is X+Y}.
expr(Z) --> term(X),"-",expr(Y),{Z is X-Y}.

term(Z) --> number(Z).
term(Z) --> number(X),"*",term(Y),{Z is X*Y}.
term(Z) --> number(X),"/",term(Y),{Z is X/Y}.

number(X) --> [C],{48=<C,C=<57,X is C-48}.
number(C) --> "+",number(C).
number(C) --> "-",number(X),{C is -X}.