Precedence is an integer in the range 1 to 1200.
Associativity must be one of the atoms
xfx, xfy, yfx, fx, fy, xf, yf.
Success: current_op(300, fx, *). [eclipse]: current_op(P, A, +). P = 500 A = fx More? (;) P = 500 A = yfx More? (;) % RETURN pressed yes. Fail: current_op(10, fx, noop). Error: current_op(prec, fx, +). (Error 5). current_op(100, fff, +). (Error 5). current_op(100, fx, bad(op)). (Error 5). current_op(-1, fx, +). (Error 6).