A CFG-based attribute evaluator capable of handling non-L-attributed attribute flow needs to take a parse tree as input. Explain how to build a parse tree automatically during a top-down or bottom-up...

A CFG-based attribute evaluator capable of handling non-L-attributed attribute flow needs to take a parse tree as input. Explain how to build a parse tree automatically during a top-down or bottom-up parse (i.e., without explicit action routines). Building on Example 4.13, modify the remainder of the recursive descent parser of Figure 2.17 to build syntax trees for programs in the calculator language.