Explain the need for the A:B notation on the left-hand sides of productions in a tree grammar. Why isn’t similar notation required for context-free grammars? A potential objection to the tree...

Explain the need for the A:B notation on the left-hand sides of productions in a tree grammar. Why isn’t similar notation required for context-free grammars? A potential objection to the tree attribute grammar of Example 4.17 is that it repeatedly copies the entire symbol table from one node to another. In this particular tiny language, it is easy to see that the referencing environment never shrinks: the symbol table changes only with the addition of new identifiers. Exploiting this observation, show how to modify the pseudocode of Figure 4.14 so that it copies only pointers, rather than the entire symbol table.