Give two examples of reasonable semantic rules that cannot be checked at reasonable cost, either statically or by compiler-generated code at run time. Write an S-attributed attribute grammar, based on...

Give two examples of reasonable semantic rules that cannot be checked at reasonable cost, either statically or by compiler-generated code at run time. Write an S-attributed attribute grammar, based on the CFG of Example 4.7, that accumulates the value of the overall expression into the root of the tree. You will need to use dynamic memory allocation so that individual attributes can hold an arbitrary amount of information.