Chapter 7

1. Type checking finds many errors that would prevent the program from running correctly. But it also helps determine how much memory will be needed to hold variables, and exactly what instructions will be needed to perform the various operations in the program.
2. A structure type is needed to represent arbitrarily deep composite structures, including recursive structures such as linked lists. Any given program only has a finite number of such types, so it would be possible to enumerate them and represent them using integer subscripts by placing them in a type table, but references to structures provide a more direct representation.
3. If real compilers reported an OK line for every successful type check, non-toy programs would emit thousands of such checks on every compile, making it difficult to notice the occasional errors.
4. Picky type checkers may be a pain for programmers, but they help avoid unintended type conversions that hide logic errors, and they also reduce...