CS536 Homework 7 Solution

Question 1:

The following productions need to be added to the Wumbo grammar:

typedef → TYPEDEF STRUCT ID ID SEMICOLON
type → ID
varDeclList → varDeclList typedef

The first production permits typedefs to be used with struct types. The second production permits a declaration that uses a new type name. The third production permits a typedef to occur anywhere that a local variable declaration can occur.

Question 2:

1. Each symbol table entry should include "kind" (variable, function, struct,or typedef) information, as well as "type" information. For a typedef, the "type" information is the built-in type or struct type for which the typedef defines a new name. (Note: It is also possible to let the "type" field be a typedef name, but that complicates type checking. Note also that if the "kind" field is not needed for type checking, then it is OK just to have a flag that says whether or not this is a typedef name.)

2. To process typedef T xxx:

   • If T is an ID (rather than a built-in type or a struct type), then do a global lookup on T. If it is not found, or its "kind" is not "typedef", then give an error message.
   • Do a local lookup on xxx. If found, give an error message (multiply declared name).
   • If no errors, add the name xxx to the current symbol table with kind = typedef. If T is a built-in or struct type, then use that type for the "type" field of the symbol-table entry; otherwise, use the value from the "type" field of T's symbol-table entry.

3. To process a use of name xxx in a statement:

   • Do a global lookup of xxx as usual.
   • If not found: error (use of undeclared name).
   • If found and "kind" = typedef: error (note: this step could be omitted here, and this kind of error could be handled as part of type checking).
   • If no errors, link use to corresponding declaration (as usual).

4. Processing a variable/function/parameter declaration T xxx is the same as processing typedef T xxx except that when xxx is added to the symbol table, its kind is var/function/parameter (as appropriate) instead of "typedef".

Here is the symbol table after processing the given declarations: