ProblemSet4.txt

			Last revised 23-Feb-15

			    Problem Set 4

		 Harvard Extension School CSCI E-95:
	   Compiler Design and Implementation - Spring 2015

		    Due: Midnight on April 5, 2015

1. (100 Points) Based on all the work you have completed so far, your
lexer from Problem Set 1, your YACC or Bison parser from Problem Set
2, and your symbol table management system from Problem Set 3, develop
code to perform semantic analysis.  That is, your code should walk
over the parse tree and perform type checking of the entire program by
refering to the symbol table.

After the entire parse tree and symbol table has been created as per
Problem Set 3, your program will perform type checking of every
expression in the program being compiled.  All appropriate conversions
need to be applied (usual casting conversions, usual assignment
conversions, usual unary conversions, usual binary conversions, etc.).
The type checking should include validity of references to identifiers
such as appropriateness of expressions used as lvalues, compatibility
for all operators, compatibility of actual function arguments to
formal function parameters, propagation of function return type to
utilization of the function's return value in an expression.  Remember
to appropriately check for no arguments and no return values for
functions.  Any errors you detect should be flagged with emitted error
messages.  These include parameter mismatches, return type mismatches.
If the types of components of expressions are not *identical*, your
compiler should add appropriate nodes into the parse tree to
explicitly perform type conversions.  These might include conversion
from char to short, short to int, int to long, signed to unsigned,
etc.  If the conversions do not result in an expression with valid
types, an error must be emitted.  You should update your pretty
printer to dump the additional explicit type conversion nodes in the
parse tree.

As always, the solution that you turn in should include a
demonstration that your program works and has been tested.  Thus, the
test programs you use as input and the output that your compiler
produces should be included with your other files.  Continue to use
"git" to turn in your completed work.