Multiple Changes to CIVL Code

Model Changes

• introduce !LHSExpression, a subtype of !Expression
• rename ArrayIndexExpression to SubscriptExpression
• modify ModelBuilder to get rid of arrow expressions, replacing them with dot of star
• modify ModelBuilder to get rid of C's pointer-array pun:
  • in any subscript expression a[i], make sure a has array type. If it doesn't, translate to *(a+i)
  • in any place where a pointer is called for, but instead an array a is used, replace a with &a[0]. Examples include pointer arithmetic (a+i, a-b), argument to dereference operator *, actual arguments in function calls where the corresponding parameter has pointer type.
  • make sure the parameter type of a function call is never an array type. ABC should already be doing this.
• use an enumerated type like ExpressionKind for the different kinds of expressions, so switch statements can be used
• add a method to expressions like SymbolicExpression getConstantValue() and a corresponding setter, to cache the value of any expression that has a constant value, such as a literal expression

Semantics Changes

• use interfaces for !Executor, !Evaluator, etc.
• finish javadocs for all methods
• don't use !Vector. Use LinkedList if you only need to iterate; use ArrayList if you need constant time access
• !processType, etc: for these and other fields, make them canonic using !universe.canonic(…)!. This can improve efficiency.
• never return !null if a case is not handled. Instead throw an appropriate exception
• use !switch instead of big if...else if… sequence
• evaluation of dot expression should be simply return universe.tupleRead(evaluate(expr.struct()…), expr.index()) or something like that
• evaluation of SubscriptExpression should be simply return universe.arrayRead(evaluate(expr.array()…), evaluate(expr.index()…)) or something like that
• evaluate of NOT_EQUAL: use universe.neq()
• implement pointer addition and subtraction.
• implement string literals using universe.stringExpression() (it returns an array of char).
• references: re-do to use new (upcoming) methods in symbolic universe to create a reference to a point within a symbolic expression. this will eliminate the need to deal with navigation sequences. You still need to figure out the variable, scope and model IDs.
• use a tuple with one integer field for scope IDs instead of symbolic constants.
• don't do any string manipulation or parsing dynamically, if possible
• evaluate(…VariableExpression): the error reporting code for incorporating the state into the log entry seems general enough that you could factor it out into a separate method somewhere to re-use every time there is an error to report (maybe in Log?)
• construct and set the heap type in the constructor for !Evaluator, just like the other special types