Sample questions to study for exam 2:

1. (20 points)

Draw the abstract syntax trees that a Macro compiler would build to
represent each of the following statements. 

(a) A := B + 5
(b) A, B, C : Integer
(c) if X>2.5 then read(Y) else Y:=10.0 end if 

2. (30 points)
Suppose you are compiling a language that includes a IF-LOOP-UNTIL 
statement, which has the form:

IF boolean-expression-1 LOOP
	statement _list
UNTIL boolean-expression-2

The semantics of this statement are what would be ; next expected from the
keywords: if boolean-expression-1 evaluates to True, repeatedly perform
statement-list until boolean-expression-2 evaluates to True at the end of
an execution of the statement list.

(a) Write a production for adding this kind of statement to the Macro grammar.
(b) Draw the abstract syntax tree structure that would be used to represent
such a statement. 
(c) In pseudo-code (or C, if you wish), define the code generation 
operation for the tree node that represents the IF-LOOP-UNTIL statement.

3. (25 points)
(a) Describe the implementation of the standard search rule for
interpreting identifiers in a language that allows arbitrarily nested 
scopes, presuming that each scope is represented by its own symbol table.

(b) In Modula-3, a set of declarations can be grouped together and named as
an Interface. A Module may be defined to export a single interface (like a
Macro package) or it may export multiple interfaces. (Interface definitions
are syntactically separate from module definitions.) Within a module, the
names declared in all of its exported interfaces are accessible just as if
they were directly declared in the module itself. Explain how you would
implement identifier look up from within a module body given the above
rules.

4. (25 points)
Consider the following procedure declarations, where nesting is indicated
 by indentation:

procedure A
	procedure B
		procedure C
	procedure D
		procedure E

After the following sequence of procedure calls:

Main -> A -> D -> E -> E -> B -> C -> B -> D -> E

(a) Show the state of the run-time stack and display during the execution
of the final call to E. Include some indication of the value of the saved
display register contained in each procedure activation record.

(b) Show the static chain pointer that would be included in each activation
record if a static chain were being used instead of a display.