Answers to January 2002 CS2121 Exam Q2

(Parts in italics are just my working out loud, that I wouldn't expect to see in real exam answers.)

a)

float d; d = a + b + 2; ->
(float) (id,d) (;) (id,d) (=) (id,a) (+) (id,b) (+) (number,2) (;)
e.g. float is syntactically a keyword, ";" is punctuation and "=" and "+" are different operators, whereas a, b and d are all syntactically identifiers - the semantic information says which identifier.

b)

I would expect something better drawn than this, but otherwise similar:

	function----------
	/  |   \          \
    void   f   param       declaration
               /   \       |    |      \
              int  a	   |	float	d
			   |
			   statement
			   |	    \
			   |	     =
			   |	    / \
			   |       d   +
			   |	      / \
			   |	     +   2
			   |        / \
			   |       a   b
			   |
			   statement
				   \
				    =
				   / \
				  c   *
				     / \
				    d   3

c)

i)

float -> built-in type
f -----> function void params
		       |
		       v
a -----> param int local 1 ------> var float global 1
b -----> var float global 2
c -----> var float global 3
d -----> var int local 1
int ---> built-in type

As exit f, lose information about d and (current) a, resetting a back to previous definition, but don't lose parameter information for f e.g.:

float -> built-in type
f -----> function void params
		       |
		       v
	param int local 1
a -----> var float global 1
b -----> var float global 2
c -----> var float global 3
d
int ---> built-in type

ii)

should be links from each identifier to property entry in dictionary, giving kind (var/param etc.) and type (int=I/float=F etc.), which is then propagated around the tree and used for automatic conversions, type checking etc.

	function----------
	/  |   \          \
    void   f   param       declaration
               /   \       |    |      \
              int  a	   |	float	d
			   |
			   statement
			   |	    \
			   |	     =(F)
			   |	    / \
			   |      d(F) +(F)
			   |	      / \
			   |	    +(F) 2.0(F)
			   |         / \
			   |       I->F \
			   |        |    \
			   |      a(I)  b(F)
			   |
			   statement
				   \
				    =(F)
				   / \
				 c(F) *(F)
				     / \
				   d(F) 3.0(F)

I would also expect some explanation like e.g. handout 8

d)

i)

Bookwork from handout 9 and maybe also from handout 10

ii)

Bookwork from handout 10