Exercise 2.

The grammar below generates sequences of declarations of the form $\bf id$ $\bf :$ T.

P	$$\longmapsto$$	D
D	$$\longmapsto$$	D $$\bf ;$$ D
D	$$\longmapsto$$	$$\bf id$$ $$\bf :$$ T
T	$$\longmapsto$$	$$\bf integer$$
T	$$\longmapsto$$	$$\bf float$$
T	$$\longmapsto$$	$$\bf array$$ $$\bf [$$ $$\bf num$$ $$\bf ]$$ $$\bf of$$ T1
T	$$\longmapsto$$	$$\uparrow$$ T1

As usual id is the token for identifiers, integer denotes a type of integers, float denotes a type of floating point numbers and num is the token for integer values. Note that array, $\uparrow$, ; , :, [, ] and of are terminals too. Moreover,

• $\bf array$ $\bf [$ $\bf num$ $\bf ]$ $\bf of$ T denotes the type of arrays of length $\bf num$.val with elements of type T.type.
• $\uparrow$ T denotes the type of pointers to elements of type T.type.

You are asked to write a translation scheme which computes the memory address of every declared name and stores this information in the symbol table. To reach that goal you may associate the nonterminal T with a synthesized attribute T.width that indicates the number of memory units taken by objects of type T.

• For T  $\longmapsto$  $\bf integer$ and T  $\longmapsto$  $\bf float$ it is usual to have T.width = 4 and T.width = 8 respectively.
• For T  $\longmapsto$  $\bf array$ $\bf [$ $\bf num$ $\bf ]$ $\bf of$ T the formula for T.width is easy to guess.
• For T  $\longmapsto$   $\uparrow$ T₁ remember that a pointer is an integer.

As usual, the nonterminal T has a synthesized attribute T.type. You are not asked to give the semantic rules computing T.type (although this is easy). You may need a global variable offset which gives the current available memory address:

• Before the first declaration is made, offset should be initialized to 0.
• As each name $\bf id$.name is seen, that name is entered in the symbol table with offset equal to the current value and offset is incremented by the width of the type of $\bf id$.name.
• The procedure call enter( $\bf id$.name, T.type, offset) creates a symbol-table entry for $\bf id$.name, with type T.type and memory address offset.

Answer 2