1. Chapter 5. Syntax-Directed Translation

2. Fig. 5.2. Syntax-directed definition of a simple desk calculator
Production
Semantic Rules
L  E n
print ( E.val )
E  E1 + T
E.val := E1.val + T.val
E  T
E.val := T.val
T  T1 * F
T.val := T1.val + F.val
T  F
T.val := F.val
F  ( E )
F.val := E.val
F  digit
F.val := digit.lexval
Fig Syntax-directed definition of a simple desk calculator

3. Fig. 5.3. Annotated parse tree for 3*5+4n.

4. Fig. 5.4. Syntax-directed definition with inherited attribute L.in.
Production
Semantic Rules
D  T L
L.in := T.type
T  int
T.type := integer
T  real
T.type := real
L  L1 , id
L1.in := L.in
addtype ( id.entry , L.in )
L  id
Fig Syntax-directed definition with inherited attribute L.in.

5. Fig. 5.5. Parse tree with inherited attribute in at each node labeled L.

6. Fig. 5.6. E.val is synthesized from E1.val and E2.val

7. Fig. 5.7. Dependency graph for parse tree of Fig. 5.5

8. Fig. 5.16. Implementation of a desk calculator with an LR parser.
Production
Code Fragment
L  E n
print ( val [top] )
E  E1 + T
val [ntop] := val [top – 2]+val [top]
E  T
T  T1 * F
val [ntop] := val [top – 2]×val [top]
T  F
F  ( E )
val [ntop] := val [top – 1]
F  digit
Fig Implementation of a desk calculator with an LR parser.

9. L-Attributed Definitions
A syntax-directed definition is L-attribute if each inherited attribute of Xj,
1≤ j≤n, on the right side of A → X1X2 · · · Xn , depends only on
1. the attributes of the symbols X1 , X2 , · · · , Xj-1 to the left of Xj in the production and
the inherited attributes of A.
Note that every S-attributes definition is L-attributed, because the
restrictions (1) and (2) apply only to inherited attributes

10. Example 5.17. The type of an identifier can be passed by copy rules
using inherited attributes as shown in Fig (adapted from Fig. 5.7).
We shall first examine the moves made by a bottom-up parser on the input real p, q, r
then we show how the value of attirbute T.type can be accessed when the
productions for L are applied. The translation scheme we wish to implement is
D  T L { L.in := T.type } T  int { T.type := integer } T  real { T.type := real } L  { L1.in := L.in } L1 , id { addtype ( id.entry , L.in ) } L  id { addtype ( id.entry , L.in ) }

11. Fig.5.32. At each node for L, L.in = T.type.
If we ignore the actions in the above translation scheme, the sequence of
moves made by the parser on the input of Fig is as in Fig For
clarity, we show the corresponding grammar symbol instead of a stack
state and the actual identifier instead of the token id.

12. Input state Production Used real p,q,r − real T T → real ,q,r T p T L
L → id
q,r
T L , ,r
T L , q
L → L , id r
T L , r D
D → T L
Fig Whenever a right side for L is reduced, T is just below the right side.

13. Fig. 5.34. The value of T.type is used in place of L.in
Production
Code Fragment
D  T L ;
T  int
val [ntop] := integer
T  real
val [ntop] := real
L  L1 , id
addtype (val [top] , val [top−3] )
L  id
addtype (val [top] , val [top−1] )
Fig The value of T.type is used in place of L.in

14. S → aAC C.i := A.s S → bABC C → c C.s := g ( C.i )
Example As an instance where we cannot predict the position, consider the
following translation scheme:
(5.6)
C inherits the synthesized attribute A.s by a copy rule. Note that there may or
may not be a B between A and C in the stack. When reduction by C → c is
performed, the value of C.i is either in val [top−1]or in val [top−2], but it is
not clear which case applies.
Production
Semantic Rules
S → aAC
C.i := A.s
S → bABC
C → c
C.s := g ( C.i )

15. Fig. 5.35. Copying an attribute value through a marker M.
Production
Semantic Rules
S → aAC
C.i := A.s
S → bABMC
M.i := A.s ; C.i := M.s
C → c
C.s := g ( C.i )
M → є
M.s := M.i є
(a) original production
(b) modified dependencies
Fig Copying an attribute value through a marker M.