P – 4; Q – 1; R – 3; S – 2

P – 2; Q – 3; R – 1; S – 4

P – 2; Q – 1; R – 3; S – 4

P – 4; Q – 3; R – 2; S – 1

An attribute grammar is a syntax-directed definition (SDD) in which the functions in the semantic rules have no side effects

The attributes in a L-attributed definition cannot always be evaluated in a depth-first order

Synthesized attributes can be evaluated by a bottom-up parser as the input is parsed

All L-attributed definitions based on LR(1) grammar can be evaluated using a bottom-up parsing strategy

(1) $ S \rightarrow AaAb $, (2) $ S \rightarrow BbBa $, (3) $ A \rightarrow \epsilon $, (4) $ B \rightarrow \epsilon $

(1) $ S \rightarrow BbBa $, (2) $ S \rightarrow AaAb $, (3) $ A \rightarrow \epsilon $, (4) $ B \rightarrow \epsilon $

(1) $ S \rightarrow AaAb $, (2) $ S \rightarrow BbBa $, (3) blank, (4) blank

(1) $ S \rightarrow BbBa $, (2) $ S \rightarrow AaAb $, (3) blank, (4) blank

(1) = [] s i     (3) * (0) (2)     (6) []= x i

(1) []= s i     (3) - (0) (2)     (6) =[] x (5)

(1) =[] s i     (3) * (0) (2)     (6) []= x (5)

(1) []= s i     (3) - (0) (2)     (6) =[] x i