L attributed grammer

Question

I know that every S attributed grammar is L attributed but not vice versa. Can anybody give example of the case if i print the semantic rules using L attributed the result will be different from the S attributed evaluation ? And how should i print the rules in both cases.

Explain both case in this example :

 

Consider the translation scheme shown below
$\mathrm{S} \rightarrow \mathrm{T} R$
$\mathrm{R} \rightarrow+\mathrm{T}$ \{print ('+'); $\} \mathrm{R} \mid \varepsilon$
$\mathrm{T} \rightarrow$ num \{print (num.val); $\}$
Here num is a token that represents an integer and num.val represents the corresponding integer value. For an input string ' $9+5+2$ ', this translation scheme will print
(Note: Use L-attributed evaluation to produce output)

• A. $9+5+2$
  
• B. $95+2+$
  
• C. $952++$
  
• D. ++952

Comments

L- attributed evaluation is like, on first time you are seeing it, evaluate its semantic rule.

S- attributed evaluation is like, on last time you are seeing it, evaluate its semantic rule.

but in this example, there is no L-attribute or S- attribute ===> just use Post order traversal or Depth first search from left to right ===> 9 5 + 2 +

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So brother are u saying that in L attributed the moment I hit the production execute its semantic rule and in S attributed when the reduction occurs then execute the rule?

Brother are u sure because I feel its the other way around (not sure though).

Can you please verify once :)

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L attributed means, it can take values from it's left side and parent ===> when you first time hit it, then you already completed it's parent and left side variable.

Answer 1

B is the ans

Comments

What is the difference between S attributed and L attributed evaluation ?. if a grammar is L attributed i can simply solve it and thats would also be the result if S attributed were perfomed. But if i grammar is S attributed then how its solved ?