First time here? Checkout the FAQ!
+1 vote
I came across few Compiler Design Doubts, Please provide your cent.

$Q_1 :$ Can lexical analyser detect some/any type of errors?

I think yes, because while scanning to identify tokens, it may be the cases that a string pattern doesn't match with any keyword (or) entry in symbol table and gives error. But a detailed explaination will be appreciated.

$Q_2:$ In which phase of compilation Scope Checking happens? I guess sematic analyser, but I have no valid explaination

$Q_3: \color{navy}{A \rightarrow Aa}$ (Left linear) $\color{navy}{A \rightarrow aA}$(Right Linear). What can be said about $\color{navy}{A \rightarrow aAb}$
asked in Compiler Design by Veteran (24.1k points)   | 180 views

Q3:$A\rightarrow aAb$ is also known as Linear grammar.

What do we say about $A \rightarrow aAb$? Whether it is considered as left (or) right linear. (or) none of these $2$.

none of these 2.

You can say,

Every left (or) right linear grammar are Linear grammar but converse is not true.

And, $A \rightarrow AbA$ and $A \rightarrow AA$ are both Right and Left linear ??

how ?
Because, derivation can go like $\Rightarrow$

$A \rightarrow AbA$

$\Rightarrow $$A \rightarrow (AbA)bA$ and so on.
No.given grammar is not even linear.Follow the definition of linear grammar.

Yes,(you are right) the definition of left and right linear says all nonterminals. But the above $2$ grammars are both left and right-recursive. right??

yes above grammar both left and right-recursive.

1 Answer

+3 votes

Can lexical analyser detect some type of errors?
Yes it is True. Lexical Analyser detect lex error.

Can lexical analyser detect any type of errors?
No, it cant detect syntax or semantic error.

In which phase of compilation Scope Checking happens?
Semantic Analyser. Generally type checking takes place when output is coming out. It is possible onl if there is no lex and no syntax error. (

A→Aa (Left linear),  A→aA (Right Linear).
 A→aAb it is CFG

answered by Veteran (45.3k points)  
I read in some pdf that semantic checking can also take place in two phase syntax analyser. Is it true?
Who detects following error : {} 0+0 else if enum a = 4[]+3[] + *1 - 4;
Members at the site
Top Users Feb 2017
  1. Arjun

    4672 Points

  2. Bikram

    4004 Points

  3. Habibkhan

    3738 Points

  4. Aboveallplayer

    2966 Points

  5. sriv_shubham

    2278 Points

  6. Smriti012

    2212 Points

  7. Arnabi

    1814 Points

  8. Debashish Deka

    1788 Points

  9. sh!va

    1444 Points

  10. mcjoshi

    1444 Points

Monthly Topper: Rs. 500 gift card

20,788 questions
25,938 answers
21,923 users