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GO Classes DPP | COMPILER|LEXICAL ANALYZER

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2 2 votes

Consider the following lexical specification for a scanner:

  1. $\mathrm{KEYWORD\_IF: \verb|if|}$
     
  2. $\mathrm{ID: [a-z][0-9]*}$
     
  3. $\mathrm{NUM: [0-9]+}$
     

The scanner follows the Longest Match rule. In case of a tie in length, the token defined first in the specification takes priority. How many tokens will be generated for the input string "$\verb|if20if|$"?

3 Answers

1 1 vote
Since $[a-z][0-9]^*$ allows only one letter followed by digits, $\texttt{if20}$ is not an $\texttt{ID}$.

Hence, $\texttt{if20if} \Rightarrow \texttt{if} \;|\; \texttt{20} \;|\; \texttt{if}$

So, the number of tokens generated is $\boxed{3}$.
• edited by
0 0 votes

Answer : 3 Tokens

                 if20if :                           KEYWORD_IF   ----->   if

                                                     while, ID -----> i

                   According to Longest Match Rule KEYWORD_IF generated as first token

 

                20if:                                NUM -----> 20 

                                       NUM generated as second token 

 

and for      if :                     KEYWORD_IF -----> if

                            Again,KEYWORD_IF generated as thrd token

Hence,  Total 3 tokens generated

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