A cryptographic calculator performs simple operations on strings of a kind that are used in

classical cryptosystems. It is also able to combine these operations in a natural way.

Suppose x = x 1 x 2 x n and k = k 1 k 2 k t are two strings, where x i and k i denote the i-th

letters of x and k respectively.

QUESTION: Using the following code as a starting point construct a lex file, called crypt.l and use it

to build a lexical analyser for CRYPT.

/S E

S

E E + E

E E E

E SIMPLESUB(E, STRING)

E VIGENERE(E, STRING)

E LOCTRAN(E, DIGITS)

E STRING

/*** Definition section ***/

%{

/* C code to be copied verbatim */

#include

#include

void yyerror(char *);

#include "y.tab.h";

%}

%%

/*** Rules section ***/

/* yytext is a string containing the matched text. */

/* Strings are all lower case*/

[a-z]+{

printf("Token: STRING;Lexeme: %s ", yytext);

yylval.str = strdup(yytext);

returnSTRING;

}

Reverse{

printf("Token: REVERSE;Lexeme: %s ", yytext);

yylval.str = strdup(yytext);

returnREVERSE;

}

[#()]{

printf("Token and Lexeme: %s ", yytext);

return*yytext;

}

{

printf("Token and Lexeme: ");

return*yytext;

}

[ \t]{}/*skip whitespace*/

.{

printf("Invalid character. ");

/*

yyerror("invalid character");

*/

}

/*will match any single character that does not match

any of the above patterns

*/

%%

/*** C Code section ***/

void yyerror(char *s) {

fprintf(stderr, "line %d: yytext = %s.Error msg: %s. ", yylineno, yytext, s);

}

int yywrap(void) {

return 1;

}

/*comment out the functionmain()if usinglexwithyacc

int main(void) {

yylex();

return 0;

}

*/

some sample ouput is:

$ ./a.out

Loc(Sim(Vig(therewasmovementatthestation,banjo),thequickbrownfxjmpsvlazydg),10)

Token: LOCTRAN; Lexeme: Loc

Token and Lexeme: (

Token: SIMPLESUB; Lexeme: Sim

Token and Lexeme: (

Token: VIGENERE; Lexeme: Vig

Token and Lexeme: (

Token: STRING; Lexeme: therewasmovementatthestation

Token and Lexeme: ,

Token: STRING; Lexeme: banjo

7Token and Lexeme: )

Token and Lexeme: ,

Token: STRING; Lexeme: thequickbrownfxjmpsvlazydg

Token and Lexeme: )

Token and Lexeme: ,

Token: DIGITS; Lexeme: 10

Token and Lexeme: )

Token and Lexeme:

Control-D

$ ./a.out

V(twentysix - eleven, eleven)

Token: VIGENERE; Lexeme: V

Token and Lexeme: (

Token: STRING; Lexeme: twentysix

Token and Lexeme: -

Token: STRING; Lexeme: eleven

Token and Lexeme: ,

Token: STRING; Lexeme: eleven

Token and Lexeme: )

Token and Lexeme: