scanner.yy

%{
  #include <stdio.h>
%}

%option noyywrap

IDENTIFIER  [a-zA-ZS+=][a-zA-Z0-9+=]*
DIGIT       [0-9]
LPAREN      \(
RPAREN      \)
QUOTE       [`']
DOT         \.
LBRACKET   \[
RBRACKET   \]

%%
{IDENTIFIER} {
  printf("An identifier: %s\n", yytext);
}

-?{DIGIT}+\.{DIGIT}+ {
  printf("A float: %s\n", yytext);
}

-?{DIGIT}+ {
  printf("An integer: %s\n", yytext);
}

{LPAREN} {
  printf("LPAREN: %s\n", yytext);
}

{RPAREN} {
  printf("RPAREN: %s\n", yytext);
}

{QUOTE} {
  printf("A quote %s\n", yytext);
}

{DOT} {
  printf("A Dot: %s\n", yytext);
}

{LBRACKET} {
  printf("LBRACKET: %s\n", yytext);
}

{RBRACKET} {
  printf("RBRACKET: %s\n", yytext);
}

%%

int main(int argc, char** argv) {
  yylex();
}

Run with
flex scanner.yy && cc lex.yy.c && ./a.out