Commented By: Christopher Lopes
File Name: lcalc.flex
To Create: > jflex lcalc.flex
                and then after the parser is created
                  > javac Lexer.java

/* --------------------------Usercode Section------------------------ */

/* import these classes:
        sym                     --class we create with CUP
import java_cup.runtime.*;
import sym;


/* -----------------Options and Declarations Section----------------- */

/* The name of the class JFlex will create will be Lexer.
   Will write the code to the file Lexer.java.
%class Lexer

The current line number can be accessed with the variable yyline
and the current column number with the variable yycolumn.

/* Will switch to a CUP compatibility mode to interface with a CUP
generated parser.


Code between %{ and %}, both of which must be at the beginning of a line, will
be copied letter to letter into the lexer class source.  Here you declare
member variables and functions that are used inside scanner actions.

  /* To create a new java_cup.runtime.Symbol with information about the current
     token, the token will have no value in this case. */
  private Symbol symbol(int type) {
    return new Symbol(type, yyline, yycolumn);

  /* Also creates a new java_cup.runtime.Symbol with information about the
     current token, but this object has a value. */
  private Symbol symbol(int type, Object value) {
    return new Symbol(type, yyline, yycolumn, value);


/*  Return to Using JFlex  */

Macro Declarations

These declarations are regular expressions that will be used latter in the
Lexical Rules Section.

/* A line terminator is a \r (carriage return), \n (line feed), or \r\n. */
LineTerminator = \r|\n|\r\n

/* White space is a line terminator, space, tab, or line feed. */
WhiteSpace     = {LineTerminator} | [ \t\f]

/* A literal integer is is a number beginning with a number between one and nine
followed by zero or more numbers between zero and nine or just a zero. */
dec_int_lit = 0 | [1-9][0-9]*

/* A identifier integer is a word beginning a letter between A and Z, a and z,
or an underscore followed by zero or more letters between A and Z, a and z,
zero and nine, or an underscore. */
dec_int_id = [A-Za-z_][A-Za-z_0-9]*

/*  Return to Using JFlex  */


/* ------------------------Lexical Rules Section---------------------- */

This section contains regular expressions and actions, i.e. Java code, that
will be executed when the scanner matches the associated regular expression. */

/* YYINITIAL is the state at which the lexer begins scanning.  So these regular
expressions will only be matched if the scanner is in the start state


/* Return the token SEMI declared in the class sym that was found. */
";"                     { return symbol(sym.SEMI); }

/* Print the token found that was declared in the class sym and then return it.*/
"+"                     { System.out.print(" + "); return symbol(sym.PLUS); }
"-"                     { System.out.print(" - "); return symbol(sym.MINUS); }
"*"                     { System.out.print(" * "); return symbol(sym.TIMES); }
"/"                     { System.out.print(" / "); return symbol(sym.DIVIDE); }
"("                     { System.out.print(" ( "); return symbol(sym.LPAREN); }
")"                     { System.out.print(" ) "); return symbol(sym.RPAREN); }

/* If an integer is found print it out, return the token NUMBER that represents
an integer and the value of the integer that is held in the string yytext
which will get turned into an integer before returning */
{dec_int_lit}           { System.out.print(yytext());
                          return symbol(sym.NUMBER, new Integer(yytext())); }

/* If an identifier is found print it out , return the token ID that
represents an identifier and the default value one that is given to all
identifiers. */
{dec_int_id}            { System.out.print(yytext());
                          return symbol(sym.ID, new Integer(1));}

/* Don't do anything if whitespace is found */
{WhiteSpace}            { /* just skip what was found, do nothing */ }


/* No token was found for the input so through an error.  Print out an
'Illegal character' message with the illegal character that was found.*/
.                                   { throw new Error("Illegal character <"+yytext()+">");}

/*  Return to Using JFlex  */