/*
Commented By: Christopher Lopes
File Name: ycalc.cup
To Create: > java java_cup.Main < ycalc.cup
*/

/* ----------------------Preliminary Declarations Section--------------------*/

/* Import the class java_cup.runtime.* */
import java_cup.runtime.*;

/* Parser code so that it can interface with the scanner created with JFlex and change the way that it reports errors (include line and column number of the error).*/
parser code {:
Lexer lexer;

public parser(Lexer lexer) {
this.lexer = lexer;
}

/* Change the method report_error so it will display the line
and column of where the error occurred in the input as well as the reason
for the error which is passed into the method in the String 'message'. */
public void report_error(String message, Object info) {

/* Create a StringBuffer called 'm' with the string 'Error' in it. */
StringBuffer m = new StringBuffer("Error");

    /* Check if the information passed to the method is the same type as the
       type java_cup.runtime.Symbol. */
    if (info instanceof java_cup.runtime.Symbol) {

      /* Declare a java_cup.runtime.Symbol object 's' with the information in the
          object info that is being typecasted as a java_cup.runtime.Symbol object. */
      java_cup.runtime.Symbol s = ((java_cup.runtime.Symbol) info);

/* Check if the line number in the input is greater or equal to zero. */
if (s.left >= 0) {

        /* Add to the end of the StringBuffer error message the line number of
           the error in the input. */
        m.append(" in line "+(s.left+1));

        /* Check if the column number in the input is greater or equal to
           zero. */
        if (s.right >= 0)

          /* Add to the end of the StringBuffer error message the column number
             of the error in the input. */
          m.append(", column "+(s.right+1));
        }
    }

    /* Add to the end of the StringBuffer error message created in this
       method the message that was passed into this method. */
    m.append(" : "+message);

    /* Print the contents of the StringBuffer 'm', which contains an error
       message out on a line. */
    System.err.println(m);
}

/* Change the method report_fatal_error so when it reports a fatal error it
     will display the line and column number of where the fatal error
     occurred in the input as well as the reason for the fatal error which is
     passed into the method in the object 'message' and then exit.*/
public void report_fatal_error(String message, Object info) {
    report_error(message, info);
    System.exit(1);
    }
:};

/* Return to Using CUP */

/* Use the scanner created with JFlex */
scan with {: return lexer.yylex(); :};

/* ------------Declaration of Terminals and Non Terminals Section----------- */

/* Terminals (tokens returned by the scanner).

   Terminals that have no value are listed first and then terminals that do
   have an value, in this case an integer value, are listed on the next line
   down. */
terminal           SEMI, PLUS, MINUS, TIMES, DIVIDE, LPAREN, RPAREN;
terminal Integer   NUMBER, ID;

/* Non Terminals used in the Grammar Section.

   Non Terminals that have an object value are listed first and then Non Terminals
   that have an integer value are listed. An object value means that it can be
   any type, it isn't set to a specific type. So it could be an integer or a String or
   whatever. */
non terminal Object     expr_list, expr_part;
non terminal Integer    expr, factor, term;

/* -------------Precedence and Associatively of Terminals Section----------- */

/*
Precedence of Non Terminals could be defined here. If you do define precedence
here you won't need to worry about precedence in the Grammar Section.
i.e. that TIMES should have a higher precedence than PLUS.

The precedence defined here would look something like this where the lower
line always will have higher precedence than the line before it.

precedence left PLUS, MINUS;
precedence left TIMES, DIVIDE;
*/

/* ----------------------------Grammar Section-------------------- */

/* The grammar for our parser.

Return to Using CUP

/* 'expr_list' is the start of our grammar. It can lead to another 'expr_list'
followed by an 'expr_part' or it can just lead an 'expr_part'. The lhs of
the Non Terminals 'expr_list' and 'expr_part' that are in the rhs side of the
production below need to be found. Then the rhs sides of those Non Terminals
need to be followed in a similar manner, i.e. if there are any Non Terminals
in the rhs of those productions then the productions with those Non Terminals
need to be found and those rhs's followed. This process keeps continuing
until only Terminals are found in the rhs of a production. Then we can work
are way back up the grammar bringing any values that might have been assigned
from a Terminal. */

expr_list ::= expr_list expr_part
|
expr_part;

/* 'expr_part' is an 'expr' followed by the terminal 'SEMI'. The ':e'
after the Non Terminal 'expr' is a label an is used to access the value of
'expr' which will be an integer. The action for the production lies between
{: and :}. This action will print out the line " = + e" where e is the value of
'expr'. Before the action takes places we need to go deeper into the grammar
since 'expr' is a Non Terminal. Whenever a Non Terminal is encountered on
the rhs of a production we need to find the rhs of that Non Terminal until
there are no more Non Terminals in the rhs. So when we finish going through
the grammar and don't encounter any more Non Terminals in the rhs productions
will return until we get back to 'expr' and at that point 'expr' will contain
an integer value. */

expr_part ::= expr:e
              {: System.out.println(" = " + e); :}
              SEMI
              ;

/* 'expr' can lead to 'factor PLUS expr', 'factor MINUS expr', or 'factor'.
The 'TIMES' and 'DIVIDE' productions are not at this level. They are at a
lower level in the grammar which in affect makes them have higher precedence.
Actions for the rhs of the Non Terminal 'expr' return a value to 'expr'. This
value that is created is an integer and gets stored in 'RESULT' in the action.
RESULT is the label that is assigned automatically to the rhs, in this case 'expr'.
If the rhs is just 'factor' then 'f' refers to the Non Terminal 'factor'.
The value of 'f' is retrieved with the function 'intValue()' and will be
stored in 'RESULT'. In the other two cases 'f' and 'e' refers to the Non
Terminals 'factor' and 'expr' respectively with a Terminal between them,
either 'PLUS' or 'MINUS'. The value of each is retrieved with the same
function 'intValue'. The values will be added or subtracted and then the new
integer will be stored in 'RESULT'.*/

expr      ::= factor:f PLUS expr:e
              {: RESULT = new Integer(f.intValue() + e.intValue()); :}
              |
              factor:f MINUS expr:e
              {: RESULT = new Integer(f.intValue() - e.intValue()); :}
              |
              factor:f
              {: RESULT = new Integer(f.intValue()); :}
              ;

/* 'factor' can lead to 'factor TIMES term', 'factor DIVIDE term', or
'term'. Since the productions for TIMES and DIVIDE are lower in the
grammar than 'PLUS' and 'MINUS' they will have higher precedence. The same
sort of actions take place in the rhs of 'factor' as in 'expr'. The only
difference is the operations that takes place on the values retrieved with
'intValue()', 'TIMES' and 'DIVIDE' here instead of 'PLUS' and 'MINUS'. */

factor    ::= factor:f TIMES term:t
              {: RESULT = new Integer(f.intValue() * t.intValue()); :}
              |
              factor:f DIVIDE term:t
              {: RESULT = new Integer(f.intValue() / t.intValue()); :}
              |
              term:t
              {: RESULT = new Integer(t.intValue()); :}
              ;

/* 'term' can lead to 'LPAREN expr RPAREN', 'NUMBER', or 'ID'. The first
production has the Non Terminal 'expr' in it so the production with its lhs
side needs to be found and followed. The next rhs has no Non Terminals. So
the grammar ends here and can go back up. When it goes back up it will bring
the value that was retrieved when the scanner encounter the token 'NUMBER'.
'RESULT' is assigned 'n', which refers to 'NUMBER', as the action for this
production. The same action occurs for 'ID', except the 'i' is used to refer
to 'ID'. 'ID' is also the only thing on the rhs of the production. And since
'ID' is a Terminal the grammar will end here and go back up. */

primary   ::= LPAREN expr:e RPAREN
              {: RESULT = e; :}
              |
              NUMBER:n
              {: RESULT = n; :}
              |
              ID:i
              {: RESULT = i; :}
              ;

/* Return to Using CUP */