Compiler HWK#5 Due date: 2:20pm, June 13, 2013

Write a simple compiler to parse
a simple PASCAL-like expression language with 
integer and real data types, block structure,
1-D array, I/O statement, and IF .. THEN .. ELSE.
Code generation in C-- (Version 2.3);

A sample program is as follows:

       PROGRAM program_name
          VAR %% beginning of variable declarations, optional
          INTEGER: x, y, z;
          REAL: a;
          ARRAY[-20..30] OF REAL: b; %% a total of 61 elements
          ENDVAR
       BEGIN
          READ(y);
          x := (y + 3 * 4) - 5;
          IF (x >= -20) AND (x <= 30)
          THEN  BEGIN
                  a := 0.3;
                  b[x] := a;
                END
          ENDIF
          WRITE(y);
          WRITESP();
          WRITE(x);
          WRITELN() ;
       END

The definition of your language is as follows:

1. This language is case-sensitive with reserved words.

    1.1 <main program def>
        PROGRAM name
         optional var decl
        BEGIN
         statements or blocks
        END
    1.2 <optional var decl> is epsilon or
        VAR
        ...
        ENDVAR

        VAR ... ENDVAR is a declaration of local variables which can be
        empty or completely missing.
        VAR ... ENDVAR must be before any statements and can have only
        one appearance.

    1.3  IF boolean-expression
         THEN block/statement
         ENDIF

         IF boolean-expression
         THEN block/statement
         ELSE block/statement
         ENDIF

    1.4 <block>
        BEGIN
	   statements or blocks
        END

        BEGIN and END starts and ends a block, respectively.

    1.5 boolean-expression:
         
           expression (> | < | = | <= | >= | <>) expression
           boolean-expression (OR | AND) boolean-expression
           NOT boolean-expression
        Precedence and Associativity for operators follow C.

    1.6 <statements>
       a. assignment of expressions, where expressions
          can have variables, real-constant (digits.digits),
          integer-constant (digits), (, ), +, -, *, / and "uminus".
          assignment is ":=",
       b. input statement %% it's legal when sysio.h is included
          READ(single variable)
       c. output statements %% it's legal when sysio.h is included
          WRITE(single variable) ---  output a variable
          WRITESP()              ---  output a single space
          WRITELN()              ---  write a new line
          There may have spaces before, in between or after "()".
       d. The statement terminator is ";"

2. each line has at most one statement
   can have a blank line
   cannot have a null statement, ";"
3. Two different data types: INTEGER and REAL.
   3.0 There is no auto-type conversion.
   3.1 Each occupies 4 bytes.
   3.2 No type conversion is allowed.
   3.3 Can have 1-D array of INTEGER or REAL
          ARRAY[20..30] OF INTEGER: x,y,z;
          ...
          x[a] := y[3] + 20;

4. variable must be declared before its usage.
   variable/program names uses the rule as HWK4.
   However, the length of a variable name is 1024. There can have lots
   of variables. I expect you to use either hash table or
   balanced-binary search tree for symbol tables.
5. Anything after %% are comments until to the end of the line.
6. Must detect at least
   the following error and reports its line number(report all errors):
    a. invalid ID names
    b. undeclared variables
    c. duplicatedly declared variables
    d. mismatched data type
    e. invalid constant
    f. illegal syntax

7. Name your compiler "pascal-" and it should support -S and -o option:

    pascal- program.p -o prog %% generate an executable called prog and default is p.out
    pascal- -S program.p         %% generate an file contains the intermediate code in C-- 

Note:
     (1) TA will announce details for error handling later.
     (2) To submit your homework, use the software submission system 
           designed by TA. Read TA's web site for details.
     (3) You need to have LEX and YACC programs.
     (4) TA will announce rules for submitting homeworks.