Compiler HWK#4 Due date: 2:20pm, May 19, 2005

Write a simple compiler-interpreter for a simple PASCAL-like
expression language.

A sample program is as follows:

       PROGRAM program_name
       VAR %% beginning of variable declarations, required even no var's
          x, y, z: INTEGER;
       BEGIN
          READ(y);
          x := (y + 3 * 4) - 5;
          WRITE(y);
          WRITESP();
          WRITE(x);
          WRITELN();
       END

The definition of your language is as follows:
1. This language is case-sensitive with resevered words.
2. assignment is ":=", the statement terminator is ";"
   each line has at most one statement
3. variable must be declared before its usage.
   variable/program names uses the one in HWK1.
   can have only the type of integer (4-byte signed)
4. can have only three different statements
   a. assignment of expressions, where expressions
      can have variables, integer-constant, (, ), +, -, *, / and "uminus".
   b. input statement
         READ(single variable)
   c. output statements
         WRITE(single variable) ---  output a variable
         WRITESP()              ---  output a single space
         WRITELN()              ---  write a new line
   There is no space before and in between "()".
5. Anything after %% are comments until to the end of the line.
   Watch out for white spaces as in HWK 1.
6. Must detect the following error and reports its line number:
    a. invalid ID names
    b. undeclared variables
    c. illegal syntax
    d. duplicatedly declared variables
7. Must run the program if there is no error.

Hints: (1) Assume <= 256 variables can be declared.
           Each variable name has at most 32 characters.
           First allocate 256*4 bytes and keep track of
           the address of each variable.
       (2) The semantics of a variable name are different
           on the LHS and RHS of an assignment.
              LHS: retrieve the storage address of a variable and store
                   a value from the RHS to it
              RHS: retrieve the value of the variable


Note:     (1) To submit your homework, send an email to comp05@csie.ntu.edu.tw
          subject: HWK4: your student number and name
                   eg: "HWK4 - B91922xxx ¤ý¤p©ú"
          attachments: one file: B91922xxx.tar.gz
                       files must contain in the current dir
                       after uncompression and untar
          (2) You need to have LAX and YACC programs.

This homework MUST execute on Linux or FreeBSD workstations in our department.
Submitting files include a lex file, a Makefile, and optional C codes. The
Makefile MUST supports "make clean" and "make all" for cleaning,
and building the homework. An example of the Makefile can be
obtained from the course web. Do not use the samples without proper
changes.
The name of your executable after "make all" must be "hw4" and takes
input from standard input and writes to standard output.
Note that your program code is in the file
"program.p".
LEX takes input from program.p.
Your keyboard input becomes the standard input of your program.