CSE 109    Progam 7     Due   9 PM Thursday 17 April 2008
     (Late collection dates: 9 PM Saturday 19 April, Sunday 20 April)

     Create a subclass of your class Parser, say FullParser, so that
     when you replace an instance of Parser with an instance of FullParser
     from p6 your program parses and generates code for programs satisfying
     the complete syntax for the YAPL++ language.  Thus, it should be able to
     handle lines of code like

         goto 60 if 2*x > 3+y*y
         write  two*(x-3-y-z)/20
         two<-5+3*y

     That is, your p7 should be able to handle full-blown arithmetic
     expressions.

     Your program should read the command line, require that the commnad
     line have exactly three arguments,  and then use the three
     files listed on the command line, the first for input, the second
     for storing the results of the parse, and the third for storing the
     code generated. The input file should consist of what purports to
     be an YAPL++ program.  The first output file should consist of
     the results of the parse, including a message that the YAPL++ program
     is correct, or a diagnosis of the first parse error.  If the parse
     succeeds, the second output file should have the corresponding SML
     code, including the text listed after "end" in the input file.

     To submit your assignment, create a subdirectory of /csc109.081 called
     p7 (that is, from your root directory csc109.081/p7) for doing your
     work.  Indicate you wish the assignment to be collected by touching
     the unix command "touch DONE", which will create a file of 0 bytes named
     DONE.  Then all files in the subdirectory p7 (but not in subdirectories
     of the subdirectory p7) will be collected. I will test your program
     using your Makefile, first executing the command 'make clean', and then
     executing the command 'make'. I will run your program with sample
     input files, some syntactically correct, some not.  I will use sml to
     run the code generated from syntactically correct programs.

     NOTE: IT IS VERY IMPORTANT THAT YOU IMPLEMENT THIS ASSIGNMENT WITH A
     SUBCLASS OF PARSER.

     Note: Except for .o files accessed from /proj/csc109/p6, all files you
     use should be in the p7 directory. IT IS IMPORTANT THAT YOU DO NOT
     have your makefile reference files from directories that you created
     for earlier assignments. Such files will not be collected. My attempt to
     "make" your code will fail, causing me some consternation.  You want to
     avoid that.

     Note: I have stored some YAPL++ files that I will use to test your
     programs in /proj/csc109/p7.

     Even though I am happy that I have detected no clear evidence of unfair
     collaboration this semester, I repeat still again, read the statement
     in the syllabus about what it means to unfairly collaborate.