Section 3 with Remik (rz33@cornell.edu) 
Meeting #2 Notes
********************************************************
Administrivia:  Assignment #1 due next week
		Grading scale: to be determined
Review:		Grammar
		CS211In interface and class
		Writing a compiler with CS211In

Grammars for language specification
***********************************
We use BNF to specify the language.  BNF means Backus Naur Form, named
after John Backus and Peter Naur.  The 'language' resulted from
private communication over the ALGOL programming language in 1958. 
They found it difficult to express their own interpretations of ALGOL,
so they decided to create a general framework to describe a language.

Toy Language Example:
	Exp ::= (Exp Op Exp) | INT | Op "ctr"
	Op  ::= "+" | "++"
	INT ::= "0" | "-1" | "+1" ... 

All the symbols to the left of ::= are called categories, while
literals are enclosed by quotes.  The last item is a prefix
incrementer.  Basically it has the side effect of incrementing
the variable by 1 and returns the new value.

CS211In Interface
*****************
constants: INTEGER, WORD, OPERATOR

methods:
	int peekAtKind()
	int getInt()
	String getWord()
	bool check(char) 
	bool check(String)

Compiler writing with CS211In
*************************************************************
Here is a compiler for the language above (no error handling).

String getExp(CS211In f) {
	switch( f.peekAtKind() ) {
		case OPERATOR: {
			if (f.check("+")) {
				// check for prefix operator
			  if (f.check("+")) {
          // look ahead for our 1 variable ctr
            if (f.check("ctr")) {
              // increment, store and make avaible for assignment
              return "PUSHOFF 1\n PUSHIMM 1\n" +
                     "ADD\n STOREOFF 1\n PUSHOFF 1\n";
             } else {
              // otherwise it is just an expression
              String s1 = f.getExp(f);
              return s1 + "PUSHIMM 1\n ADD\n";
             }
        } else {
          // addition operator
           String s1 = f.getExp(f);
           return s1 + "ADD\n";
        }
      }
    case WORD: // handle variables
    ...
  }
}