CSC362 2004S, Class 30: A Pascal Parser

Admin:
* Parser nearly ready.  Released at 4:15 p.m.  Extra credit for finding errors.
* Today: Some review of parsing (since it's on my mind)
* Wednesday: Learn about target code.
* Cool talk Friday at noon.  Free pizza.

Overview:
* Your problems in parsing.
* My problems in parsing.
* Solving those problems.
* On type checking.

Common problems
* Structural
  * Compiling Java: You have to learn it some time.
  * Sam's design of Node.java sucks: 
  * No standard grammar to use
  * Dealing with separating the problem into parts
    * Joining parts
    * Tracking down errors
  * Scale
  * Figuring out where errors occur
  * Biting off more than you can chew
* Grammar
  * Variables and Expressions
    * Procedure call vs. assignment statement
      * Sam's hack: Simulate lookahead by passing identifier
      * Better strategy: Permit more lookahead
  * Differentiating related things

Splitting up work in the type checker:
* Create a new class with a simple check() method.  The default behavior is to recursively check all the children.
* For certain kinds of nonterminals, we need to override that method
* Keep a hash table of nonterminal/overridden methods
* The "overriden methods" can be built in separate classes
   checker.add(PascalNonterminals.WHILELOOP, Paul.whileChecker);
   checker.add(PascalNonterminals.EXPRESSON, Dimitar.expressionChecker);