===============================
2nd Midterm and PA3 Post Mortem
===============================

--------------------------------------------------------
Logistics

    If want to ask for any regrades then leave midterm with me.

    HW8 is due Monday.

    PA4 is due a week from Monday.

    Friday's recitation will be 1.5 hour HW8 and PA4 help session 
    from 10-11:30.

--------------------------------------------------------
Question 1 from Midterm 

    Creating LL(1) expression grammars.
    
    
    Starting point (ambiguous expression grammar):
        E -> E + E | E = E | E - E | E * E | -E | (E) | NUM
    
    
    Steps to follow
    
    (1) Look up the precedence levels and order them from lowest
        to highest precedence.
    
    
    
    
    (2) Create a non-terminal in the grammar for each precedence level.
        Each precedence level should include a production for each operator
        at that level and a production that goes directly to the next
        higher-level of precedence.
            E1 -> ...    | E2
            E2 -> ...    | E3
            ...
        
        
    (3) The productions with operators need to be self recursive and if 
        they are binary operators should also
        reference the next highest level of precedence.
        
            E1 -> E2 = E1               | E2
            E2 -> E2 + E3 | E2 - E3     | E3
            ...
    
    
    
    
    
    (4) Then the grammar needs converted to LL(1) through the use
        of left factoring and the removal of left recursion. 
    
            ==> show that removing left recursion can be done in two ways
            

    
    

Reference information:
    Eliminating ambiguity in expression grammars.  Reading that was posted
    for October 4th.
    http://itu.dk/~mogel/SPLC2011/lectures/eliminatingAmbiguity.pdf

    Good text notes about this that take the approach of changing the
    left recursion into right recursion and the left factoring.
    https://www.cs.rochester.edu/~brown/173/readings/05_grammars.txt


--------------------------------------------------------
Question 4 from Midterm

    Why don't we need to pass down the left AST for a right associative
    operator?
    
        We don't for unary right associative operators.
        
        However, we actually do for binary right associative operators?
        


--------------------------------------------------------
Question 5 from Midterm

    Nullable, FIRST, FOLLOW, and Predictive parse table for the following:
    
        (1) prog       -> stmtlist EOF
        (2) stmtlist   -> stmtlist stmt
        (3)            |  epsilon
        (4) stmt       -> EAT NUM mallow
        (5)            |  SAVE NUM mallow
        (6) mallow     -> PINK STARS
        (7)            |  BLUE DIAMONDS



------------------------
mstrout@cs.arizona.edu, 11/1/16