COSC 3410
Assignment #4
Due: Friday, Oct 15

-ROUGH DRAFT-

You can work in teams of two or by yourself.

Extend the expanded (*,/) WAE language to include a conditional expression:

 (if< expr1 expr2 val1 val2)
 
which has the value val1 if (expr1 < expr2) and val2 otherwise.
So, {with {a 5} {if< a 10 77 99}} would have the value 77.

Add a unary minus [ new tree (minus (operand number?)) ]
  {with {x -12} {- x}} has value 12

So, new grammar is:

<CWAE> ::= <num>
         | <id>
         | {+ <CWAE> <CWAE>}
         | {- <CWAE> <CWAE>}
         | {* <CWAE> <CWAE>}
         | {/ <CWAE> <CWAE>}
         | {- <CWAE>}
         | {with {<id> <CWAE>} <CWAE>}
         | {if< <CWAE> <CWAE> <CWAE> <CWAE>}
         
Write an interpreter for this language.
Implement error checking for these new expressions (and with).

A sample program:


{with {x 9}    ; you can change these vals, but the larger one should
  {with {y 3}  ; always wind up at the left of the final number
               ; and the smaller one at the right
     {with  {min  {if< x y
                     x 
                     y}}
        {with  {max  {if< x y 
                        y 
                        x}}
           {+ {* max 1000} min} ; output will be best if smaller is
 }}}}                           ; no more than two digits