• Show a few examples of abstract syntax tree nodes for the language of Assignment 1.

  Example:

                             +
                            /  \
                           a    b
  

  is an AST node for a + b. In parenthesized form, this could be written:

  ( + ( a b ) )
  
  

• Define a set of abstract syntax tree nodes for the language of Assignment 3.

  Examples:

           if                                  while
          /   \                               /    \
         >    :=                             <      ;
       /  \  /  \                          /  \    /  \
      a   b  m   2                        a    b  :=  :=
                                                 / \  /  \
                                                a  2  b  1
  
         AST for:                             AST for:
     if a < b then m := 2                  while a < b do begin
                                              a := 2;
                                              b := 1
                                           end
  

  (Note the "dummy" node ";" which links statements in the same begin..end block together. Such things are unavoidable.) In parenthesized form, the second tree would be written as,

  (while (< (a b)) (; (:= (a 2)) (:= (b 1))))
  
  

• Modify your parser to translate input programs into AST's. Run your program with (i) the program of assignment #1, (ii) the programs of assignment #3, and (iii) a program of your choice. Print out the AST in some reasonably readable form, using parentheses as above, and indenting lower levels of the tree. (You need no longer print out tokens and parse info, although for future debugging purposes you are well-advised to merely comment those statements out).

Back to CS 230 Home Page