--------------------------------------------------------------------
--                        a3.ads

-- This file is the specification file for the types
--    and functions used in the recursive descent
--    parser of Assignment 3, CS 152, Fall 2000.

--------------------------------------------------------------------

with TEXT_IO;    use TEXT_IO;

package a3 is


-- These types, procedures, and functions
--    make up the interface with the test program.  
-- Note that the parse tree is known to be
--   represented by a pointer.

type parse_tree is private;
type parse_tree_ptr is access parse_tree;


-- This function takes the name of a text file, attempts
--    to parse the tree using the grammar implemented
--    by the parser, and returns a parse tree for the
--    text in the file.  It returns a dummy tree if the file is
--    not found, or the text cannot be parsed.  It returns
--    an appropriate error message in case either of
--    these errors occurs.

function parse(filename:string) return parse_tree_ptr;

-- This function prints an indented representation
--   of an ordered tree, one line per node. 

procedure traverse(p:parse_tree_ptr);


-- This function prints the yield of a parse tree (that is, it
--   traverses the leaves).  All data is printed on one line.

procedure display_yield(p:parse_tree_ptr);
   


private

-- your material goes here



end a3;