LISP (List Processing) is a family of programming languages where the program is composed solely of linked lists.

Each list in any Lisp dialect is surrounded by parentheses, with the elements delimited by spaces (and ordered from left to right). The first element is assumed to be the function, and the remaining elements are the parameters to this function. A list of this form is also called an s-expression.

For example:
(+ 1 2 3)
Is a simple program in Lisp which would evaluate to 6

An atomic list is a list that contains no other lists. Your goal is to implement addition, multiplication, and subtraction over atomic lists according to the specified interface.

This should be an extension of Lab 4, however the main method will now be in the class you create for this assignment, and not in Lisp.java.

Write a class called Parser which will be responsible for parsing compound s-expressions into atomic s-expressions.

Your class must do the following:

• Define the following non-static methods:
  • getSexp Finds the next atomic s-expression in the file.
    • params
      • repl: An instance of a class implementing Repl. You should have already completed this in Lab 4, so you may use the class you have written for that assignment.
      • scan: A Scanner over some s-expressions. We will be using a Scanner(File) for this assignment.
      • parenCount: The (integer) number of unmatched parentheses encountered so far.
    • return An atomic s-expression as a String
• A main method that asks the user to enter a file to parse, then calls getSexp on a Scanner over that file.

A good strategy is to parse the file character by character, and build up the s-expression as a String. Done this way, you have 4 cases to consider:

• The character is '('
  In this case you have found a nested s-expression, so you should make a recursive call to getSexp. Make sure to update the parameters as appropriate.
• The character is ')'
  In this case you are closing off the s-expression. Do any necessary updates to the string and pass off the s-expr to your eval method from Lab 4's Lisp class. Then return this result.
• The character is whitespace ('\n', '\t', or ' ')
  You may want to make it easy on your read and convert all whitespace to a single space for ease of parsing later.
• Otherwise
  Add the current character to the s-expression you are building

In addition, you might find the following methods useful:

• «scanner».useDelimiter("")
  Force the scanner to have no delimiter, so every call to next returns only the next character.
• «string».replaceAll(" +", " ")
  Replace multiple instances of a space with a single space in the given string.
• «string».replaceAll(" \\)", "\\)")
  Replace the sequence ' )' with a single closing bracket ')' in the given string.
• «string».replaceAll("\\( ", "\\(")
  Replace the sequence '( ' with a single closing bracket '(' in the given string.

        Enter the name of a lisp file
        test.lisp
        6
        8
        16
    

Upload the .java file to the dropbox