Name: Hudson Shykowski & Dale Richmond Naviza
ID : 1520045 & 1534579
CMPUT 275, Winter 2019
Final Assignment: P- programming language

Dependencies:
    - Boost version 1.66.0 is required to compile this program

Description:

    The P- programming language is a simple language built with the intent
    of teaching new programmers the basics of graphs. The three data types in
    P- are integers, strings and graphs. There are many graph functions,
    all of which are defined in digraph.h.

    In order to create this programming language, 3 main components were required.

    1. Lexer
        The lexer simply splits the P- source code file into it's tokens.
        It then classifies every token into it's respective lexical type.
        Any token that does not fit a given lexical type is assumed to be
        an identifier

    2. Context free grammar parser
        The context free grammar checking is implemented according to the Cocke–Younger–Kasami algorithm. makeGrammar() creates an unordered
        map that describes the grammar in Chomsky Normal Form. The function
        CYK() in grammar.cpp checks if a given line is valid according to
        different grammars for diffent "Start" nonterminals. More information
        about the grammar syntax is in grammarTest.txt which is the grammar
        that is fed into the program

    3. Transpiler
        Once the grammar has been verified, the transpiler converts the
        P- code into C++ code. As it converts the code line by line,
        it builds a list of defined identifiers which it uses to ensure
        that undeclared identifiers are not used illegally, and that
        type reassignment does not occur. Once the entire P- code has been converted,
        the C++ compiler converts the C++ code into an executable.

Running Instructions:

    1. To compile and link, run "make"
    2. Run the executable exercise4 with "./main"
    3. If the code is valid syntax, "./main" will generate an
       executable called "program". Run "./program" to see the result
       of your P- program
    4. To delete the executables, run "make clean"


Note and assumptions:

    - Most of the code in digraph.cpp and digraph.h was taken from eclass
      and so was not commented. However, the digraph class was augmented
      to include a "string" value contained in each node, and comments
      related to this was included in digraph.cpp and digraph.h

    - The else if statements in lexer.cpp were left on their own lines
      in order to improve readability of the code

    - A lot of research was done for the Context Free Grammar. The sources
      were cited above the functions where they were implemented.