A string based bison parser

This project has been made for the formal languages and translators course ("LFT" in romanian). It is basically a C based parser that support various operators for strings.

Compiling and running the program

Let's get the important things out of the way. For this program to work you obviously need to have flex, bison and gcc installed. This usually is not a problem since most linux distributions come with flex and bison preinstalled since they are part of the GNU Project. gcc is also usually installed, but if it's not you need to install it.

Another requirement just for the Abstract Syntax Tree (AST) representation is that you need to have the utility called dot. You can install it by installing the graphviz package on your distro.

That is all in terms of requirements, now on how to run the program (I will add a Makefile later, so this becomes easier):

1. bison -d parser.y (This will generate the header and c files for the parser)
2. flex lexer.l (will genereate the lex.yy.c file which will be needed for lexical analysis)
3. gcc -o parser_interpret parser.tab.c lex.yy.c interpret.c -lfl (this will generate the executable parser_interpret which will be the interpretative version of parsing code)

The executable accepts two arguments, <input_file> and <output_file, if no arguments are given stdin is taken as input

For the graph version you would need to run the following

1. Generate bison and flex files like in the interpretative version
2. gcc -o parser_graph parser.tab.c lex.yy.c graph.c -lfl

The graph version take in one positional argument and that is <input file> and it will output both the .dot file for the graphs and a png with all the graphs generated from each line

Alternatively you can run the make command to build both versions, make interpreter just for the interpreter version, make graph just for the graph version. make clean removes all the generated files.

Specs/Syntax

Like I said the syntax is relatively simple being quite similar to C/C++ syntax

Variable declaration:

A variable is declared much like in C:

a="abc"; This assigns the string literal abc to variable a. Like I said pretty self-explanatory

Variables can also take on the values of other variables. Like this:

a="abc";
b=a;

this piece of code will assign the value of variable a to variable b;

To note is that variables can be only single uppercase or lowercase character since that was the requirement of the project

Print statement

As anyone could've guessed print just prints out the value of an expression, for example

a="abc";
b=a;
print b;

will print out to our stdout the value abc.

Print can be used in conjuction with any kind of expression (like the ones discussed after this)

String concatenation

String concatenation is also done very simylarly to C using the + operator

a="abc";
b=a+"de";
print b;

will print out abcde

String substraction

String substraction works with the - operator and is of form <str1> - <str2> and what it will do is, it will remove ALL the instances of <str2> from <str1> (if there are any)

a="abc";
b=a-"b";
print b;

will print ac

Case operator

The case operator is ^ and is of form ^<str> and it will return <str> with all it's characters switched in case (i.e lowercase become uppercase and vice-versa)

a="aBc";
b=^a;
print b;

will print AbC

Length operator

The length operator is ~ and is of form ~<str> and it will return the length that the string has with spaces

a="hello world";
print ~a;

will print 11

Increment and decrement

The increment and increment operator work much the same like in C and have the same form, i.e can be postfixed and prefixed with all the same quirks. They are of form ++<str> and will increment the first character of the string

a="abc";
a++;
print a;

will print bbc;

Beginning and End char operators

The language also has two other operators # and /, of form <str>#<num>. In the case of # it will return the first <num> characters of the string, while / will return the last <num> characters

a="abc";
print a#2;
print a/1;

will print ab and c respectively

Comparators

The comparison operators are the same like in any other language, where it will <,>,<=,>= will compare the string lexico-graphically, i.e length, and ==,!= will compare lexico-graphically and content wise the strings. It will return true if the condition is met, else false

a="abc";
b="abcd";
print a<b;

will print true