README.md

Analyzer

Parser & interpreter for a custom programming language. This project was made for study and research about compiler construction.

Why "Analyzer"?

1. I'm bad at naming things.
2. This project began as a lexical analysis tool; the parser and interpreter were added later on. I may rename it in the future

Dependencies

1. Maven
2. jflex 1.9
3. cup 11b

Build

Run maven compile to generate the lexer & parser classes. The resulting java files should be inside of ${project.build.directory}/generated-sources. Mark that folder as "Generated Sources Root" (if you're using IntelliJ).

Run the interpreter

Navigate to src/main/java/org/automatas/program/Main.java and edit the main method.

Edit it to set your custom path to a source file (eg: engine.executeFile("path/to/source.txt")).

code.txt contains a sample code that can be run by the interpreter.

Run the main() method and done!

Types

The language supports these primitive types:

1. array (java.util.ArrayList)
2. bool (java.lang.Boolean)
3. float (java.lang.Double)
4. int (java.lang.Long)
5. string (java.lang.String)

Numeric literals can be expressed in various forms:

• Bin: 0b00001010
• Hex: 0xffa500
• Oct: 0o276
• Exp: 1.30e5

Comments

// This is a line comment.

/*
    And this is a
    block comment.
 */

Variables

Declaring a variable

Use the := operator (borrowed from Go) to declare a new variable in the current scope.

var := "Hello";

The interpreter will throw a fatal error if you attempt to re-declare a variable within the same scope.

var := "Again!"; // Fatal Error: 'var' is already defined.

However, you can declare a variable with the same identifier (name) within a nested scope.

var := "Outer";

{
    // This is allowed, as the inner-most variable
    // shadows the variable in the parent scope.
    var := "Inner";
    print(var);
}

print(var);

Using a variable

Variables can be re-assigned with the = operator.

var = "Hello there";
print(var);

And the interpreter will throw a fatal error if the variable is undefined.

unknown = "???"; // Fatal Error: undefined variable 'unknown'.

Variables can store any type of value at any moment:

var = [1, 2, 3];
var = true;
var = 3.1415;
var = 2023;
var = "A113";

The is operator checks if the given value is of a specific type, while the as operator casts the value from one type to another:

// Check if the value is a string
if var is string {

   // Cast to integer
   casted := var as int;

}

Use the unset operator to remove a variable:

unset var;
print(var); // Fatal Error: undefined variable 'var'.

Arrays follow the usual bracket-style syntax:

arr := ["a", "b", "c"];
val := arr[1];
arr[0] = "x";

Arrays grow dynamically, so you can append values by using the [] syntax (borrowed from PHP):

arr := []; // Empty array
arr[] = "hi"; // Append a string (note that you have to use = operator).
print(arr[0]);

And with the unset operator, you can remove one value from the array (the array will be re-indexed):

arr := ["a", "b", "c"];

print(arr[0]); // "a"
unset arr[0];
print(arr[0]); // "b"

Logic operators

Operator	Meaning
expr && expr	and
expr || expr	or
!expr	not

Relational operators

Operator	Meaning
expr == expr	equal
expr != expr	not equal
expr < expr	less
expr <= expr	less or equal
expr > expr	greater
expr >= expr	greater or equal

Arithmetic operators

Operator	Meaning
expr + expr	addition / concatenation
expr - expr	subtraction
expr * expr	multiplication
expr / expr	division
expr % expr	modulo
expr ** expr	exponentiation

Control structures

If/Else

The if/else statement looks like this:

if condition {
    /* if-statements */
}

if condition {
    /* if-statements */
} else {
    /* else-statements */
}

Note that the condition doesn't require parenthesis.

While / For

while condition {
    /* while-statements */
}

for declaration; condition; step {
    /* for-statements */
}

There's no break or continue keywords yet.

BuiltIn functions

print prints to STDOUT followed by a \n.

printf prints a formatted string to STDOUT.

input gets input from STDIN optionally printing a prompt message.

print("This program tells you if your number is even or odd.");

number := input("Number: ") as int;

if number % 2 == 0 {
    printf("Your number %d is even!\n", number);
} else {
    printf("Your number %d is odd!\n", number);
}

Functions

Using the fn keyword you can declare your own functions!

fn fib(n)
{
    if n <= 1 {
        return n;
    }

    return fib(n - 1) + fib(n - 2);
}

n := fib(10);
printf("Fibonacci of 10 is: %d\n", n);