Syntax

Gravity syntax is designed to be familiar to people coming from C-like languages like Javascript, Swift, C++, C# and many more. We started working on this new language a year before Apple announced Swift and we were happily surprised to discovered how similar both syntax appear.

In Gravity semicolon separator ; is completely optional.

What Gravity code looks like:

    class Rectangle {
        // instance variables
        var width;
        var height;

        // instance method
        func area() {
            return width*height;
        }

        // constructor
        func init(w, h) {
            width = w;
            height = h;
        }
    }

    func main() {
        // initialize a new Rectangle object
        var r = Rectangle(20, 10);

        // return value is 20*10 = 200
        return r.area();
    }

Comments

Gravity supports both line comments:

    // This is a line comment

and block comments:

    /*
        This
        is
        a
        multi-line
        comment
    */

While Gravity uses C-Style comments, Gravity still supports the common "#!" shebang to tell your shell what program to execute the file with. However, the shebang must be on the first line of the file in order to use it in this way:

    #!/path/to/gravity

    func main() {
        System.print("Execute as: path/to/file.gravity");
        System.print("Instead of: gravity path/to/file.gravity");
    }

Include

To statically include a gravity file from within another gravity file you can use the #include statement. Please note that in the current version, the path to the included file is relative to the location that the gravity executable was run.

    // adder.gravity
    func add(x, y) {
        return x+y;
    }

    // main.gravity
    #include "adder.gravity"

    func main() {
        System.print("5+4=" + add(5,4));
    }

Import

While #include is used to include file at compilation time, the import statement enables you to load modules at runtime. Import is under active development and it will be available pretty soon.

Reserved Keywords

Like many other programming languages Gravity has some reserved keywords that assume a very specific meaning in the context of the source code:

    if in or is for var and not func else true enum case null
    file lazy super false break while class const event _func
    _args struct repeat switch return public static extern
    import module default private continue internal undefined

Identifiers

Identifiers represent a naming rule used to identify objects inside your source code. Gravity is a case-sensitive language. Identifiers start with a letter or underscore and may contain letters, digits, and underscores (function identifiers can be any of the built-in operators in order to override a default behaviour):

    a
    _thisIsValid
    Hello_World
    foo123
    BYE_BYE

Blocks and Scope

Every named identifier introduced in some portion of the source code is introduced in a scope. The scope is the largest part of the source code in which that identifier is valid. The names declared by a declaration are introduced into a specific scope based on the context of the declaration. For instance, local variable declarations introduce the name into the block scope, whereas class member variable declarations introduce the name into class scope.

There are three scopes defined: block scope, class scope and file scope. Names declared in the block scope become visible immediately after its completed declarator. This means you cannot refer to a name within the block scope until after it has been fully declared. Names declared in the file and class scopes become visible immediately upon executing the starting statement of the script. This means you can refer to a name within the file or class scopes before it has been fully declared.

These are all valid scopes:

    // file scope can refer to a name
    // before it has been fully declared
    func f1() {
        return f2();
    }
    func f2() {
        return 42;
    }

    // block scope can be nested and
    // can hide other local variables
    func f3() {
        var a = 10;
        if (a > 0) {
            var a = 20;
        }
        // 10 is returned here
        return a;
    }