Introduction to Genie

This guide is a general introduction to the Genie programming language and a walk-through of its syntax. It is a port of the official Genie tutorial that was previously hosted on the GNOME Wiki. The same material is split into chapters so you can read or link to smaller sections.

What is Genie?

Genie is a programming language, in the same vein as Vala. Genie allows for a more modern programming style while being able to effortlessly create and use GObjects natively on Linux, *BSD, Windows or macOS.

The syntax is designed to be clean, clear and concise, and is derived from numerous modern languages like Python, Boo, D and Object Pascal.

Genie is very similar to Vala in functionality but differs in syntax, allowing the developer to use cleaner and less code to accomplish the same task.

Like Vala, Genie has the following advantages:

• Programs written in Genie have similar performance and resource usage to those written directly in Vala and C.
• Genie produces C code that compiles to an executable binary. This means Genie has none of the bloat and overhead that comes with many other high-level languages which utilize a VM (e.g. Python, Mono, Java).
• Classes in Genie are actually GObjects, so Genie can be used for creating platform code like widgets and libraries where GObjects are required for binding to other languages.

Hello World

As Hello World is the de facto first sample program, here is Genie's in all its glory:

init
    print "Hello World"

Provided you have Vala installed, copy and paste the code above and save it in a file called hello.gs. Genie code must be written in files with the *.gs extension.

Compile and run it by simply issuing the following on a UNIX-like command line in the same directory you saved hello.gs:

$ valac hello.gs
$ ./hello

When you want to compile Genie code, you give the compiler a list of the files required, and the Genie/Vala compiler will work out how they fit together.

If you give valac the -C switch, it will create a C source code file called hello.c instead of an executable binary file.

Hello World Explained

As you can see, Genie is pretty clean and concise so the above example will not need much explaining.

init Block

An init block declared outside of a class or struct is equivalent to a main function in C and only one of these may be present. Any code that needs to be run at start up should be present here.

Block Indentation

Block indentation in Genie uses tabs by default. So in the Hello World example above, a tab appears prior to the keyword print.

It is also possible to tell it to use a certain number of spaces in lieu of a tab by ensuring the first line of the source file contains the following attribute:

[indent=2]
init
  print "Hello World"

That attribute tells Genie to ignore tabs and use 2 spaces to signify a block indentation. An indent=0 means use a tab.

Code examples on this page use spaces for indentation because the original wiki converts tabs to spaces. When writing your own Genie programs use tabs unless you have set the [indent=N] attribute.

Case and Unicode

Genie is case sensitive, so be careful when mixing case in your code. Keywords are always lowercase. Identifiers can be mixed case, but must be in the Unicode U+0020 to U+007E range. This is the ASCII printable characters range as a result of it being compiled into C code. For example:

init
    pi:double = Math.PI
    print pi.to_string()

would compile, but

init
    π:double = Math.PI
    print π.to_string()

would produce an error because the symbol π is outside the ASCII printable range of characters.

Genie can, however, handle Unicode data very well. Here is an example of Hello World with Unicode characters outside the ASCII range:

init
    Intl.setlocale( LocaleCategory.ALL, "" )
    print "Hello World! 你好世界"

C libraries use the US English, ASCII encoding, by default as part of the C standard. The setlocale command changes this to the locale of the machine and if this can handle Unicode and has Chinese glyphs installed then the Chinese version of Hello World will be displayed.

Chapters

1. Compiling and Genie's relation to C — VAPI, build scripts, static checks, and generated C
2. Language basics — documentation style, identifiers, values, operators, control flow, scope
3. Types, functions, and errors — delegates, classes, generics, functions, try / except
4. Objects — fields, constructors, properties, methods, signals, inheritance
5. Collections and C interoperability — operators, collections, C bindings
6. Concurrency, IPC, and system interfaces — async, D-Bus, pipes, signals, UIs
7. Advanced topics — attributes, memory, mixing Genie and Vala, further reading