What is goo?

goo v. colloq. a viscid or sticky substance; sentimental tripe;
object oriented language for use in unix applications.

goo is being designed by Robey Pointer, with help from Scott James Remnant and Greg Brown. The goo compiler and libgoo library are being written by Robey in his spare time.

What makes goo different from other embeddable script langauges?

• goo is meant to be used by many users at once. Each user has their own namespace and can set permissions on their classes and objects, such that one user can design a class and then permit (or deny) other users to use the class or even create derivatives of it.

• A goo class can be loaded, used, and then changed and reloaded without having to change the underlying application at all. This allows users to fix bugs in their classes or even expand them without affecting others (even if other people are currently using or deriving from that class).

• All goo classes and objects are persistent -- serialized and saved to a backing store, much like a database. The goo "world" can be distributed across many machines, with objects migrating between machines (accessible to all).

What did goo steal from its predecessors?

The original purpose of goo was to create a script language that could be used as the engine for a MUD (multiuser text game). We looked at using Perl or Java, but neither language supported everything we needed.

Perl supports OO only as a last-minute addition, sort of nailed onto the side, and doesn't enforce any of the class attributes. Java does a lot of what we wanted, but doesn't support multi-user operation or allow classes to be reloaded after being modified.

As a result, goo is strongly influenced by both Perl and Java, as well as drawing from Tcl, Ada, and C++. Some features we pulled from these languages include:

• Arrays and hashes are builtin constructs, as in Perl. Also, strings and numbers are grouped together as a single variable type ("scalar").

• Function parameters are named, as in Ada. When calling a function, you may either give the parameters positionally (the standard way, like C) or give them in any order and name them. This allows you to arbitrarily omit parameters (all parameters have default values), which is surprisingly useful for constructors, and removes the need for function overloading.

• goo uses single inheritence with "interfaces", a concept grabbed wholesale from Java. All objects have a known "real" type, regardless of what type they're being used as, and this type can be queried at runtime using "is" and "as" operators:

  if (obj is TreeHouse)

  or

  (obj as TreeHouse).openDoor()

• A class may be implemented entirely in C code, linked in via shared library, much like in Tcl or Perl.

• Exceptions and "finally" blocks are supported, but don't require a "try" block (which makes them closer to Tcl in this respect than to Java). Any data type (including scalar) can be thrown, as in C++. Catch and finally blocks apply to the code block they're enclosed in.

• Garbage collection is done, as in most interpreted languages. A form of byte-code compilation is also done, similar to Perl & Java, to keep the runtime as streamlined as possible.

• Array and string "slices" are ripped off from Python, syntax and all.

Where can I get it?

Right now you can't, but soon enough you can. Our current plans are to release it under the GNU GPL. The test application "Mr. Sparkle" is currently (as of Mar 1999) parsing, compiling, and executing basic goo code.

However, for the curious of you, we have released the "goo spec". This is the document we use to draft out the language (usually only slightly out of date with respect to the goo code).

Where can I make comments or ask Questions?

If you have any comments or questions about goo then e-mail Robey Pointer at robey@lag.net.

Misc. Documentation

• A description of how cross-machine objects and garbage collection will work.

• A text goo specification that's usually more-or-less current.