Screet

Screet is an embeddable object-oriented scripting language.

Screet is designed to be embedded in a larger program, providing an object-orient interpreter to inspect and control aspects of the program. The interpreter currently compiles to well under 100K of object code on x86.

Screet can also operate on Woosh objects. The screet-woosh program provides a command-line environment for evaluating Screet expressions on Woosh objects. It also provides a way to write Woosh methods in Screet.

Object Model and Syntax

All Screet expressions yield strings. However, when performing a function call, some strings are treated specially: strings representing numbers are treated as numbers, and strings beginning with certain special prefixes are treated as objects and error values.

Most expressions will be function calls. The most basic syntax for function calls looks like object.function(argument-1, argument-2) . Function calls with no arguments don't need the parentheses -- object.function is the same as object.function() . The usual suite of C operators is also available (with C's precedence rules); these are also treated as function calls. There is also an alternate function call syntax that resembles a CLI: object function argument-1 argument-2 .

There are also assignment expressions: variable = expression . The variable is created if it doesn't already exist. There is only a global scope. If Screet is embedded, the enclosing program may predefine variables; screet-woosh makes all Woosh objects available as variables. Variable names may contain hyphens (and are encouraged to), but not at the beginning or end.

Other expressions are literals -- string literals, numbers, true, false, and nil (false and nil are both the empty string).

There are also statements. Currently only if statements and compound statements ( { expression; expression; } ) are implemented. Statements are actually expressions too; an if statement yields the value of the chosen branch, and a compound statement yields its last expression.

The complete syntax is described in the "syntax.txt" file in the tarball. But not everything works the way it's supposed to at the moment.

Embedding Screet

The easiest way is to include ScreetMethodCall.Screetable.cpp in your project (along the rest of the files from the tarball, except Main.cpp and WooshContext.cpp), and make the classes to which you want to have access be subclasses of Screetable, defining screetCall() functions for them.

You can create a ScreetListener object and call its listen() function to have it listen on a TCP socket. Do this in a separate thread -- it doesn't return. Use the screet-to program ("make screet-to" to build it) to connect to it and have it evaluate expressions.

See Main.cpp for examples.

Screet and Woosh

Build screet-woosh by doing "make clean && make screet-woosh". (You have to make clean anytime you switch between screet-woosh and other make targets, since different compiler options are used.) Put screet-woosh somewhere in your $PATH.

Running screet-woosh with no arguments gives you a command line at which you can type expressions and see the results. (Like bash, screet-woosh uses the readline library to provide editing and history.)

You can also write Woosh methods in Screet. Here's an example:

#!/usr/bin/env screet-woosh

{
  if (arg-1 == "Yes")
    some-object.some-method();
  else
    "Sorry, " + arg-1 + " isn't Yes.";
}

Downloading Screet

Contact Info

Send bug reports, etc. to steve@folta.net.