This is an implementation of the UO Steam scripting language. The interpreter is not tied to any particular program, but is instead extensible through the registration of command handlers. By default, all of the handlers print they were executed to the console.

To run a test of the interpreter, first build it. The output will consist of a library named UOSteam.dll and an application called Tester.exe. The Tester.exe application currently expects a file named "test.uos" containing a Steam script in the same directory as the executable. You can try various valid Steam scripts and it will first print the parsed abstract syntax tree for the script, then execute it.

TODO:

• Lists
• Aliases

Steam Script Overview

The full documentation for the Steam scripting language is located here. While that outlines the valid syntax, the following will break the language down at a more technical level. Here is an example Steam script.

msg 'Hello'
if @findtype '0x1bdd' 'any' 'backpack' 'any' 'any'
  @setalias 'Logs' 'Found'
  useobject 'Axe'
  autotargetobject 'Logs'
  pause 1000
endif

Most lines in a Steam script are called Commands. They simply execute some action (e.g. msg 'Hello'). The first word (ignoring modifiers such as @) represents the command and the remaining tokens are the arguments to that command.

Some lines instead contain control-flow statements such as if, for, while, and their associated end-statements like endif. Following a control-flow statement comes an Expression. In the above example, @findtype '0x1bdd' 'any' 'backpack' 'any' 'any' is an expression. Expressions come in two types - unary and binary. The previous example is a unary expression. A binary expression contains a comparison operator such as hits < 100. For unary expressions, the first token (ignoring modifiers such as @) in the expression is the expression type and the remaining tokens are arguments. For binary expressions, everything is treated as an alias or value.

The final major primitive is an Alias. Aliases are human-readable names for values, such as any and backpack. An alias always evaluates to a value. Many aliases always exist when a Steam script runs, but additionally a user may create their own aliases using the setalias command. Users may only set aliases to serial numbers - not to any other value type.

Design

The solution consists of two projects. Tester is a test application that runs steam scripts for testing purposes. UOSteam is an assembly that contains the actual interpreter.

The UOSteam interpreter itself is only two files:

• Lexer.cs contains the Lexer (sometimes called a parser). The Lexer class has a single public function Lex that takes the raw script input and parses it into an Abstract Syntax Tree. It returns the root of the tree.
• Interpreter.cs contains two classes. The Script class represents one Steam script. The constructor requires the root node of an abstract syntax tree. The Interpreter class represents an entire interpreter. This is necessary because some aliases are global - their values are visible across all scripts executing now and into the future.

Neither the interpreter nor the parser actually know which Commands, Expressions, and Aliases are actually valid. Instead, the Interpreter class has methods for registering handlers for any command, expression, and alias necessary.

The Tester application contains a file called Commands.cs that registers handlers for all of the standard Steam Commands, Expressions, and Aliases. This handler, however, simply prints to the console so that we know they executed. When integrating this Steam interpreter into a real application, you're expected to register your own handlers that take the appropriate actions.