SURVIVALCRAFT 2 WIKI CODE
Since the definition is machine executables (calls), mcahine code itself may be inserted into the definition, interspersed within the predefined words. This model allows for features not available in the other threading models. Rather than a sequence of calls to other words, it is just machine code. Furthermore, even each primitive is a simple subroutine. If the hardware supports nested subroutines, this is a very efficient model. In a subroutine threaded execution model, the definition of each (non-primitive) word is a subroutine call. This design uses a subroutine threaded execution model. These are usually called direct, indirect, subroutine and token threaded models. Several types of threaded execution models have been developed, usually because of limitations of the underlying hardware. The mechanism that keeps track of and controls this threading (and thus the program's execution) is called the inner interpreter. It is this threading that allows the language itself to grow with each newly defined word (or command). Thus the term 'threading' is used to describe this means of execution. Each of those words is executed in the proper order as well before continuing on with the following word in the primary command. As each word in this definition is executed, it also may be a sequence of other words. A command is executed by simply executing each word in its definition, in the defined order. The most basic of these words are written in machine code rather than by using other words. A program or function or command is initiated just by 'calling' its name. In a threaded language each command or word, is defined by a sequence of previously defined commands.
Hence, Forth is 'infinitely' extensible.Ī threaded language is quite different than the more commonly known types (which can trace their roots back to Algol). These new words may be used in other parts of the code, effectively extending the language's commands. These are allowed to execute on the CPU core and the definition tree is followed again until the end of the word being executed is reached.Įach new 'word' becomes a new language command, or what other languages may call a 'reserved word'. The inner interpreter continues through the indirection of defined words until it reaches the level of 'primitives' - that is, words that are defined in machine code. The outer interpreter is what gives Forth its interactivity since it can accept input directly from the console. Assuming it is found, the definition of the found word is then passed to the 'inner interpreter' to be executed. Forth uses two interpreters - the 'outer interpreter' takes the new word's definition and looks for each word included in that definition.
Once the code is complete, it may be completely compiled and loaded into the system. That is the great benefit to an interpreted language. This way it can be tested without even a re-compile step.
SURVIVALCRAFT 2 WIKI SOFTWARE
This interactivity makes testing both the hardware and software very easy and allows errors to be caught asap.Ī new word's definition may simply be typed out into the console and immediately executed.
As soon as a new word is written, it may be tested since most Forth systems include a built-in interpreter.
SURVIVALCRAFT 2 WIKI SERIES
New words are either a sequence of machine code commands or a series of previously defined words. Programs written in Forth are written in small routines called 'words'. It has its roots in small, fast embedded systems and enjoys great success in those types of applications to this day. These are included for completeness and to provide a familiarity to assembler/machine level programming.įorth is an interpreted/compiled, extensible, interactive language which is quite unlike any other popular language. The design also included other resources not needed to support Forth but which are generally assumed for other languages. This tool is the Forth language.Ī complete description of Forth will not be included here, but its highlights and applicability to this design are discussed below. It is often called a programmer's tool, rather than a language because it's actually much more than what is understood as a programming language. However, there is an uncommon "high level language" that was designed specifically for resource restricted devices. In addition to the resources and codespace a high level language needs, there would also have to be a custom compiler and/or an assembler written for this design. In fact, the amount of support required for any common high level language would be a tremendous burden. It may be nearly unthinkable that a small system in such an atypical environment should support a high level programming language.
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