cubed4th
FORTH^3, relicensed with permission from https://github.com/p-unity
-- THE FORTH-79 STANDARD --
The folling text was performed by OCR and contains may mistakes. Feel free to submit corrections.
DEFINITIONS OF TERMS
These definitions, when in lower case, are terms used within this Standard. They present terms as specifically used within FORTH.
A
address, byte
An unsigned number that locates an 8-bit byte in a standard FORTH address space over {0..65,535}. It may be a native machine address or a representation on a virtual machine, locating the 'addr-th' byte within the virtual byte address space. Address arithmetic is modulo 65,536 without overflow.
address, compilation
The numerical value equivalent to a FORTH word definition, which is compiled for that definition. The address interpreter uses this value to locate the machine code corresponding to each definition. (May also be called the code field address.)
address, native machine
The natural address representation of the host computer.
address, parameter field
The address of the first byte of memory associated with a word definition for the storage of compilation addresses (in a colon-definition), numeric data and text characters.
arithmetic
All integer arithmetic is performed with signed 16 or 32 bit two's complement results, unless noted.
B
block
The unit of data from mass storage, referenced by block number. A block must contain 1024 bytes regardless of the minimum data unit read/written from mass storage. The translation from block number to device and physical record is a function of the implementation.
block buffer
A memory area where a mass storage block is maintained.
byte
An assembly of 8 bits. In reference to memory, it is the storage capacity for 8 bits.
C
cell
A 16-bit memory location. The n-th cell contains the 2n-th and (2n+1)-th byte of the FORTH address space. The byte order is presently unspecified.
character
A 7-bit number which represents a terminal character. The ASCII character set is considered standard. When contained in a larger field, the higher order bits are zero.
compilation
The action of accepting text words from the input stream and placing corresponding compilation addresses in a new dictionary entry.
D
defining word
A word that, when executed, creates a new dictionary entry. The new word name is taken from the input stream. If the input stream is exhausted before the new name is available, an error condition exists. Common defining words are: : CONSTANT CREATE
definition
See 'word definition'.
dictionary
A structure of word definitions in a computer memory. In systems with a text interpreter, the dictionary entries are organized in vocabularies to enable location by name. The dictionary is extensible, growing toward high memory.
E
equivalent execution
For the execution of a standard program, a set of non-tine dependent inputs will produce the same non-time dependent outputs on any FORTH Standard System with sufficient resources to execute the program. Only standard source code will be transportable.
error condition
An exceptional condition which requires action by the system other than the expected function. Actions may be:
- ignore, and continue
- display a message
- execute a particular word
- interpret a block
- return control to the text interpreter
A Standard System shall be provided with a tabulation of the action taken for all specified error conditions. General error conditions:
- input stream exhausted before a required .
- empty stack and full stack for the text interpreter.
- an unknown word, not a valid number for the text interpreter.
- compilation of incorrectly nested conditionals.
- interpretation of words restricted to compilation.
- FORGETing within the system to a point that removes a word required for correct execution.
- insufficient space remaining in the dictionary.
F
false
A zero number represents the false condition flag.
flag
A number that may have two logical states, zero and non-zero. These are named 'true' = non-zero, and 'false' = zero. Standard word definitions leave 1 for true, 0 for false.
G
glossary
A set of word definitions given in a natural language describing the corresponding computer execution action.
H
I
immediate word
A word defined to automatically execute when encountered during compilation, which handles exception cases to the usual compilation. See IF LITERAL ." etc.
input stream
A sequence of characters available to the system, for processing by the text interpreter. The input stream conventionally may be taken from a terminal (via the terminal input buffer) and mass storage (via a block buffer). >IN and BLK specify the input stream. Words using or altering >IN and BLK are responsible for maintaining and restoring control of the input stream.
interpreter, address
The (set of) word definitions which interprets (sequences of) FORTH compilation addresses by executing the word definition specified for each one.
interpreter, text
The (set of) word definitions that repeatedly accepts a word name from the input stream, locates the corresponding dictionary entry, and starts the address interpreter to execute it. Text in the input stream interpreted as a number leaves the corresponding value on the data stack. When in the compile mode, the addresses of FORTH words are compiled into the dictionary for later interpretation by the address interpreter. In this case, numbers are compiled, to be placed on the data stack when later interpreted. Numbers shall be accepted unsigned or negatively signed, according to BASE.
J
K
L
load
The acceptance of text from a mass storage device and execution of the dictionary definition of the words encountered. This is the general method for compilation of new definitions into the dictionary.
M
mass storage
Data is read from mass storage in the form of 1024 byte blocks. This data is held in block buffers. When indicated as UPDATEd (modified) data will be ultimately written to mass storage.
N
number
When values exist within a larger field, the high order bits are zero. When stored in memory the byte order of a number is unspecified.
type range minimum field
bit 0..1 1
character 0..1277
byte 0..2558
number -32,768..32,76716
positive number0..32,767 16
unsigned numberO..65,535 16
double number -2,147,483,648..
2,147,483,647 32
positive double number 0..2,147,483,647 32
unsigned double number 0..4,294,967,295 32
When represented on the stack, the higher 16-bits (with sign) of a double number are most accessible. When in memory the higher 16-bits are at the lower address. Storage extends over four bytes toward high memory. The byte order within each 16 -bit field is unspecified.
O
output, pictured
The use of numeric output primitives, which convert numerical values into text strings. The operators are used in a sequence which resembles a symbolic 'picture' of the desired text format. Conversion proceeds from low digit to high, from high memory to low.
P
program
A complete specification of execution to achieve a specific function (application task) expressed in FORTH source code form.
Q
R
return
The means of terminating text from the input stream. (Conventionally a null (ASCII 0) indicates end of text in the input stream. This character is left by the 'return' key actuation of the operator's terminal, as an absolute stopper to text interpretation.)
S
screen
Textual data arranged for editing. By convention, a screen consists of 16 lines (numbered 0 thru 15) of 64 characters each. Screens usually contain program source text, but may be used to view mass storage data. The first byte of a screen occupies the first byte of a mass storage block, which is the beginning point for text interpretation during a load.
source definition
Text consisting of word names suitable for execution by the text interpreter. Such text is usually arranged in screens and maintained on a mass storage device.
stack, data
A last in, first out list consisting of 16-bit binary values. This stack is primarily used to hold intermediate values during execution of word definitions. Stack values may represent numbers, characters, addresses, boolean values, etc.
When the name 'stack' is used, it implies the data stack.
stack, return
A last in, first out list which contains the machine addresses of word definitions whose execution has not been completed by the address interpreter. As a word definition passes control to another definition, the return point is placed on the return stack.
The return stack may cautiously be used for other values, such as loop control parameters, and for pointers for interpretation of text.
string
A sequence of 8-bit bytes containing ASCII characters, located in memory by an initial byte address and byte count.
T
transportability
This term indicates that equivalent execution results when a program is executed on other than the system on which it was created. See 'equivalent execution'.
true
A non-zero value represents the true condition flag. Any non- zero value will be accepted by a standard word as 'true'; all standard words return one when leaving a ' true' flag.
Q
R
S
T
U
user area
An area in memory which contains the storage for user variables.
variables, user
So that the words of the FORTH vocabulary may be re-entrant (to different users), a copy of each system variable is maintained in the user area.
V
vocabulary
An ordered list of word definitions. Vocabulary lists are an advantage in reducing dictionary search time and in separating different word definitions that may carry the sane name.
W
word
A sequence of characters terminated by at least one blank (or 'return'). Words are usually obtained via the input stream, from a terminal or mass storage device.
word definition
A named FORTH execution procedure compiled into the dictionary. Its execution may be defined in terms of machine code, as a sequence of compilation addresses or other compiled words. If named, it nay be located by specifying this name and the vocabulary in which it is located.
word name
The name of a word definition. Standard names must be distinguished by their length and first thirty-one characters, and may not contain an ASCII null, blank, or 'return'.
word set
A group of FORTH word definitions listed by common characteristics. The standard word sets consist of:
Required Word Set
Nucleus Words
Interpreter Words
Compiler Words
Device Words
Extension Word Sets
32-bit Word Set
Assembler Ward Set
Included as reference material only: Reference Word Set
word set, compiler
Words which add new procedures to the dictionary or aid compilation by adding compilation addresses or data structures to the dictionary.
word set, devices
Words which allow access to mass storage and computer peripheral devices.
word set, interpreter
Words which support interpretation of text input from a terminal or mass storage by execution of corresponding dictionary entries, vocabularies, and terminal output.
word set, nucleus
The FORTH words generally defined in machine code that create the stacks and fundamental stack operators (virtual FORTH machine).
word set, reference
This set of words is provided as a reference document only, as a set of formerly standardized words and candidate words for standardization.
word set, required
The minimum words needed to compile and execute all Standard Programs.
word, standard
A named FORTH procedure definition, formally reviewed and accepted by the Standards Team. A serial number identifier {100..999} indicates a Standard Word. A functional alteration of a Standard Word will require assignment of a new serial number identifier.
The serial number identifier has no required use, other than to correlate the definition name with its unique Standard definition.
