597 lines
22 KiB
Plaintext
597 lines
22 KiB
Plaintext
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5. DEFINITIONS OF TERMS
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5. DEFINITIONS OF TERMS
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These are the definitions of the terms used within this Standard.
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address, byte
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An unsigned 16-bit number that locates an 8-bit byte in a
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standard FORTH address space over the range {0..65,535}. It
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may be a native machine address or a representation on a
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virtual machine, locating the addr-th byte within the
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virtual byte address space. Addresses are treated as
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unsigned numbers. See: "arithmetic, two's complement"
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address, compilation
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The numerical value compiled for a FORTH word definition
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which identifies that definition. The address interpreter
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uses this value to locate the machine code corresponding to
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each definition.
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address, native machine
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The natural address representation of the host computer.
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address, parameter field
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The address of the first byte of memory associated with a
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word definition for the storage of compilation addresses (in
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a colon definition), numeric data, text characters, etc.
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arithmetic, two's complement
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Arithmetic is performed using two's complement integers
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within a field of either 16 or 32 bits as indicated by the
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operation. Addition and subtraction of two's complement
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integers ignore any overflow condition. This allows numbers
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treated as unsigned to produce the same results as if the
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numbers had been treated as signed.
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block
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The 1024 bytes of data from mass storage which are
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referenced by block numbers in the range {0..the number of
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blocks available -1}. The actual amount of data transferred
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and the translation from block number to device and physical
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record is a function of the implementation. See: "block
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buffer" "mass storage"
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block buffer
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A 1024-byte memory area where a block is made temporarily
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available for use. Block buffers are uniquely assigned to
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blocks. See: "9.7 Multiprogramming Impact"
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byte
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An assembly of 8 bits. In reference to memory, it is the
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storage capacity for 8 bits.
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4
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5. DEFINITIONS OF TERMS
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character
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A 7-bit number the significance of which is given by the
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ASCII standard. When contained in a larger field, the
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higher order bits are zero. See: "6. REFERENCES"
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compilation
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The action of converting text words from the input stream
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into an internal form suitable for later execution. When in
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the compile state, the compilation addresses of FORTH words
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are compiled into the dictionary for later execution by the
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address interpreter. Numbers are compiled to be placed on
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the data stack when later executed. Numbers are accepted
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from the input stream unsigned or negatively signed and
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converted using the value of BASE . See: "number" "number
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conversion" "interpreter, text"
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defining word
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A word that, when executed, creates a new dictionary entry
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in the compilation vocabulary. The new word name is taken
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from the input stream. If the input stream is exhausted
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before the new name is available, an error condition exists.
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Example of defining words are: : CONSTANT CREATE
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definition
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See: "word definition"
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dictionary
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A structure of word definitions in computer memory which is
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extensible and grows toward higher memory addresses.
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Entries are organized in vocabularies to aid location by
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name. See: "search order"
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display
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The process of sending one or more characters to the current
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output device. These characters are typically displayed or
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printed on a terminal. The selection of the current output
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device is system dependent.
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division, floored
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Integer division in which the remainder carries the sign of
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the divisor or is zero, and the quotient is rounded to its
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arithmetic floor. Note that, except for error conditions,
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n1 n2 SWAP OVER /MOD ROT * + is identical to n1. See:
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"floor, arithmetic"
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Examples:
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dividend divisor remainder quotient
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10 7 3 1
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-10 7 4 -2
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10 -7 -4 -2
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-10 -7 -3 1
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equivalent execution
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5
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5. DEFINITIONS OF TERMS
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A standard program will produce the same results, exclusive
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of timing dependencies, when given the same inputs on any
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Standard System which has sufficient resources to execute
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the program. Only standard source programs are
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transportable.
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error condition
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An exceptional condition which requires action by the system
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which may be other than the expected function. Refer to the
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section "10. Error Conditions".
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false
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A zero number represents the false state of a flag.
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flag
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A number that may have one of two logical states, false or
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true. See: "false" "true"
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floor, arithmetic
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If z is any real number, then the floor of z is the greatest
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integer less than or equal to z.
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The floor of +.6 is 0
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The floor of -.4 is -1
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free field format
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Numbers are converted using the value of BASE and then
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displayed with no leading zeros. A trailing space is
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displayed. The number of characters displayed is the
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minimum number of characters, at least one, to uniquely
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represent the number. See: "number conversion"
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glossary
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A set of explanations in natural language to describe the
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corresponding computer execution of word definitions.
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immediate word
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A word which executes when encountered during compilation or
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interpretation. Immediate words handle special cases during
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compilation. See, for example, IF LITERAL ." etc.
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input stream
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A sequence of characters available to the system, for
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processing by the text interpreter. The input stream
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conventionally may be taken from the current input device
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(via the text input buffer) and mass storage (via a block
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buffer). BLK , >IN , TIB and #TIB specify the input stream.
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Words using or altering BLK , >IN , TIB and #TIB are
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responsible for maintaining and restoring control of the
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input stream.
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6
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5. DEFINITIONS OF TERMS
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The input stream extends from the offset value of >IN to the
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size of the input stream. If BLK is zero the input stream
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is contained within the area addressed by TIB and is #TIB
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bytes long. If BLK is non-zero the input stream is
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contained within the block buffer specified by BLK and is
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1024 bytes long. See: "11.8 Input Text"
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interpreter, address
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The machine code instructions, routine or other facilities
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that execute compiled word definitions containing
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compilation addresses.
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interpreter, text
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The word definitions(s) that repeatedly accepts a word name
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from the input stream, locates the corresponding compilation
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address and starts the address interpreter to execute it.
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Text from the input stream interpreted as a number leaves
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the corresponding value on the data stack. Numbers are
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accepted from the input stream unsigned or negatively signed
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and converted using the value of BASE . See: "number"
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"number conversion"
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layers
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The grouping of word names of each Standard word set to show
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like characteristics. No implementation requirements are
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implied by this grouping.
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layer, compiler
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Word definitions which add new procedures to the dictionary
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or which aid compilation by adding compilation addresses or
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data structures to the dictionary.
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layer, devices
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Word definitions which allow access to mass storage and
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computer peripheral devices.
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layer, interpreter
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Word definitions which support vocabularies, terminal
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output, and the interpretation of text from the text input
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buffer or a mass storage device by executing the
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corresponding word definitions.
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layer, nucleus
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Word definitions generally defined in machine code that
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control the execution of the fundamental operations of a
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virtual FORTH machine. This includes the address
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interpreter.
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load
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Redirection of the text interpreter's input stream to be
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from mass storage. This is the general method for
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compilation of new definitions into the dictionary.
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mass storage
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7
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5. DEFINITIONS OF TERMS
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Storage which might reside outside FORTH's address space.
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Mass storage data is made available in the form of 1024-byte
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blocks. A block is accessible within the FORTH address
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space in a block buffer. When a block has been indicated as
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UPDATEed (modified) the block will ultimately be transferred
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to mass storage.
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number
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When values exist within a larger field, the most-
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significant bits are zero. 16-bit numbers are represented
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in memory by addressing the first of two bytes at
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consecutive addresses. The byte order is unspecified by
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this Standard. Double numbers are represented on the stack
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with the most-significant 16 bits (with sign) most
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accessible. Double numbers are represented in memory by two
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consecutive 16-bit numbers. The address of the least
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significant 16 bits is two greater than the address of the
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most significant 16 bits. The byte order within each 16-bit
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field is unspecified. See: "arithmetic, two's complement"
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"number types" "9.8 Numbers" "11.7 Stack Parameters"
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number conversion
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Numbers are maintained internally in binary and represented
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externally by using graphic characters within the ASCII
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character set. Conversion between the internal and external
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forms is performed using the current value of BASE to
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determine the digits of a number. A digit has a value
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ranging from zero to the value of BASE-1. The digit with
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the value zero is represented by the ASCII character "0"
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(position 3/0 with the decimal equivalent of 48). This
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representation of digits proceeds through the ASCII
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character set to the character "(" corresponding to the
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decimal value 9. For digits with a value exceeding 9, the
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ASCII graphic characters beginning with the character "A"
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(position 4/1 with the decimal equivalent 65) corresponding
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to the decimal value 10 are used. This sequence then
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continues up to and including the digit with the decimal
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value 71 which is represented by the ASCII character "~"
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(position 7/14 with a decimal equivalent 126). A negative
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number may be represented by preceding the digits with a
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single leading minus sign, the character "-".
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number types
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All number types consist of some number of bits. These bits
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are either arbitrary or are weighted.
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8
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5. DEFINITIONS OF TERMS
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Signed and unsigned numbers use weighted bits. Weighted
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bits within a number have a value of a power of two
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beginning with the rightmost (least-significant) bit having
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the value of two to the zero power. This weighting
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continues to the leftmost bit increasing the power by one
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for each bit. For an unsigned number this weighting pattern
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includes the leftmost bit; thus, for an unsigned 16-bit
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number the weight of the leftmost bit is 32,768. For a
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signed number this weighting pattern includes the leftmost
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bit but the weight of the leftmost bit is negated; thus, for
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a signed 16-bit number the weight of the leftmost bit is
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-32,768. This weighting pattern for signed numbers is
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called two's complement notation.
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Unspecified weighted numbers are either unsigned numbers or
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signed numbers; program context determines whether the
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number is signed or unsigned. See: "11.7 Stack Parameters"
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pictured numeric output
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The use of numeric output definitions which convert
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numerical values into text strings. These definitions are
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used in a sequence which resembles a symbolic 'picture' of
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the desired text format. Conversion proceeds from least-
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significant digit to most-significant digit, and converted
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characters are stored from higher memory addresses to lower.
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program
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A complete specification of execution to achieve a specific
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function (application task) expressed in FORTH source code
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form.
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receive
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The process of obtaining one character from the current
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input device. The selection of the current input device is
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system dependent.
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recursion
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The process of self-reference, either directly or
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indirectly.
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return
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The means of indicating the end of text by striking a key on
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an input device. The key used is system dependent. This
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key is typically called "RETURN", "CARRIAGE RETURN", or
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"ENTER".
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screen
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Textual data arranged for editing. By convention, a screen
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consists of 16 lines (numbered 0 through 15) of 64
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characters each. Screens usually contain program source
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text, but may be used to view mass storage data. The first
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byte of a screen occupies the first byte of a mass storage
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block, which is the beginning point for text interpretation
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during a load.
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9
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5. DEFINITIONS OF TERMS
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search order
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A specification of the order in which selected vocabularies
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in the dictionary are searched. Execution of a vocabulary
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makes it the first vocabulary in the search order. The
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dictionary is searched whenever a word is to be located by
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its name. This order applies to all dictionary searches
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unless otherwise noted. The search order begins with the
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last vocabulary executed and ends with FORTH , unless
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altered in a system dependent manner.
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source definition
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Text consisting of word names suitable for compilation or
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execution by the text interpreter. Such text is usually
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arranged in screens and maintained on a mass storage device.
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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 alone, it implies the data
|
||
|
|
stack.
|
||
|
|
|
||
|
|
stack, return
|
||
|
|
A last in, first out list which contains the 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.
|
||
|
|
|
||
|
|
string, counted
|
||
|
|
A sequence of consecutive 8-bit bytes located in memory by
|
||
|
|
their low memory address. The byte at this address contains
|
||
|
|
a count {0..255} of the number of bytes following which are
|
||
|
|
part of the string. The count does not include the count
|
||
|
|
byte itself. Counted strings usually contain ASCII
|
||
|
|
characters.
|
||
|
|
|
||
|
|
string, text
|
||
|
|
A sequence of consecutive 8-bit bytes located in memory by
|
||
|
|
their low memory address and length in bytes. Strings
|
||
|
|
usually, but not exclusively, contain ASCII characters.
|
||
|
|
When the term 'string' is used alone or in conjunction with
|
||
|
|
other words it refers to text strings.
|
||
|
|
|
||
|
|
structure, control
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
10
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
5. DEFINITIONS OF TERMS
|
||
|
|
|
||
|
|
|
||
|
|
A group of FORTH words which when executed alter the
|
||
|
|
execution sequence. The group starts and terminates with
|
||
|
|
compiler words. Examples of control structures: DO ...
|
||
|
|
LOOP DO ... +LOOP BEGIN ... WHILE ... REPEAT BEGIN ...
|
||
|
|
UNTIL IF ... THEN IF ... ELSE ... THEN See: "9.9 Control
|
||
|
|
Structures"
|
||
|
|
|
||
|
|
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 state of a flag. Any
|
||
|
|
non-zero value will be accepted by a standard word as
|
||
|
|
'true'; all standard words return a 16-bit value with all
|
||
|
|
bits set to one when returning a 'true' flag.
|
||
|
|
|
||
|
|
user area
|
||
|
|
An area in memory which contains the storage for user
|
||
|
|
variable.
|
||
|
|
|
||
|
|
variable, user
|
||
|
|
A variable whose data storage area is usually located in the
|
||
|
|
user area. Some system variables are maintained in the user
|
||
|
|
area so that the words may be re-entrant to different users.
|
||
|
|
|
||
|
|
vocabulary
|
||
|
|
An ordered list of word definitions. Vocabularies are an
|
||
|
|
advantage in separating different word definitions that may
|
||
|
|
have the same name. More than one definition with the same
|
||
|
|
name can exist in one vocabulary. The latter is called a
|
||
|
|
redefinition. The most recently created redefinition will
|
||
|
|
be found when the vocabulary is searched.
|
||
|
|
|
||
|
|
vocabulary, compilation
|
||
|
|
The vocabulary into which new word definitions are appended.
|
||
|
|
|
||
|
|
word
|
||
|
|
A sequence of characters terminated by one blank or the end
|
||
|
|
of the input stream. Leading blanks are ignored. Words are
|
||
|
|
usually obtained via the input stream.
|
||
|
|
|
||
|
|
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 address, or other
|
||
|
|
compiled words.
|
||
|
|
|
||
|
|
word name
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
11
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
5. DEFINITIONS OF TERMS
|
||
|
|
|
||
|
|
|
||
|
|
The name of a word definition. Word names are limited to 31
|
||
|
|
characters and may not contain an ASCII space. If two
|
||
|
|
definitions have different word names in the same vocabulary
|
||
|
|
they must be uniquely findable when this vocabulary is
|
||
|
|
searched. See: "vocabulary" "9.5.3 EXPECT"
|
||
|
|
|
||
|
|
word set
|
||
|
|
A named group of FORTH word definitions in the Standard.
|
||
|
|
|
||
|
|
word set, assembler extension
|
||
|
|
Additional words which facilitate programming in the native
|
||
|
|
machine language of the computer which are by nature system
|
||
|
|
dependent.
|
||
|
|
|
||
|
|
word set, double number extension
|
||
|
|
Additional words which facilitate manipulation of 32-bit
|
||
|
|
numbers.
|
||
|
|
|
||
|
|
word set, required
|
||
|
|
The minimum words needed to compile and execute Standard
|
||
|
|
Programs.
|
||
|
|
|
||
|
|
word set, system extension
|
||
|
|
Additional words which facilitate the access to internal
|
||
|
|
system characteristics.
|
||
|
|
|
||
|
|
word, standard
|
||
|
|
A named FORTH procedure definition, in the Required word set
|
||
|
|
or any extension word sets, formally reviewed and accepted
|
||
|
|
by the Standards Team.
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
12
|
||
|
|
|