7 The optional Block word set
7.1 Introduction
7.2 Additional terms
- block:
-
1024 characters of data on mass storage,
designated by a block number.
- block buffer:
-
A block-sized region of data space where a block is made
temporarily available for use. The current block buffer
is the block buffer most recently accessed by
BLOCK, BUFFER, LOAD, LIST, or
THRU.
7.3 Additional usage requirements
7.3.1 Data space
A program may access memory within a valid block buffer.
See:
3.3.3 Data space.
7.3.2 Block buffer regions
The address of a block buffer returned by
BLOCK or
BUFFER is transient. A call to
BLOCK or
BUFFER
may render a previously-obtained block-buffer address invalid, as
may a call to any word that:
- parses:
- displays characters on the user output device, such as
TYPE or EMIT;
- controls the user output device, such as CR or
AT-XY;
- receives or tests for the presence of characters from the
user input device such as ACCEPT or
KEY;
- waits for a condition or event, such as MS
or EKEY;
- manages the block buffers, such as FLUSH,
SAVE-BUFFERS, or EMPTY-BUFFERS;
- performs any operation on a file or file-name directory
that implies I/O, such as REFILL or any word that
returns an ior;
- implicitly performs I/O, such as text interpreter nesting
and un-nesting when files are being used (including un-nesting
implied by THROW).
If the input source is a block, these restrictions also apply to
the address returned by
SOURCE. Block buffers are
uniquely assigned to blocks.
See
A.7.3.2 Block buffer regions.
7.3.3 Parsing
The Block word set implements an alternative input source for the
text interpreter. When the input source is a block,
BLK shall
contain the non-zero block number and the input buffer is the
1024-character buffer containing that block.
A block is conventionally displayed as 16 lines of 64 characters.
A program may switch the input source to a block by using
LOAD or
THRU. Input sources may be nested using
LOAD and
EVALUATE in any order.
A program may reposition the parse area within a block by
manipulating
>IN. More extensive repositioning can be
accomplished using
SAVE-INPUT and
RESTORE-INPUT.
See:
3.4.1 Parsing.
7.3.4 Possible action on an ambiguous condition
See:
3.4.4 Possible actions on an ambiguous condition.
- A system with the Block word set may set interpretation state
and interpret a block.
7.4 Additional documentation requirements
7.4.1 System documentation
7.4.1.1 Implementation-defined options
7.4.1.2 Ambiguous conditions
7.4.1.3 Other system documentation
- any restrictions a multiprogramming system places on the use
of buffer addresses;
- the number of blocks available for source text and data.
7.4.2 Program documentation
- the number of blocks required by the program.
7.5 Compliance and labeling
7.5.1 Forth-2012 systems
The phrase "Providing the Block word set" shall be appended to
the label of any Standard System that provides all of the Block
word set.
The phrase "Providing
name(s) from the Block Extensions
word set" shall be appended to the label of any Standard System
that provides portions of the Block Extensions word set.
The phrase "Providing the Block Extensions word set" shall be
appended to the label of any Standard System that provides all of
the Block and Block Extensions word sets.
7.5.2 Forth-2012 programs
The phrase "Requiring the Block word set" shall be appended to
the label of Standard Programs that require the system to provide
the Block word set.
The phrase "Requiring
name(s) from the Block Extensions
word set" shall be appended to the label of Standard Programs
that require the system to provide portions of the Block Extensions
word set.
The phrase "Requiring the Block Extensions word set" shall be
appended to the label of Standard Programs that require the system
to provide all of the Block and Block Extensions word sets.
7.6 Glossary
7.6.1 Block words
7.6.2 Block extension words