[gforth] / gforth / Attic / gforth.ds  

gforth: gforth/Attic/gforth.ds

Diff for /gforth/Attic/gforth.ds between version 1.13 and 1.14

version 1.13, Mon Mar 20 18:16:24 1995 UTC version 1.14, Thu Apr 20 09:42:52 1995 UTC
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 @table @var  @table @var
 @item word  @item word
 The name of the word. BTW, GNU Forth is case insensitive, so you can  The name of the word. BTW, GNU Forth is case insensitive, so you can
 type the words in in lower case.  type the words in in lower case (However, @pxref{core-idef}).
   
 @item Stack effect  @item Stack effect
 The stack effect is written in the notation @code{@var{before} --  The stack effect is written in the notation @code{@var{before} --
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 @node Defining Words, Wordlists, Locals, Words  @node Defining Words, Wordlists, Locals, Words
 @section Defining Words  @section Defining Words
   
   @menu
   * Values::
   @end menu
   
 @node Values,  , Defining Words, Defining Words  @node Values,  , Defining Words, Defining Words
 @subsection Values  @subsection Values
   
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 doc-does-handler!  doc-does-handler!
 doc-/does-handler  doc-/does-handler
   
   
   
 @node ANS conformance, Model, Words, Top  @node ANS conformance, Model, Words, Top
 @chapter ANS conformance  @chapter ANS conformance
   
   ANS Forth systems are required to document certain implementation
   choices. This chapter tries to meet these requirements. In many cases it
   gives a way to ask the system for the information instead of providing
   the information directly, in particular, if the information depends on
   the processor, the operating system or the installation options chosen,
   or if they are likely to change during the maintenance of gforth.
   
   @comment The framework for the rest has been taken from pfe.
   
   @menu
   * The Core Words::
   * The optional Block word set::
   * The optional Double Number word set::
   * The optional Exception word set::
   * The optional Facility word set::
   * The optional File-Access word set::
   * The optional Floating-Point word set::
   * The optional Locals word set::
   * The optional Memory-Allocation word set::
   * The optional Programming-Tools word set::
   * The optional Search-Order word set::
   * The optional String word set::
   @end menu
   
   
   @c =====================================================================
   @node The Core Words, The optional Block word set, ANS conformance, ANS conformance
   @comment  node-name,  next,  previous,  up
   @section The Core Words
   @c =====================================================================
   
   @menu
   * core-idef::
   * core-ambcond::
   * core-other::
   @end menu
   
   @c ---------------------------------------------------------------------
   @node core-idef, core-ambcond, The Core Words, The Core Words
   @comment  node-name,  next,  previous,  up
   @subsection Implementation Defined Options
   @c ---------------------------------------------------------------------
   
   @table @i
   
   @item (Cell) aligned addresses:
   processor-dependent. Gforths alignment words perform natural alignment
   (e.g., an address aligned for a datum of size 8 is divisible by
   8). Unaligned accesses usually result in a @code{-23 THROW}.
   
   @item @code{EMIT} and non-graphic characters:
   The character is output using the C library function (actually, macro)
   @code{putchar}.
   
   @item character editing of @code{ACCEPT} and @code{EXPECT}:
   This is modeled on the GNU readline library (@pxref{Readline
   Interaction, , Command Line Editing, readline, The GNU Readline
   Library}) with Emacs-like key bindings. @kbd{Tab} deviates a little by
   producing a full word completion every time you type it (instead of
   producing the common prefix of all completions).
   
   @item character set:
   The character set of your computer and display device. Gforth is
   8-bit-clean (but some other component in your system may make trouble).
   
   @item Character-aligned address requirements:
   installation-dependent. Currently a character is represented by a C
   @code{unsigned char}; in the future we might switch to @code{wchar_t}
   (Comments on that requested).
   
   @item character-set extensions and matching of names:
   Any character except 0 can be used in a name. Matching is
   case-insensitive. The matching is performed using the C function
   @code{strncasecmp}, whose function is probably influenced by the
   locale. E.g., the @code{C} locale does not know about accents and
   umlauts, so they are matched case-sensitively in that locale. For
   portability reasons it is best to write programs such that they work in
   the @code{C} locale. Then one can use libraries written by a Polish
   programmer (who might use words containing ISO Latin-2 encoded
   characters) and by a French programmer (ISO Latin-1) in the same program
   (of course, @code{WORDS} will produce funny results for some of the
   words (which ones, depends on the font you are using)). Also, the locale
   you prefer may not be available in other operating systems. Hopefully,
   Unicode will solve these problems one day.
   
   @item conditions under which control characters match a space delimiter:
   If @code{WORD} is called with the space character as a delimiter, all
   white-space characters (as identified by the C macro @code{isspace()})
   are delimiters. @code{PARSE}, on the other hand, treats space like other
   delimiters. @code{PARSE-WORD} treats space like @code{WORD}, but behaves
   like @code{PARSE} otherwise. @code{(NAME)}, which is used by the outer
   interpreter (aka text interpreter) by default, treats all white-space
   characters as delimiters.
   
   @item format of the control flow stack:
   The data stack is used as control flow stack. The size of a control flow
   stack item in cells is given by the constant @code{cs-item-size}. At the
   time of this writing, an item consists of a (pointer to a) locals list
   (third), an address in the code (second), and a tag for identifying the
   item (TOS). The following tags are used: @code{defstart},
   @code{live-orig}, @code{dead-orig}, @code{dest}, @code{do-dest},
   @code{scopestart}.
   
   @item conversion of digits > 35
   The characters @code{[\]^_'} are the digits with the decimal value
   36@minus{}41. There is no way to input many of the larger digits.
   
   @item display after input terminates in @code{ACCEPT} and @code{EXPECT}:
   The cursor is moved to the end of the entered string. If the input is
   terminated using the @kbd{Return} key, a space is typed.
   
   @item exception abort sequence of @code{ABORT"}:
   The error string is stored into the variable @code{"error} and a
   @code{-2 throw} is performed.
   
   @item input line terminator:
   For interactive input, @kbd{C-m} and @kbd{C-j} terminate lines. One of
   these characters is typically produced when you type the @kbd{Enter} or
   @kbd{Return} key.
   
   @item maximum size of a counted string:
   @code{s" /counted-string" environment? drop .}. Currently 255 characters
   on all ports, but this may change.
   
   @item maximum size of a parsed string:
   Given by the constant @code{/line}. Currently 255 characters.
   
   @item maximum size of a definition name, in characters:
   31
   
   @item maximum string length for @code{ENVIRONMENT?}, in characters:
   31
   
   @item method of selecting the user input device:
   The user input device is the standard input. There is current no way to
   change it from within gforth. However, the input can typically be
   redirected in the command line that starts gforth.
   
   @item method of selecting the user output device:
   The user output device is the standard output. It cannot be redirected
   from within gforth, but typically from the command line that starts
   gforth. Gforth uses buffered output, so output on a terminal does not
   become visible before the next newline or buffer overflow. Output on
   non-terminals is invisible until the buffer overflows.
   
   @item methods of dictionary compilation:
   Waht are we expected to document here?
   
   @item number of bits in one address unit:
   @code{s" address-units-bits" environment? drop .}. 8 in all current
   ports.
   
   @item number representation and arithmetic:
   Processor-dependent. Binary two's complement on all current ports.
   
   @item ranges for integer types:
   Installation-dependent. Make environmental queries for @code{MAX-N},
   @code{MAX-U}, @code{MAX-D} and @code{MAX-UD}. The lower bounds for
   unsigned (and positive) types is 0. The lower bound for signed types on
   two's complement and one's complement machines machines can be computed
   by adding 1 to the upper bound.
   
   @item read-only data space regions:
   The whole Forth data space is writable.
   
   @item size of buffer at @code{WORD}:
   @code{PAD HERE - .}. 104 characters on 32-bit machines. The buffer is
   shared with the pictured numeric output string. If overwriting
   @code{PAD} is acceptable, it is as large as the remaining dictionary
   space, although only as much can be sensibly used as fits in a counted
   string.
   
   @item size of one cell in address units:
   @code{1 cells .}.
   
   @item size of one character in address units:
   @code{1 chars .}. 1 on all current ports.
   
   @item size of the keyboard terminal buffer:
   Varies. You can determine the size at a specific time using @code{lp@
   tib - .}. It is shared with the locals stack and TIBs of files that
   include the current file. You can change the amount of space for TIBs
   and locals stack at gforth startup with the command line option
   @code{-l}.
   
   @item size of the pictured numeric output buffer:
   @code{PAD HERE - .}. 104 characters on 32-bit machines. The buffer is
   shared with @code{WORD}.
   
   @item size of the scratch area returned by @code{PAD}:
   The remainder of dictionary space. You can even use the unused part of
   the data stack space. The current size can be computed with @code{sp@
   pad - .}.
   
   @item system case-sensitivity characteristics:
   Dictionary searches are case insensitive. However, as explained above
   under @i{character-set extensions}, the matching for non-ASCII
   characters is determined by the locale you are using. In the default
   @code{C} locale all non-ASCII characters are matched case-sensitively.
   
   @item system prompt:
   @code{ ok} in interpret state, @code{ compiled} in compile state.
   
   @item division rounding:
   installation dependent. @code{s" floored" environment? drop .}. We leave
   the choice to gcc (what to use for @code{/}) and to you (whether to use
   @code{fm/mod}, @code{sm/rem} or simply @code{/}).
   
   @item values of @code{STATE} when true:
   -1.
   
   @item values returned after arithmetic overflow:
   On two's complement machines, arithmetic is performed modulo
   2**bits-per-cell for single arithmetic and 4**bits-per-cell for double
   arithmetic (with appropriate mapping for signed types). Division by zero
   typically results in a @code{-55 throw} (floatingpoint unidentified
   fault), although a @code{-10 throw} (divide by zero) would be more
   appropriate.
   
   @item whether the current definition can be found after @t{DOES>}:
   No.
   
   @end table
   
   @c ---------------------------------------------------------------------
   @node core-ambcond, core-other, core-idef, The Core Words
   @comment  node-name,  next,  previous,  up
   @subsection Ambiguous conditions
   @c ---------------------------------------------------------------------
   
   @table @i
   
   @item a name is neither a word nor a number:
   @code{-13 throw} (Undefined word)
   
   @item a definition name exceeds the maximum length allowed:
   @code{-19 throw} (Word name too long)
   
   @item addressing a region not inside the various data spaces of the forth system:
   The stacks, code space and name space are accessible. Machine code space is
   typically readable. Accessing other addresses gives results dependent on
   the operating system. On decent systems: @code{-9 throw} (Invalid memory
   address).
   
   @item argument type incompatible with parameter:
   This is usually not caught. Some words perform checks, e.g., the control
   flow words, and issue a @code{ABORT"} or @code{-12 THROW} (Argument type
   mismatch).
   
   @item attempting to obtain the execution token of a word with undefined execution semantics:
   You get an execution token representing the compilation semantics
   instead.
   
   @item dividing by zero:
   typically results in a @code{-55 throw} (floating point unidentified
   fault), although a @code{-10 throw} (divide by zero) would be more
   appropriate.
   
   @item insufficient data stack or return stack space:
   Not checked. This typically results in mysterious illegal memory
   accesses, producing @code{-9 throw} (Invalid memory address) or
   @code{-23 throw} (Address alignment exception).
   
   @item insufficient space for loop control parameters:
   like other return stack overflows.
   
   @item insufficient space in the dictionary:
   Not checked. Similar results as stack overflows. However, typically the
   error appears at a different place when one inserts or removes code.
   
   @item interpreting a word with undefined interpretation semantics:
   For some words, we defined interpretation semantics. For the others:
   @code{-14 throw} (Interpreting a compile-only word). Note that this is
   checked only by the outer (aka text) interpreter; if the word is
   @code{execute}d in some other way, it will typically perform it's
   compilation semantics even in interpret state. (We could change @code{'}
   and relatives not to give the xt of such words, but we think that would
   be too restrictive).
   
   @item modifying the contents of the input buffer or a string literal:
   These are located in writable memory and can be modified.
   
   @item overflow of the pictured numeric output string:
   Not checked.
   
   @item parsed string overflow:
   @code{PARSE} cannot overflow. @code{WORD} does not check for overflow.
   
   @item producing a result out of range:
   On two's complement machines, arithmetic is performed modulo
   2**bits-per-cell for single arithmetic and 4**bits-per-cell for double
   arithmetic (with appropriate mapping for signed types). Division by zero
   typically results in a @code{-55 throw} (floatingpoint unidentified
   fault), although a @code{-10 throw} (divide by zero) would be more
   appropriate. @code{convert} and @code{>number} currently overflow
   silently.
   
   @item reading from an empty data or return stack:
   The data stack is checked by the outer (aka text) interpreter after
   every word executed. If it has underflowed, a @code{-4 throw} (Stack
   underflow) is performed. Apart from that, the stacks are not checked and
   underflows can result in similar behaviour as overflows (of adjacent
   stacks).
   
   @item unexepected end of the input buffer, resulting in an attempt to use a zero-length string as a name:
   @code{Create} and its descendants perform a @code{-16 throw} (Attempt to
   use zero-length string as a name). Words like @code{'} probably will not
   find what they search. Note that it is possible to create zero-length
   names with @code{nextname} (should it not?).
   
   @item @code{>IN} greater than input buffer:
   The next invocation of a parsing word returns a string wih length 0.
   
   @item @code{RECURSE} appears after @code{DOES>}:
   Compiles a recursive call to the defining word not to the defined word.
   
   @item argument input source different than current input source for @code{RESTORE-INPUT}:
   !!???If the argument input source is a valid input source then it gets
   restored. Otherwise causes @code{-12 THROW} which unless caught issues
   the message "argument type mismatch" and aborts.
   
   @item data space containing definitions gets de-allocated:
   Deallocation with @code{allot} is not checked. This typically resuls in
   memory access faults or execution of illegal instructions.
   
   @item data space read/write with incorrect alignment:
   Processor-dependent. Typically results in a @code{-23 throw} (Address
   alignment exception). Under Linux on a 486 or later processor with
   alignment turned on, incorrect alignment results in a @code{-9 throw}
   (Invalid memory address). There are reportedly some processors with
   alignment restrictions that do not report them.
   
   @item data space pointer not properly aligned, @code{,}, @code{C,}:
   Like other alignment errors.
   
   @item less than u+2 stack items (@code{PICK} and @code{ROLL}):
   Not checked. May cause an illegal memory access.
   
   @item loop control parameters not available:
   Not checked. The counted loop words simply assume that the top of return
   stack items are loop control parameters and behave accordingly.
   
   @item most recent definition does not have a name (@code{IMMEDIATE}):
   @code{abort" last word was headerless"}.
   
   @item name not defined by @code{VALUE} used by @code{TO}:
   @code{-32 throw} (Invalid name argument)
   
   @item name not found (@code{'}, @code{POSTPONE}, @code{[']}, @code{[COMPILE]}:
   @code{-13 throw} (Undefined word)
   
   @item parameters are not of the same type (@code{DO}, @code{?DO}, @code{WITHIN}):
   Gforth behaves as if they were of the same type. I.e., you can predict
   the behaviour by interpreting all parameters as, e.g., signed.
   
   @item @code{POSTPONE} or @code{[COMPILE]} applied to @code{TO}:
   Assume @code{: X POSTPONE TO ; IMMEDIATE}. @code{X} is equivalent to
   @code{TO}.
   
   @item String longer than a counted string returned by @code{WORD}:
   Not checked. The string will be ok, but the count will, of course,
   contain only the least significant bits of the length.
   
   @item u greater than or equal to the number of bits in a cell (@code{LSHIFT}, @code{RSHIFT}:
   Processor-dependent. Typical behaviours are returning 0 and using only
   the low bits of the shift count.
   
   @item word not defined via @code{CREATE}:
   @code{>BODY} produces the PFA of the word no matter how it was defined.
   
   @code{DOES>} changes the execution semantics of the last defined word no
   matter how it was defined. E.g., @code{CONSTANT DOES>} is equivalent to
   @code{CREATE , DOES>}.
   
   @item words improperly used outside @code{<#} and @code{#>}:
   Not checked. As usual, you can expect memory faults.
   
   @end table
   
   
   @c ---------------------------------------------------------------------
   @node core-other,  , core-ambcond, The Core Words
   @comment  node-name,  next,  previous,  up
   @subsection Other system documentation
   @c ---------------------------------------------------------------------
   
   @table @i
   
   @item nonstandard words using @code{PAD}:
   None.
   
   @item operator's terminal facilities available:
   !!??
   
   @item program data space available:
   @code{sp@ here - .} gives the space remaining for dictionary and data
   stack together.
   
   @item return stack space available:
   !!??
   
   @item stack space available:
   @code{sp@ here - .} gives the space remaining for dictionary and data
   stack together.
   
   @item system dictionary space required, in address units:
   Type @code{here forthstart - .} after startup. At the time of this
   writing, this gives 70108 (bytes) on a 32-bit system.
   @end table
   
   
   @c =====================================================================
   @node The optional Block word set, The optional Double Number word set, The Core Words, ANS conformance
   @comment  node-name,  next,  previous,  up
   @section The optional Block word set
   @c =====================================================================
   
   @menu
   * block-idef::
   * block-ambcond::
   * block-other::
   @end menu
   
   
   @c ---------------------------------------------------------------------
   @node block-idef, block-ambcond, The optional Block word set, The optional Block word set
   @comment  node-name,  next,  previous,  up
   @subsection Implementation Defined Options
   @c ---------------------------------------------------------------------
   
   @table @i
   
   @item the format for display by @code{LIST}:
   First the screen number is displayed, then 16 lines of 64 characters,
   each line preceded by the line number.
   
   @item the length of a line affected by @code{\}:
   64 characters.
   @end table
   
   
   @c ---------------------------------------------------------------------
   @node block-ambcond, block-other, block-idef, The optional Block word set
   @comment  node-name,  next,  previous,  up
   @subsection Ambiguous conditions
   @c ---------------------------------------------------------------------
   
   @table @i
   
   @item correct block read was not possible:
   Typically results in a @code{throw} of some OS-derived value (between
   -512 and -2048). If the blocks file was just not long enough, blanks are
   supplied for the missing portion.
   
   @item I/O exception in block transfer:
   Typically results in a @code{throw} of some OS-derived value (between
   -512 and -2048).
   
   @item invalid block number:
   @code{-35 throw} (Invalid block number)
   
   @item a program directly alters the contents of @code{BLK}:
   The input stream is switched to that other block, at the same
   position. If the storing to @code{BLK} happens when interpreting
   non-block input, the system will get quite confused when the block ends.
   
   @item no current block buffer for @code{UPDATE}:
   @code{UPDATE} has no effect.
   
   @end table
   
   
   @c ---------------------------------------------------------------------
   @node block-other,  , block-ambcond, The optional Block word set
   @comment  node-name,  next,  previous,  up
   @subsection Other system documentation
   @c ---------------------------------------------------------------------
   
   @table @i
   
   @item any restrictions a multiprogramming system places on the use of buffer addresses:
   No restrictions (yet).
   
   @item the number of blocks available for source and data:
   depends on your disk space.
   
   @end table
   
   
   @c =====================================================================
   @node The optional Double Number word set, The optional Exception word set, The optional Block word set, ANS conformance
   @comment  node-name,  next,  previous,  up
   @section The optional Double Number word set
   @c =====================================================================
   
   @menu
   * double-idef::
   * double-ambcond::
   * double-other::
   @end menu
   
   
   @c ---------------------------------------------------------------------
   @node double-idef, double-ambcond, The optional Double Number word set, The optional Double Number word set
   @comment  node-name,  next,  previous,  up
   @subsection Implementation Defined Options
   @c ---------------------------------------------------------------------
   
   No additional documentation requirements.
   
   
   @c ---------------------------------------------------------------------
   @node double-ambcond, double-other, double-idef, The optional Double Number word set
   @comment  node-name,  next,  previous,  up
   @subsection Ambiguous conditions
   @c ---------------------------------------------------------------------
   
   @table @i
   
   @item @var{d} outside of range on @var{n} in @code{D>S}:
   The least significant cell of @var{d} is produced.
   
   @end table
   
   
   @c ---------------------------------------------------------------------
   @node double-other,  , double-ambcond, The optional Double Number word set
   @comment  node-name,  next,  previous,  up
   @subsection Other system documentation
   @c ---------------------------------------------------------------------
   
   No additional documentation requirements.
   
   
   @c =====================================================================
   @node The optional Exception word set, The optional Facility word set, The optional Double Number word set, ANS conformance
   @comment  node-name,  next,  previous,  up
   @section The optional Exception word set
   @c =====================================================================
   
   @menu
   * exception-idef::
   * exception-ambcond::
   * exception-other::
   @end menu
   
   
   @c ---------------------------------------------------------------------
   @node exception-idef, exception-ambcond, The optional Exception word set, The optional Exception word set
   @comment  node-name,  next,  previous,  up
   @subsection Implementation Defined Options
   @c ---------------------------------------------------------------------
   
   @table @i
   @item @code{THROW}-codes used in the system:
   The codes -256@minus{}-511 are used for reporting signals (see
   @file{errore.fs}). The codes -512@minus{}-2047 are used for OS errors
   (for file and memory allocation operations). The mapping from OS error
   numbers to throw code is -512@minus{}@var{errno}. One side effect of
   this mapping is that undefined OS errors produce a message with a
   strange number; e.g., @code{-1000 THROW} results in @code{Unknown error
   488} on my system.
   @end table
   
   
   @c ---------------------------------------------------------------------
   @node exception-ambcond, exception-other, exception-idef, The optional Exception word set
   @comment  node-name,  next,  previous,  up
   @subsection Ambiguous conditions
   @c ---------------------------------------------------------------------
   
   No additional documentation requirements.
   
   
   @c ---------------------------------------------------------------------
   @node exception-other,  , exception-ambcond, The optional Exception word set
   @comment  node-name,  next,  previous,  up
   @subsection Other system documentation
   @c ---------------------------------------------------------------------
   
   No additional documentation requirements.
   
   
   @c =====================================================================
   @node The optional Facility word set, The optional File-Access word set, The optional Exception word set, ANS conformance
   @comment  node-name,  next,  previous,  up
   @section The optional Facility word set
   @c =====================================================================
   
   @menu
   * facility-idef::
   * facility-ambcond::
   * facility-other::
   @end menu
   
   
   @c ---------------------------------------------------------------------
   @node facility-idef, facility-ambcond, The optional Facility word set, The optional Facility word set
   @comment  node-name,  next,  previous,  up
   @subsection Implementation Defined Options
   @c ---------------------------------------------------------------------
   
   @table @i
   
   @item encoding of keyboard events (@code{EKEY}):
   Not yet implemeted.
   
   @item duration of a system clock tick
   System dependent. With respect to @code{MS}, the time is specified in
   microseconds. How well the OS and the hardware implement this, is
   another question.
   
   @item repeatability to be expected from the execution of @code{MS}:
   System dependent. On Unix, a lot depends on load. If the system is
   lightly loaded, and the delay is short enough that gforth does not get
   swapped out, the performance should be acceptable. Under MS-DOS and
   other single-tasking systems, it should be good.
   
   @end table
   
   
   @c ---------------------------------------------------------------------
   @node facility-ambcond, facility-other, facility-idef, The optional Facility word set
   @comment  node-name,  next,  previous,  up
   @subsection Ambiguous conditions
   @c ---------------------------------------------------------------------
   
   @table @i
   
   @item @code{AT-XY} can't be performed on user output device:
   Largely terminal dependant. No range checks are done on the arguments.
   No errors are reported. You may see some garbage appearing, you may see
   simply nothing happen.
   
   @end table
   
   
   @c ---------------------------------------------------------------------
   @node facility-other,  , facility-ambcond, The optional Facility word set
   @comment  node-name,  next,  previous,  up
   @subsection Other system documentation
   @c ---------------------------------------------------------------------
   
   No additional documentation requirements.
   
   
   @c =====================================================================
   @node The optional File-Access word set, The optional Floating-Point word set, The optional Facility word set, ANS conformance
   @comment  node-name,  next,  previous,  up
   @section The optional File-Access word set
   @c =====================================================================
   
   @menu
   * file-idef::
   * file-ambcond::
   * file-other::
   @end menu
   
   
   @c ---------------------------------------------------------------------
   @node file-idef, file-ambcond, The optional File-Access word set, The optional File-Access word set
   @comment  node-name,  next,  previous,  up
   @subsection Implementation Defined Options
   @c ---------------------------------------------------------------------
   
   @table @i
   
   @item File access methods used:
   @code{R/O}, @code{R/W} and @code{BIN} work as you would
   expect. @code{W/O} translates into the C file opening mode @code{w} (or
   @code{wb}): The file is cleared, if it exists, and created, if it does
   not (both with @code{open-file} and @code{create-file}.  Under Unix
   @code{create-file} creates a file with 666 permissions modified by your
   umask.
   
   @item file exceptions:
   The file words do not raise exceptions (except, perhaps, memory access
   faults when you pass illegal addresses or file-ids).
   
   @item file line terminator:
   System-dependent. Gforth uses C's newline character as line
   terminator. What the actual character code(s) of this are is
   system-dependent.
   
   @item file name format
   System dependent. Gforth just uses the file name format of your OS.
   
   @item information returned by @code{FILE-STATUS}:
   @code{FILE-STATUS} returns the most powerful file access mode allowed
   for the file: Either @code{R/O}, @code{W/O} or @code{R/W}. If the file
   cannot be accessed, @code{R/O BIN} is returned. @code{BIN} is applicable
   along with the retured mode.
   
   @item input file state after an exception when including source:
   All files that are left via the exception are closed.
   
   @item @var{ior} values and meaning:
   The @var{ior}s returned by the file words are intended as throw
   codes. They typically are in the range -512@minus{}-2047 of OS errors.
   The mapping from OS error numbers to @var{ior}s is
   -512@minus{}@var{errno}.
   
   @item maximum depth of file input nesting:
   limited by the amount of return stack, locals/TIB stack, and the number
   of open files available. This should not give you troubles.
   
   @item maximum size of input line:
   @code{/line}. Currently 255.
   
   @item methods of mapping block ranges to files:
   Currently, the block words automatically access the file
   @file{blocks.fb} in the currend working directory. More sophisticated
   methods could be implemented if there is demand (and a volunteer).
   
   @item number of string buffers provided by @code{S"}:
   1
   
   @item size of string buffer used by @code{S"}:
   @code{/line}. currently 255.
   
   @end table
   
   @c ---------------------------------------------------------------------
   @node file-ambcond, file-other, file-idef, The optional File-Access word set
   @comment  node-name,  next,  previous,  up
   @subsection Ambiguous conditions
   @c ---------------------------------------------------------------------
   
   @table @i
   
   @item attempting to position a file outside it's boundaries:
   @code{REPOSITION-FILE} is performed as usual: Afterwards,
   @code{FILE-POSITION} returns the value given to @code{REPOSITION-FILE}.
   
   @item attempting to read from file positions not yet written:
   End-of-file, i.e., zero characters are read and no error is reported.
   
   @item @var{file-id} is invalid (@code{INCLUDE-FILE}):
   An appropriate exception may be thrown, but a memory fault or other
   problem is more probable.
   
   @item I/O exception reading or closing @var{file-id} (@code{include-file}, @code{included}):
   The @var{ior} produced by the operation, that discovered the problem, is
   thrown.
   
   @item named file cannot be opened (@code{included}):
   The @var{ior} produced by @code{open-file} is thrown.
   
   @item requesting an unmapped block number:
   There are no unmapped legal block numbers. On some operating systems,
   writing a block with a large number may overflow the file system and
   have an error message as consequence.
   
   @item using @code{source-id} when @code{blk} is non-zero:
   @code{source-id} performs its function. Typically it will give the id of
   the source which loaded the block. (Better ideas?)
   
   @end table
   
   
   @c ---------------------------------------------------------------------
   @node file-other,  , file-ambcond, The optional File-Access word set
   @comment  node-name,  next,  previous,  up
   @subsection Other system documentation
   @c ---------------------------------------------------------------------
   
   @table @i
   
   @item
   
   @end table
   
   
   @c =====================================================================
   @node  The optional Floating-Point word set, The optional Locals word set, The optional File-Access word set, ANS conformance
   @comment  node-name,  next,  previous,  up
   @section
   @c =====================================================================
   
   @menu
   * floating-idef::               floating-ambcond:: floating-other::
   * floating-ambcond::
   * floating-other::
   @end menu
   
   
   @c ---------------------------------------------------------------------
   @node floating-idef, floating-ambcond, The optional Floating-Point word set, The optional Floating-Point word set
   @comment  node-name,  next,  previous,  up
   @subsection Implementation Defined Options
   @c ---------------------------------------------------------------------
   
   @table @i
   
   @item
   
   @end table
   
   
   @c ---------------------------------------------------------------------
   @node floating-ambcond, floating-other, floating-idef, The optional Floating-Point word set
   @comment  node-name,  next,  previous,  up
   @subsection Ambiguous conditions
   @c ---------------------------------------------------------------------
   
   @table @i
   
   @item
   
   @end table
   
   
   @c ---------------------------------------------------------------------
   @node floating-other,  , floating-ambcond, The optional Floating-Point word set
   @comment  node-name,  next,  previous,  up
   @subsection Other system documentation
   @c ---------------------------------------------------------------------
   
   @table @i
   
   @item
   
   @end table
   
   
   @c =====================================================================
   @node  The optional Locals word set, The optional Memory-Allocation word set, The optional Floating-Point word set, ANS conformance
   @comment  node-name,  next,  previous,  up
   @section
   @c =====================================================================
   
   @menu
   * locals-idef::
   * locals-ambcond::
   * locals-other::
   @end menu
   
   
   @c ---------------------------------------------------------------------
   @node locals-idef, locals-ambcond, The optional Locals word set, The optional Locals word set
   @comment  node-name,  next,  previous,  up
   @subsection Implementation Defined Options
   @c ---------------------------------------------------------------------
   
   @table @i
   
   @item
   
   @end table
   
   
   @c ---------------------------------------------------------------------
   @node locals-ambcond, locals-other, locals-idef, The optional Locals word set
   @comment  node-name,  next,  previous,  up
   @subsection Ambiguous conditions
   @c ---------------------------------------------------------------------
   
   @table @i
   
   @item
   
   @end table
   
   
   @c ---------------------------------------------------------------------
   @node locals-other,  , locals-ambcond, The optional Locals word set
   @comment  node-name,  next,  previous,  up
   @subsection Other system documentation
   @c ---------------------------------------------------------------------
   
   @table @i
   
   @item
   
   @end table
   
   
   @c =====================================================================
   @node  The optional Memory-Allocation word set, The optional Programming-Tools word set, The optional Locals word set, ANS conformance
   @comment  node-name,  next,  previous,  up
   @section
   @c =====================================================================
   
   @menu
   * memory-idef::
   * memory-ambcond::
   * memory-other::
   @end menu
   
   
   @c ---------------------------------------------------------------------
   @node memory-idef, memory-ambcond, The optional Memory-Allocation word set, The optional Memory-Allocation word set
   @comment  node-name,  next,  previous,  up
   @subsection Implementation Defined Options
   @c ---------------------------------------------------------------------
   
   @table @i
   
   @item
   
   @end table
   
   
   @c ---------------------------------------------------------------------
   @node memory-ambcond, memory-other, memory-idef, The optional Memory-Allocation word set
   @comment  node-name,  next,  previous,  up
   @subsection Ambiguous conditions
   @c ---------------------------------------------------------------------
   
   @table @i
   
   @item
   
   @end table
   
   
   @c ---------------------------------------------------------------------
   @node memory-other,  , memory-ambcond, The optional Memory-Allocation word set
   @comment  node-name,  next,  previous,  up
   @subsection Other system documentation
   @c ---------------------------------------------------------------------
   
   @table @i
   
   @item
   
   @end table
   
   
   @c =====================================================================
   @node  The optional Programming-Tools word set, The optional Search-Order word set, The optional Memory-Allocation word set, ANS conformance
   @comment  node-name,  next,  previous,  up
   @section
   @c =====================================================================
   
   @menu
   * programming-idef::
   * programming-ambcond::
   * programming-other::
   @end menu
   
   
   @c ---------------------------------------------------------------------
   @node programming-idef, programming-ambcond, The optional Programming-Tools word set, The optional Programming-Tools word set
   @comment  node-name,  next,  previous,  up
   @subsection Implementation Defined Options
   @c ---------------------------------------------------------------------
   
   @table @i
   
   @item
   
   @end table
   
   
   @c ---------------------------------------------------------------------
   @node programming-ambcond, programming-other, programming-idef, The optional Programming-Tools word set
   @comment  node-name,  next,  previous,  up
   @subsection Ambiguous conditions
   @c ---------------------------------------------------------------------
   
   @table @i
   
   @item
   
   @end table
   
   
   @c ---------------------------------------------------------------------
   @node programming-other,  , programming-ambcond, The optional Programming-Tools word set
   @comment  node-name,  next,  previous,  up
   @subsection Other system documentation
   @c ---------------------------------------------------------------------
   
   @table @i
   
   @item
   
   @end table
   
   
   @c =====================================================================
   @node  The optional Search-Order word set, The optional String word set, The optional Programming-Tools word set, ANS conformance
   @comment  node-name,  next,  previous,  up
   @section
   @c =====================================================================
   
   @menu
   * search-idef::
   * search-ambcond::
   * search-other::
   @end menu
   
   
   @c ---------------------------------------------------------------------
   @node search-idef, search-ambcond, The optional Search-Order word set, The optional Search-Order word set
   @comment  node-name,  next,  previous,  up
   @subsection Implementation Defined Options
   @c ---------------------------------------------------------------------
   
   @table @i
   
   @item
   
   @end table
   
   
   @c ---------------------------------------------------------------------
   @node search-ambcond, search-other, search-idef, The optional Search-Order word set
   @comment  node-name,  next,  previous,  up
   @subsection Ambiguous conditions
   @c ---------------------------------------------------------------------
   
   @table @i
   
   @item
   
   @end table
   
   
   @c ---------------------------------------------------------------------
   @node search-other,  , search-ambcond, The optional Search-Order word set
   @comment  node-name,  next,  previous,  up
   @subsection Other system documentation
   @c ---------------------------------------------------------------------
   
   @table @i
   
   @item
   
   @end table
   
   
   @c =====================================================================
   @node  The optional String word set,  , The optional Search-Order word set, ANS conformance
   @comment  node-name,  next,  previous,  up
   @section
   @c =====================================================================
   
   @menu
   * string-idef::
   * string-ambcond::
   * string-other::
   @end menu
   
   
   @c ---------------------------------------------------------------------
   @node string-idef, string-ambcond, The optional String word set, The optional String word set
   @comment  node-name,  next,  previous,  up
   @subsection Implementation Defined Options
   @c ---------------------------------------------------------------------
   
   @table @i
   
   @item
   
   @end table
   
   
   @c ---------------------------------------------------------------------
   @node string-ambcond, string-other, string-idef, The optional String word set
   @comment  node-name,  next,  previous,  up
   @subsection Ambiguous conditions
   @c ---------------------------------------------------------------------
   
   @table @i
   
   @item
   
   @end table
   
   
   @c ---------------------------------------------------------------------
   @node string-other,  , string-ambcond, The optional String word set
   @comment  node-name,  next,  previous,  up
   @subsection Other system documentation
   @c ---------------------------------------------------------------------
   
   @table @i
   
   @item
   
   @end table
   
   
   

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