[gforth] / gforth / Attic / gforth.ds  

gforth: gforth/Attic/gforth.ds

Diff for /gforth/Attic/gforth.ds between version 1.3 and 1.7

version 1.3, Wed Nov 23 16:54:39 1994 UTC version 1.7, Tue Jan 24 17:31:22 1995 UTC
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 \input texinfo   @c -*-texinfo-*-  \input texinfo   @c -*-texinfo-*-
 @comment The source is gforth.ds, from which gforth.texi is generated  @comment The source is gforth.ds, from which gforth.texi is generated
 @comment %**start of header (This is for running Texinfo on a region.)  @comment %**start of header (This is for running Texinfo on a region.)
 @setfilename gforth-info  @setfilename gforth.info
 @settitle GNU Forth Manual  @settitle GNU Forth Manual
 @setchapternewpage odd  @comment @setchapternewpage odd
 @comment %**end of header (This is for running Texinfo on a region.)  @comment %**end of header (This is for running Texinfo on a region.)
   
 @ifinfo  @ifinfo
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 option @code{--no-rc} is given; this file is first searched in @file{.},  option @code{--no-rc} is given; this file is first searched in @file{.},
 then in @file{~}, then in the normal path (see above).  then in @file{~}, then in the normal path (see above).
   
 @node Words,  , Invocation, Top  @node Words, ANS conformance, Invocation, Top
 @chapter Forth Words  @chapter Forth Words
   
 @menu  @menu
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 * Stack Manipulation::  * Stack Manipulation::
 * Memory access::  * Memory access::
 * Control Structures::  * Control Structures::
 * Local Variables::  * Locals::
 * Defining Words::  * Defining Words::
 * Vocabularies::  * Wordlists::
 * Files::  * Files::
 * Blocks::  * Blocks::
 * Other I/O::  * Other I/O::
 * Programming Tools::  * Programming Tools::
   * Threading Words::
 @end menu  @end menu
   
 @node Notation, Arithmetic, Words, Words  @node Notation, Arithmetic, Words, Words
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 The Forth words are described in this section in the glossary notation  The Forth words are described in this section in the glossary notation
 that has become a de-facto standard for Forth texts, i.e.  that has become a de-facto standard for Forth texts, i.e.
   
 @quotation  @format
 @var{word}     @var{Stack effect}   @var{wordset}   @var{pronunciation}  @var{word}     @var{Stack effect}   @var{wordset}   @var{pronunciation}
   @end format
 @var{Description}  @var{Description}
 @end quotation  
   
 @table @var  @table @var
 @item word  @item word
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 A description of the behaviour of the word.  A description of the behaviour of the word.
 @end table  @end table
   
 The name of a stack item corresponds in the following way with its type:  The type of a stack item is specified by the character(s) the name
   starts with:
   
 @table @code  @table @code
 @item name starts with  
 Type  
 @item f  @item f
 Bool, i.e. @code{false} or @code{true}.  Bool, i.e. @code{false} or @code{true}.
 @item c  @item c
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 Pointer to a name structure  Pointer to a name structure
 @end table  @end table
   
 @node Arithmetic,  , Notation, Words  @node Arithmetic, Stack Manipulation, Notation, Words
 @section Arithmetic  @section Arithmetic
 Forth arithmetic is not checked, i.e., you will not hear about integer  Forth arithmetic is not checked, i.e., you will not hear about integer
 overflow on addition or multiplication, you may hear about division by  overflow on addition or multiplication, you may hear about division by
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 operators. If you perform division with potentially negative operands,  operators. If you perform division with potentially negative operands,
 you do not want to use @code{/} or @code{/mod} with its undefined  you do not want to use @code{/} or @code{/mod} with its undefined
 behaviour, but rather @code{fm/mod} or @code{sm/mod} (probably the  behaviour, but rather @code{fm/mod} or @code{sm/mod} (probably the
 former).  former, @pxref{Mixed precision}).
   
   @menu
   * Single precision::
   * Bitwise operations::
   * Mixed precision::             operations with single and double-cell integers
   * Double precision::            Double-cell integer arithmetic
   * Floating Point::
   @end menu
   
   @node Single precision, Bitwise operations, Arithmetic, Arithmetic
 @subsection Single precision  @subsection Single precision
 doc-+  doc-+
 doc--  doc--
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 doc-min  doc-min
 doc-max  doc-max
   
   @node Bitwise operations, Mixed precision, Single precision, Arithmetic
 @subsection Bitwise operations  @subsection Bitwise operations
 doc-and  doc-and
 doc-or  doc-or
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 doc-2*  doc-2*
 doc-2/  doc-2/
   
   @node Mixed precision, Double precision, Bitwise operations, Arithmetic
 @subsection Mixed precision  @subsection Mixed precision
 doc-m+  doc-m+
 doc-*/  doc-*/
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 doc-fm/mod  doc-fm/mod
 doc-sm/rem  doc-sm/rem
   
   @node Double precision, Floating Point, Mixed precision, Arithmetic
 @subsection Double precision  @subsection Double precision
 doc-d+  doc-d+
 doc-d-  doc-d-
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 doc-dmin  doc-dmin
 doc-dmax  doc-dmax
   
 @node Stack Manipulation,,,  @node Floating Point,  , Double precision, Arithmetic
   @subsection Floating Point
   
   Angles in floating point operations are given in radians (a full circle
   has 2 pi radians). Note, that gforth has a separate floating point
   stack, but we use the unified notation.
   
   Floating point numbers have a number of unpleasant surprises for the
   unwary (e.g., floating point addition is not associative) and even a few
   for the wary. You should not use them unless you know what you are doing
   or you don't care that the results you get are totally bogus. If you
   want to learn about the problems of floating point numbers (and how to
   avoid them), you might start with @cite{David (?) Goldberg, What Every
   Computer Scientist Should Know About Floating-Point Arithmetic, ACM
   Computing Surveys 23(1):5@minus{}48, March 1991}.
   
   doc-f+
   doc-f-
   doc-f*
   doc-f/
   doc-fnegate
   doc-fabs
   doc-fmax
   doc-fmin
   doc-floor
   doc-fround
   doc-f**
   doc-fsqrt
   doc-fexp
   doc-fexpm1
   doc-fln
   doc-flnp1
   doc-flog
   doc-falog
   doc-fsin
   doc-fcos
   doc-fsincos
   doc-ftan
   doc-fasin
   doc-facos
   doc-fatan
   doc-fatan2
   doc-fsinh
   doc-fcosh
   doc-ftanh
   doc-fasinh
   doc-facosh
   doc-fatanh
   
   @node Stack Manipulation, Memory access, Arithmetic, Words
 @section Stack Manipulation  @section Stack Manipulation
   
 gforth has a data stack (aka parameter stack) for characters, cells,  gforth has a data stack (aka parameter stack) for characters, cells,
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 additional difficulty, you don't know how many cells a floating point  additional difficulty, you don't know how many cells a floating point
 number takes. It is reportedly possible to write words in a way that  number takes. It is reportedly possible to write words in a way that
 they work also for a unified stack model, but we do not recommend trying  they work also for a unified stack model, but we do not recommend trying
 it. Also, a Forth system is allowed to keep the local variables on the  it. Instead, just say that your program has an environmental dependency
   on a separate FP stack.
   
   Also, a Forth system is allowed to keep the local variables on the
 return stack. This is reasonable, as local variables usually eliminate  return stack. This is reasonable, as local variables usually eliminate
 the need to use the return stack explicitly. So, if you want to produce  the need to use the return stack explicitly. So, if you want to produce
 a standard complying program and if you are using local variables in a  a standard complying program and if you are using local variables in a
 word, forget about return stack manipulations in that word (see the  word, forget about return stack manipulations in that word (see the
 standard document for the exact rules).  standard document for the exact rules).
   
   @menu
   * Data stack::
   * Floating point stack::
   * Return stack::
   * Locals stack::
   * Stack pointer manipulation::
   @end menu
   
   @node Data stack, Floating point stack, Stack Manipulation, Stack Manipulation
 @subsection Data stack  @subsection Data stack
 doc-drop  doc-drop
 doc-nip  doc-nip
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 doc-2swap  doc-2swap
 doc-2rot  doc-2rot
   
   @node Floating point stack, Return stack, Data stack, Stack Manipulation
 @subsection Floating point stack  @subsection Floating point stack
 doc-fdrop  doc-fdrop
 doc-fnip  doc-fnip
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 doc-fswap  doc-fswap
 doc-frot  doc-frot
   
   @node Return stack, Locals stack, Floating point stack, Stack Manipulation
 @subsection Return stack  @subsection Return stack
 doc->r  doc->r
 doc-r>  doc-r>
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 doc-2r@  doc-2r@
 doc-2rdrop  doc-2rdrop
   
   @node Locals stack, Stack pointer manipulation, Return stack, Stack Manipulation
 @subsection Locals stack  @subsection Locals stack
   
   @node Stack pointer manipulation,  , Locals stack, Stack Manipulation
 @subsection Stack pointer manipulation  @subsection Stack pointer manipulation
 doc-sp@  doc-sp@
 doc-sp!  doc-sp!
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 doc-lp@  doc-lp@
 doc-lp!  doc-lp!
   
 @node Memory access  @node Memory access, Control Structures, Stack Manipulation, Words
 @section Memory access  @section Memory access
   
   @menu
   * Stack-Memory transfers::
   * Address arithmetic::
   * Memory block access::
   @end menu
   
   @node Stack-Memory transfers, Address arithmetic, Memory access, Memory access
 @subsection Stack-Memory transfers  @subsection Stack-Memory transfers
   
 doc-@  doc-@
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 doc-df@  doc-df@
 doc-df!  doc-df!
   
   @node Address arithmetic, Memory block access, Stack-Memory transfers, Memory access
 @subsection Address arithmetic  @subsection Address arithmetic
   
 ANS Forth does not specify the sizes of the data types. Instead, it  ANS Forth does not specify the sizes of the data types. Instead, it
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 doc-dfaligned  doc-dfaligned
 doc-address-unit-bits  doc-address-unit-bits
   
   @node Memory block access,  , Address arithmetic, Memory access
 @subsection Memory block access  @subsection Memory block access
   
 doc-move  doc-move
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 doc-fill  doc-fill
 doc-blank  doc-blank
   
 @node Control Structures  @node Control Structures, Locals, Memory access, Words
 @section Control Structures  @section Control Structures
   
 Control structures in Forth cannot be used in interpret state, only in  Control structures in Forth cannot be used in interpret state, only in
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 limitation, but have not seen a satisfying way around it yet, although  limitation, but have not seen a satisfying way around it yet, although
 many schemes have been proposed.  many schemes have been proposed.
   
   @menu
   * Selection::
   * Simple Loops::
   * Counted Loops::
   * Arbitrary control structures::
   * Calls and returns::
   * Exception Handling::
   @end menu
   
   @node Selection, Simple Loops, Control Structures, Control Structures
 @subsection Selection  @subsection Selection
   
 @example  @example
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 ENDIF  ENDIF
 @end example  @end example
   
 You can use @code{THEN} instead of {ENDIF}. Indeed, @code{THEN} is  You can use @code{THEN} instead of @code{ENDIF}. Indeed, @code{THEN} is
 standard, and @code{ENDIF} is not, although it is quite popular. We  standard, and @code{ENDIF} is not, although it is quite popular. We
 recommend using @code{ENDIF}, because it is less confusing for people  recommend using @code{ENDIF}, because it is less confusing for people
 who also know other languages (and is not prone to reinforcing negative  who also know other languages (and is not prone to reinforcing negative
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 CASE  CASE
   @var{n1} OF @var{code1} ENDOF    @var{n1} OF @var{code1} ENDOF
   @var{n2} OF @var{code2} ENDOF    @var{n2} OF @var{code2} ENDOF
   @dots    @dots{}
 ENDCASE  ENDCASE
 @end example  @end example
   
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 the last @code{ENDOF}. It may use @var{n}, which is on top of the stack,  the last @code{ENDOF}. It may use @var{n}, which is on top of the stack,
 but must not consume it.  but must not consume it.
   
   @node Simple Loops, Counted Loops, Selection, Control Structures
 @subsection Simple Loops  @subsection Simple Loops
   
 @example  @example
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 This is an endless loop.  This is an endless loop.
   
   @node Counted Loops, Arbitrary control structures, Simple Loops, Control Structures
 @subsection Counted Loops  @subsection Counted Loops
   
 The basic counted loop is:  The basic counted loop is:
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 @var{n}. One alternative is @code{@var{n} S+LOOP}, where the negative  @var{n}. One alternative is @code{@var{n} S+LOOP}, where the negative
 case behaves symmetrical to the positive case:  case behaves symmetrical to the positive case:
   
 @code{-2 0 ?DO  i .  -1 +LOOP}  prints @code{0 -1}  @code{-2 0 ?DO  i .  -1 S+LOOP}  prints @code{0 -1}
   
 @code{-1 0 ?DO  i .  -1 +LOOP}  prints @code{0}  @code{-1 0 ?DO  i .  -1 S+LOOP}  prints @code{0}
   
 @code{ 0 0 ?DO  i .  -1 +LOOP}  prints nothing  @code{ 0 0 ?DO  i .  -1 S+LOOP}  prints nothing
   
 The loop is terminated when the border between @var{limit@minus{}sgn(n)} and  The loop is terminated when the border between @var{limit@minus{}sgn(n)} and
 @var{limit} is crossed. However, @code{S+LOOP} is not part of the ANS  @var{limit} is crossed. However, @code{S+LOOP} is not part of the ANS
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 and ending with 0. Other Forth systems may behave differently, even if  and ending with 0. Other Forth systems may behave differently, even if
 they support @code{FOR} loops.  they support @code{FOR} loops.
   
   @node Arbitrary control structures, Calls and returns, Counted Loops, Control Structures
 @subsection Arbitrary control structures  @subsection Arbitrary control structures
   
 ANS Forth permits and supports using control structures in a non-nested  ANS Forth permits and supports using control structures in a non-nested
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 every @code{?DO} etc. there is exactly one @code{UNLOOP} on any path  every @code{?DO} etc. there is exactly one @code{UNLOOP} on any path
 through the definition (@code{LOOP} etc. compile an @code{UNLOOP} on the  through the definition (@code{LOOP} etc. compile an @code{UNLOOP} on the
 fall-through path). Also, you have to ensure that all @code{LEAVE}s are  fall-through path). Also, you have to ensure that all @code{LEAVE}s are
 resolved (by using one of the loop-ending words or @code{UNDO}).  resolved (by using one of the loop-ending words or @code{DONE}).
   
 Another group of control structure words are  Another group of control structure words are
   
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 @code{WHILE} are predefined, so in this example it would not be  @code{WHILE} are predefined, so in this example it would not be
 necessary to define them.  necessary to define them.
   
   @node Calls and returns, Exception Handling, Arbitrary control structures, Control Structures
 @subsection Calls and returns  @subsection Calls and returns
   
 A definition can be called simply be writing the name of the  A definition can be called simply be writing the name of the
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 doc-;s  doc-;s
   
   @node Exception Handling,  , Calls and returns, Control Structures
 @subsection Exception Handling  @subsection Exception Handling
   
 doc-catch  doc-catch
 doc-throw  doc-throw
   
 @node Locals  @node Locals, Defining Words, Control Structures, Words
 @section Locals  @section Locals
   
 Local variables can make Forth programming more enjoyable and Forth  Local variables can make Forth programming more enjoyable and Forth
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 implemented the ANS Forth locals wordset through our locals wordset).  implemented the ANS Forth locals wordset through our locals wordset).
   
 @menu  @menu
   * gforth locals::
   * ANS Forth locals::
 @end menu  @end menu
   
   @node gforth locals, ANS Forth locals, Locals, Locals
 @subsection gforth locals  @subsection gforth locals
   
 Locals can be defined with  Locals can be defined with
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 Currently there is no way to define locals with user-defined data  Currently there is no way to define locals with user-defined data
 structures, but we are working on it.  structures, but we are working on it.
   
 GNU Forth allows defining locals everywhere in a colon definition. This poses the following questions:  GNU Forth allows defining locals everywhere in a colon definition. This
   poses the following questions:
   
   @menu
   * Where are locals visible by name?::
   * How long do locals live? ::
   * Programming Style::
   * Implementation::
   @end menu
   
   @node Where are locals visible by name?, How long do locals live?, gforth locals, gforth locals
 @subsubsection Where are locals visible by name?  @subsubsection Where are locals visible by name?
   
 Basically, the answer is that locals are visible where you would expect  Basically, the answer is that locals are visible where you would expect
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 BEGIN  BEGIN
   x    x
 [ 1 CS-ROLL ] THEN  [ 1 CS-ROLL ] THEN
   { x }    @{ x @}
   ...    ...
 UNTIL  UNTIL
 @end example  @end example
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 warns the user if it was too optimisitic:  warns the user if it was too optimisitic:
 @example  @example
 IF  IF
   { x }    @{ x @}
 BEGIN  BEGIN
   \ x ?    \ x ?
 [ 1 cs-roll ] THEN  [ 1 cs-roll ] THEN
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 @example  @example
 IF  IF
   SCOPE    SCOPE
   { x }    @{ x @}
   ENDSCOPE    ENDSCOPE
 BEGIN  BEGIN
 [ 1 cs-roll ] THEN  [ 1 cs-roll ] THEN
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 E.g.,  E.g.,
 @example  @example
 { x }  @{ x @}
 AHEAD  AHEAD
 ASSUME-LIVE  ASSUME-LIVE
 BEGIN  BEGIN
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 arranged into:  arranged into:
 @example  @example
 BEGIN  BEGIN
   { x }    @{ x @}
   ... 0=    ... 0=
 WHILE  WHILE
   x    x
 REPEAT  REPEAT
 @end example  @end example
   
   @node How long do locals live?, Programming Style, Where are locals visible by name?, gforth locals
 @subsubsection How long do locals live?  @subsubsection How long do locals live?
   
 The right answer for the lifetime question would be: A local lives at  The right answer for the lifetime question would be: A local lives at
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 afterwards its address is invalid (and programs that access it  afterwards its address is invalid (and programs that access it
 afterwards are erroneous).  afterwards are erroneous).
   
   @node Programming Style, Implementation, How long do locals live?, gforth locals
 @subsubsection Programming Style  @subsubsection Programming Style
   
 The freedom to define locals anywhere has the potential to change  The freedom to define locals anywhere has the potential to change
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 write the items in the order you want.  write the items in the order you want.
   
 This seems a little far-fetched and eliminating stack manipulations is  This seems a little far-fetched and eliminating stack manipulations is
 unlikely to become a conscious programming objective. Still, the  unlikely to become a conscious programming objective. Still, the number
 number of stack manipulations will be reduced dramatically if local  of stack manipulations will be reduced dramatically if local variables
 variables are used liberally (e.g., compare @code{max} in \sect{misc}  are used liberally (e.g., compare @code{max} in @ref{gforth locals} with
 with a traditional implementation of @code{max}).  a traditional implementation of @code{max}).
   
 This shows one potential benefit of locals: making Forth programs more  This shows one potential benefit of locals: making Forth programs more
 readable. Of course, this benefit will only be realized if the  readable. Of course, this benefit will only be realized if the
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 Here it is clear from the start that @code{s1} has a different value  Here it is clear from the start that @code{s1} has a different value
 in every loop iteration.  in every loop iteration.
   
   @node Implementation,  , Programming Style, gforth locals
 @subsubsection Implementation  @subsubsection Implementation
   
 GNU Forth uses an extra locals stack. The most compelling reason for  GNU Forth uses an extra locals stack. The most compelling reason for
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 A special feature of GNU Forths dictionary is used to implement the  A special feature of GNU Forths dictionary is used to implement the
 definition of locals without type specifiers: every wordlist (aka  definition of locals without type specifiers: every wordlist (aka
 vocabulary) has its own methods for searching  vocabulary) has its own methods for searching
 etc. (@xref{dictionary}). For the present purpose we defined a wordlist  etc. (@pxref{Wordlists}). For the present purpose we defined a wordlist
 with a special search method: When it is searched for a word, it  with a special search method: When it is searched for a word, it
 actually creates that word using @code{W:}. @code{@{} changes the search  actually creates that word using @code{W:}. @code{@{} changes the search
 order to first search the wordlist containing @code{@}}, @code{W:} etc.,  order to first search the wordlist containing @code{@}}, @code{W:} etc.,
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 @code{lp+!#} orig-locals-size @minus{} new-locals-size  @code{lp+!#} orig-locals-size @minus{} new-locals-size
 @end format  @end format
 The second @code{lp+!#} adjusts the locals stack pointer from the  The second @code{lp+!#} adjusts the locals stack pointer from the
 level at the {\em orig} point to the level after the @code{THEN}. The  level at the @var{orig} point to the level after the @code{THEN}. The
 first @code{lp+!#} adjusts the locals stack pointer from the current  first @code{lp+!#} adjusts the locals stack pointer from the current
 level to the level at the orig point, so the complete effect is an  level to the level at the orig point, so the complete effect is an
 adjustment from the current level to the right level after the  adjustment from the current level to the right level after the
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 usually less than reclaiming this space would cost in code size.  usually less than reclaiming this space would cost in code size.
   
   
   @node ANS Forth locals,  , gforth locals, Locals
 @subsection ANS Forth locals  @subsection ANS Forth locals
   
 The ANS Forth locals wordset does not define a syntax for locals, but  The ANS Forth locals wordset does not define a syntax for locals, but
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 @end itemize  @end itemize
   
 Locals defined in this way behave like @code{VALUE}s  Locals defined in this way behave like @code{VALUE}s
 (@xref{values}). I.e., they are initialized from the stack. Using their  (@xref{Values}). I.e., they are initialized from the stack. Using their
 name produces their value. Their value can be changed using @code{TO}.  name produces their value. Their value can be changed using @code{TO}.
   
 Since this syntax is supported by gforth directly, you need not do  Since this syntax is supported by gforth directly, you need not do
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 merit of this syntax is that it is easy to implement using the ANS Forth  merit of this syntax is that it is easy to implement using the ANS Forth
 locals wordset.  locals wordset.
   
 @node Internals  @node Defining Words, Wordlists, Locals, Words
   @section Defining Words
   
   @node Values,  , Defining Words, Defining Words
   @subsection Values
   
   @node Wordlists, Files, Defining Words, Words
   @section Wordlists
   
   @node Files, Blocks, Wordlists, Words
   @section Files
   
   @node Blocks, Other I/O, Files, Words
   @section Blocks
   
   @node Other I/O, Programming Tools, Blocks, Words
   @section Other I/O
   
   @node Programming Tools, Threading Words, Other I/O, Words
   @section Programming Tools
   
   @menu
   * Debugging::                   Simple and quick.
   * Assertions::                  Making your programs self-checking.
   @end menu
   
   @node Debugging, Assertions, Programming Tools, Programming Tools
   @subsection Debugging
   
   The simple debugging aids provided in @file{debugging.fs}
   are meant to support a different style of debugging than the
   tracing/stepping debuggers used in languages with long turn-around
   times.
   
   A much better (faster) way in fast-compilig languages is to add
   printing code at well-selected places, let the program run, look at
   the output, see where things went wrong, add more printing code, etc.,
   until the bug is found.
   
   The word @code{~~} is easy to insert. It just prints debugging
   information (by default the source location and the stack contents). It
   is also easy to remove (@kbd{C-x ~} in the Emacs Forth mode to
   query-replace them with nothing). The deferred words
   @code{printdebugdata} and @code{printdebugline} control the output of
   @code{~~}. The default source location output format works well with
   Emacs' compilation mode, so you can step through the program at the
   source level using @kbd{C-x `} (the advantage over a stepping debugger
   is that you can step in any direction and you know where the crash has
   happened or where the strange data has occurred).
   
   Note that the default actions clobber the contents of the pictured
   numeric output string, so you should not use @code{~~}, e.g., between
   @code{<#} and @code{#>}.
   
   doc-~~
   doc-printdebugdata
   doc-printdebugline
   
   @node Assertions,  , Debugging, Programming Tools
   @subsection Assertions
   
   It is a good idea to make your programs self-checking, in particular, if
   you use an assumption (e.g., that a certain field of a data structure is
   never zero) that may become wrong during maintenance. GForth supports
   assertions for this purpose. They are used like this:
   
   @example
   assert( @var{flag} )
   @end example
   
   The code between @code{assert(} and @code{)} should compute a flag, that
   should be true if everything is alright and false otherwise. It should
   not change anything else on the stack. The overall stack effect of the
   assertion is @code{( -- )}. E.g.
   
   @example
   assert( 1 1 + 2 = ) \ what we learn in school
   assert( dup 0<> ) \ assert that the top of stack is not zero
   assert( false ) \ this code should not be reached
   @end example
   
   The need for assertions is different at different times. During
   debugging, we want more checking, in production we sometimes care more
   for speed. Therefore, assertions can be turned off, i.e., the assertion
   becomes a comment. Depending on the importance of an assertion and the
   time it takes to check it, you may want to turn off some assertions and
   keep others turned on. GForth provides several levels of assertions for
   this purpose:
   
   doc-assert0(
   doc-assert1(
   doc-assert2(
   doc-assert3(
   doc-assert(
   doc-)
   
   @code{Assert(} is the same as @code{assert1(}. The variable
   @code{assert-level} specifies the highest assertions that are turned
   on. I.e., at the default @code{assert-level} of one, @code{assert0(} and
   @code{assert1(} assertions perform checking, while @code{assert2(} and
   @code{assert3(} assertions are treated as comments.
   
   Note that the @code{assert-level} is evaluated at compile-time, not at
   run-time. I.e., you cannot turn assertions on or off at run-time, you
   have to set the @code{assert-level} appropriately before compiling a
   piece of code. You can compile several pieces of code at several
   @code{assert-level}s (e.g., a trusted library at level 1 and newly
   written code at level 3).
   
   doc-assert-level
   
   If an assertion fails, a message compatible with Emacs' compilation mode
   is produced and the execution is aborted (currently with @code{ABORT"}.
   If there is interest, we will introduce a special throw code. But if you
   intend to @code{catch} a specific condition, using @code{throw} is
   probably more appropriate than an assertion).
   
   @node Threading Words,  , Programming Tools, Words
   @section Threading Words
   
   These words provide access to code addresses and other threading stuff
   in gforth (and, possibly, other interpretive Forths). It more or less
   abstracts away the differences between direct and indirect threading
   (and, for direct threading, the machine dependences). However, at
   present this wordset is still inclomplete. It is also pretty low-level;
   some day it will hopefully be made unnecessary by an internals words set
   that abstracts implementation details away completely.
   
   doc->code-address
   doc->does-code
   doc-code-address!
   doc-does-code!
   doc-does-handler!
   doc-/does-handler
   
   @node ANS conformance, Model, Words, Top
   @chapter ANS conformance
   
   @node Model, Emacs and GForth, ANS conformance, Top
   @chapter Model
   
   @node Emacs and GForth, Internals, Model, Top
   @chapter Emacs and GForth
   
   GForth comes with @file{gforth.el}, an improved version of
   @file{forth.el} by Goran Rydqvist (icluded in the TILE package). The
   improvements are a better (but still not perfect) handling of
   indentation. I have also added comment paragraph filling (@kbd{M-q}),
   commenting (@kbd{C-x \}) and uncommenting (@kbd{C-x |}) regions and
   removing debugging tracers (@kbd{C-x ~}). I left the stuff I do not use
   alone, even though some of it only makes sense for TILE. To get a
   description of these features, enter Forth mode and type @kbd{C-h m}.
   
   In addition, GForth supports Emacs quite well: The source code locations
   given in error messages, debugging output (from @code{~~}) and failed
   assertion messages are in the right format for Emacs' compilation mode
   (@pxref{Compilation, , Running Compilations under Emacs, emacs, Emacs
   Manual}) so the source location corresponding to an error or other
   message is only a few keystrokes away (@kbd{C-x `} for the next error,
   @kbd{C-c C-c} for the error under the cursor).
   
   Also, if you @code{include} @file{etags.fs}, a new @file{TAGS} file
   (@pxref{Tags, , Tags Tables, emacs, Emacs Manual}) will be produced that
   contains the definitions of all words defined afterwards. You can then
   find the source for a word using @kbd{M-.}. Note that emacs can use
   several tags files at the same time (e.g., one for the gforth sources
   and one for your program).
   
   To get all these benefits, add the following lines to your @file{.emacs}
   file:
   
   @example
   (autoload 'forth-mode "gforth.el")
   (setq auto-mode-alist (cons '("\\.fs\\'" . forth-mode) auto-mode-alist))
   @end example
   
   @node Internals, Bugs, Emacs and GForth, Top
 @chapter Internals  @chapter Internals
   
 Reading this section is not necessary for programming with gforth. It  Reading this section is not necessary for programming with gforth. It
 should be helpful for finding your way in the gforth sources.  should be helpful for finding your way in the gforth sources.
   
   @menu
   * Portability::
   * Threading::
   * Primitives::
   * System Architecture::
   @end menu
   
   @node Portability, Threading, Internals, Internals
 @section Portability  @section Portability
   
 One of the main goals of the effort is availability across a wide range  One of the main goals of the effort is availability across a wide range
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 unimportant) UNIX machines, VMS, 80386s running MS-DOS, the Amiga, and  unimportant) UNIX machines, VMS, 80386s running MS-DOS, the Amiga, and
 the Atari ST, so a Forth written in GNU C can run on all these  the Atari ST, so a Forth written in GNU C can run on all these
 machines@footnote{Due to Apple's look-and-feel lawsuit it is not  machines@footnote{Due to Apple's look-and-feel lawsuit it is not
 available on the Mac (@pxref{Boycott, , Protect Your Freedom--Fight  available on the Mac (@pxref{Boycott, , Protect Your Freedom---Fight
 ``Look And Feel'', gcc.info, GNU C Manual}).}.  ``Look And Feel'', gcc.info, GNU C Manual}).}.
   
 Writing in a portable language has the reputation of producing code that  Writing in a portable language has the reputation of producing code that
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 explicit register declarations are used. So by default  explicit register declarations are used. So by default
 @code{-DFORCE_REG} is not used.  @code{-DFORCE_REG} is not used.
   
   @node Threading, Primitives, Portability, Internals
 @section Threading  @section Threading
   
 GNU C's labels as values extension (available since @code{gcc-2.0},  GNU C's labels as values extension (available since @code{gcc-2.0},
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 Of course we have packaged the whole thing neatly in macros called  Of course we have packaged the whole thing neatly in macros called
 @code{NEXT} and @code{NEXT1} (the part of NEXT after fetching the cfa).  @code{NEXT} and @code{NEXT1} (the part of NEXT after fetching the cfa).
   
   @menu
   * Scheduling::
   * Direct or Indirect Threaded?::
   * DOES>::
   @end menu
   
   @node Scheduling, Direct or Indirect Threaded?, Threading, Threading
 @subsection Scheduling  @subsection Scheduling
   
 There is a little complication: Pipelined and superscalar processors,  There is a little complication: Pipelined and superscalar processors,
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 the NEXT comes strictly after the other code, i.e., there is nearly no  the NEXT comes strictly after the other code, i.e., there is nearly no
 scheduling. After a little thought the problem becomes clear: The  scheduling. After a little thought the problem becomes clear: The
 compiler cannot know that sp and ip point to different addresses (and  compiler cannot know that sp and ip point to different addresses (and
 the version of @code{gcc} we used would not know it even if it could),  the version of @code{gcc} we used would not know it even if it was
 so it could not move the load of the cfa above the store to the  possible), so it could not move the load of the cfa above the store to
 TOS. Indeed the pointers could be the same, if code on or very near the  the TOS. Indeed the pointers could be the same, if code on or very near
 top of stack were executed. In the interest of speed we chose to forbid  the top of stack were executed. In the interest of speed we chose to
 this probably unused ``feature'' and helped the compiler in scheduling:  forbid this probably unused ``feature'' and helped the compiler in
 NEXT is divided into the loading part (@code{NEXT_P1}) and the goto part  scheduling: NEXT is divided into the loading part (@code{NEXT_P1}) and
 (@code{NEXT_P2}). @code{+} now looks like:  the goto part (@code{NEXT_P2}). @code{+} now looks like:
 @example  @example
 n=sp[0]+sp[1];  n=sp[0]+sp[1];
 sp++;  sp++;
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 sp[0]=n;  sp[0]=n;
 NEXT_P2;  NEXT_P2;
 @end example  @end example
 This can be scheduled optimally by the compiler (see \sect{TOS}).  This can be scheduled optimally by the compiler.
   
 This division can be turned off with the switch @code{-DCISC_NEXT}. This  This division can be turned off with the switch @code{-DCISC_NEXT}. This
 switch is on by default on machines that do not profit from scheduling  switch is on by default on machines that do not profit from scheduling
 (e.g., the 80386), in order to preserve registers.  (e.g., the 80386), in order to preserve registers.
   
   @node Direct or Indirect Threaded?, DOES>, Scheduling, Threading
 @subsection Direct or Indirect Threaded?  @subsection Direct or Indirect Threaded?
   
 Both! After packaging the nasty details in macro definitions we  Both! After packaging the nasty details in macro definitions we
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 lines. I.e., even porting direct threading to a new machine is a small  lines. I.e., even porting direct threading to a new machine is a small
 effort.  effort.
   
   @node DOES>,  , Direct or Indirect Threaded?, Threading
 @subsection DOES>  @subsection DOES>
 One of the most complex parts of a Forth engine is @code{dodoes}, i.e.,  One of the most complex parts of a Forth engine is @code{dodoes}, i.e.,
 the chunk of code executed by every word defined by a  the chunk of code executed by every word defined by a
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 a cell unused in most words is a bit wasteful, but on the machines we  a cell unused in most words is a bit wasteful, but on the machines we
 are targetting this is hardly a problem. The other reason for having a  are targetting this is hardly a problem. The other reason for having a
 code field size of two cells is to avoid having different image files  code field size of two cells is to avoid having different image files
 for direct and indirect threaded systems (@pxref{image-format}).  for direct and indirect threaded systems (@pxref{System Architecture}).
   
 The other approach is that the code field points or jumps to the cell  The other approach is that the code field points or jumps to the cell
 after @code{DOES}. In this variant there is a jump to @code{dodoes} at  after @code{DOES}. In this variant there is a jump to @code{dodoes} at
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 this approach for direct threading. We did not want to add another  this approach for direct threading. We did not want to add another
 cell to the code field.  cell to the code field.
   
   @node Primitives, System Architecture, Threading, Internals
 @section Primitives  @section Primitives
   
   @menu
   * Automatic Generation::
   * TOS Optimization::
   * Produced code::
   @end menu
   
   @node Automatic Generation, TOS Optimization, Primitives, Primitives
 @subsection Automatic Generation  @subsection Automatic Generation
   
 Since the primitives are implemented in a portable language, there is no  Since the primitives are implemented in a portable language, there is no
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 @example  @example
 I_plus: /* + ( n1 n2 -- n ) */  /* label, stack effect */  I_plus: /* + ( n1 n2 -- n ) */  /* label, stack effect */
 /*  */                          /* documentation */  /*  */                          /* documentation */
 {  @{
 DEF_CA                          /* definition of variable ca (indirect threading) */  DEF_CA                          /* definition of variable ca (indirect threading) */
 Cell n1;                        /* definitions of variables */  Cell n1;                        /* definitions of variables */
 Cell n2;  Cell n2;
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 n2 = (Cell) TOS;  n2 = (Cell) TOS;
 sp += 1;                        /* stack adjustment */  sp += 1;                        /* stack adjustment */
 NAME("+")                       /* debugging output (with -DDEBUG) */  NAME("+")                       /* debugging output (with -DDEBUG) */
 {  @{
 n = n1+n2;                      /* C code taken from the source */  n = n1+n2;                      /* C code taken from the source */
 }  @}
 NEXT_P1;                        /* NEXT part 1 */  NEXT_P1;                        /* NEXT part 1 */
 TOS = (Cell)n;                  /* output */  TOS = (Cell)n;                  /* output */
 NEXT_P2;                        /* NEXT part 2 */  NEXT_P2;                        /* NEXT part 2 */
 }  @}
 @end example  @end example
   
 This looks long and inefficient, but the GNU C compiler optimizes quite  This looks long and inefficient, but the GNU C compiler optimizes quite
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 account, most notably @code{?dup}, but also words that do not (always)  account, most notably @code{?dup}, but also words that do not (always)
 fall through to NEXT.  fall through to NEXT.
   
   @node TOS Optimization, Produced code, Automatic Generation, Primitives
 @subsection TOS Optimization  @subsection TOS Optimization
   
 An important optimization for stack machine emulators, e.g., Forth  An important optimization for stack machine emulators, e.g., Forth
 engines, is keeping  one or more of the top stack items in  engines, is keeping  one or more of the top stack items in
 registers.  If a word has the stack effect {@var{in1}...@var{inx} @code{--}  registers.  If a word has the stack effect @var{in1}...@var{inx} @code{--}
 @var{out1}...@var{outy}}, keeping the top @var{n} items in registers  @var{out1}...@var{outy}, keeping the top @var{n} items in registers
 @itemize  @itemize
 @item  @item
 is better than keeping @var{n-1} items, if @var{x>=n} and @var{y>=n},  is better than keeping @var{n-1} items, if @var{x>=n} and @var{y>=n},
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 @item In the case of @code{dup ( w -- w w )} the generator must not  @item In the case of @code{dup ( w -- w w )} the generator must not
 eliminate the store to the original location of the item on the stack,  eliminate the store to the original location of the item on the stack,
 if the TOS optimization is turned on.  if the TOS optimization is turned on.
 @item Primitives with stack effects of the form {@code{--}  @item Primitives with stack effects of the form @code{--}
 @var{out1}...@var{outy}} must store the TOS to the stack at the start.  @var{out1}...@var{outy} must store the TOS to the stack at the start.
 Likewise, primitives with the stack effect {@var{in1}...@var{inx} @code{--}}  Likewise, primitives with the stack effect @var{in1}...@var{inx} @code{--}
 must load the TOS from the stack at the end. But for the null stack  must load the TOS from the stack at the end. But for the null stack
 effect @code{--} no stores or loads should be generated.  effect @code{--} no stores or loads should be generated.
 @end itemize  @end itemize
   
   @node Produced code,  , TOS Optimization, Primitives
 @subsection Produced code  @subsection Produced code
   
 To see what assembly code is produced for the primitives on your machine  To see what assembly code is produced for the primitives on your machine
 with your compiler and your flag settings, type @code{make engine.s} and  with your compiler and your flag settings, type @code{make engine.s} and
 look at the resulting file @file{engine.c}.  look at the resulting file @file{engine.s}.
   
   @node System Architecture,  , Primitives, Internals
 @section System Architecture  @section System Architecture
   
 Our Forth system consists not only of primitives, but also of  Our Forth system consists not only of primitives, but also of
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 image file that enables the loader to change the byte order.}.  image file that enables the loader to change the byte order.}.
   
 Forth code that is going to end up in a portable image file has to  Forth code that is going to end up in a portable image file has to
 comply to some restrictions: addresses have to be stored in memory  comply to some restrictions: addresses have to be stored in memory with
 with special words (@code{A!}, @code{A,}, etc.) in order to make the  special words (@code{A!}, @code{A,}, etc.) in order to make the code
 code relocatable. Cells, floats, etc., have to be stored at the  relocatable. Cells, floats, etc., have to be stored at the natural
 natural alignment boundaries@footnote{E.g., store floats (8 bytes) at  alignment boundaries@footnote{E.g., store floats (8 bytes) at an address
 an address dividable by~8. This happens automatically in our system  dividable by~8. This happens automatically in our system when you use
 when you use the ANSI alignment words.}, in order to avoid alignment  the ANS Forth alignment words.}, in order to avoid alignment faults on
 faults on machines with stricter alignment. The image file is produced  machines with stricter alignment. The image file is produced by a
 by a metacompiler (@file{cross.fs}).  metacompiler (@file{cross.fs}).
   
 So, unlike the image file of Mitch Bradleys @code{cforth}, our image  So, unlike the image file of Mitch Bradleys @code{cforth}, our image
 file is not directly executable, but has to undergo some manipulations  file is not directly executable, but has to undergo some manipulations
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 primitive calls with the appropriate code-field addresses (or code  primitive calls with the appropriate code-field addresses (or code
 addresses in the case of direct threading).  addresses in the case of direct threading).
   
   @node Bugs, Pedigree, Internals, Top
   @chapter Bugs
   
   @node Pedigree, Word Index, Bugs, Top
   @chapter Pedigree
   
   @node Word Index, Node Index, Pedigree, Top
   @chapter Word Index
   
   @node Node Index,  , Word Index, Top
   @chapter Node Index
   
 @contents  @contents
 @bye  @bye
   

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