header wordset

description

Implements header creation and navigation and defer/synonym words.

Copyright (C) Tektronix, Inc. 1998 - 2001. All rights reserved.

FORTH

BODY> ( pfa -- cfa )();
p4:"body-from";

trying to convert a pointer to the parameter-field (PFA) to point then to the corresponding code-field (CFA) - note that this is not necessarily the inverse of >BODY instead it is a fast implementation assuming a VARIABLE thing had been used. Every use of "BODY>" is warned in the logfile.

 implementation-specific simulation:
   : BODY> CELL - ;
FORTH

>LINK ( cfa -- lfa )();
p4:"to-link";

converts a pointer to the code-field (CFA) to point then to the corresponding link-field (LFA) - in some configurations this can be a very slow operation since the system might need to walk through all header-words in the system, looking for a >NAME that has the cfa and *then* returning the "N>LINK" result here - which might be none at all if the word is a :NONAME. Use always >NAME and treat this word as non-portable just like any assumption about the contents of the >LINK-field. Only in fig-mode and for traditional fig-mode programs, this word may possibly have enough extra assertions to be somewhat reliable. (and fig-mode did not know about SYNONYMs - see note at LINK>).

FORTH

LINK> ( lfa -- cfa )();
p4:"link-from";

converts a pointer to the link-field (LFA) to point then to the corresponding code-field (CFA)

BEWARE: this one does not care about SYNONYMs and it is the only way to get at the data of a SYNONYM. Therefore, if you have a synonym called A for an old word B then there is a different result using "NAME>" on an A-nfa or using "N>LINK LINK>" since the first "NAME>" will return the xt of B while the latter will return the xt of A - but executing an xt of A is an error and it will THROW

this difference is intentional to allow knowledgable persons to do weird things looking around in the dictionary. The forth standard words will not give you much of a chance to get hold of the nfa of a SYNONYM word anyway - asking FIND for a word A will return the execution token of B immediatly and "NAME>" on that one lead to the nfa of B and not that of A.

FORTH

>NAME ( cfa -- nfa )();
p4:"to-name";

converts a pointer to the code-field (CFA) to point then to the corresponding name-field (NFA)

 implementation-specific simulation:
   : >NAME  >LINK L>NAME ;
 
FORTH

NAME> ( nfa -- cfa )();
p4:"name-from";

converts a pointer to the name-field (NFA) to point then to the corresponding code-field (CFA) (in all cases but a SYNONYM the pfe will behave not unlike the original fig-forth did - being identical to N>LINK LINK> )

FORTH

L>NAME ( lfa -- nfa )();
p4:"l-to-name";

converts a pointer to the link-field (LFA) to point then to the corresponding name-field (CFA) - this one is one of the slowest operation available. One should always use the inverse operation N>LINK and cache an older value if that is needed. Some words might be linked but they do not have a name-field (just the other fields) but this word can not detect that and will try to look into the bits of the dictionary anway in the assumption that there is something - and if done in the wrong place it might even segfault. Only in fig-mode and for traditional fig-mode programs, this word may possibly have enough extra assertions to be somewhat reliable. (and fig-mode did not know about SYNONYMs - see note at LINK>).

 implementation-specific configure-dependent fig-only simulation:
 : L>NAME BEGIN DUP C@ 128 AND 0= WHILE 1- REPEAT ;
 
FORTH

N>LINK ( nfa -- lfa )();
p4:"n-to-link";

converts a pointer to the name-field (NFA) to point then to the corresponding link-field (LFA) - this operation is quicker than the inverse L>NAME. This word is a specific implementation detail and should not be used by normal users - instead use always NAME> which is much more portable. Many systems may possibly not even have a >LINK-field in the sense that a @ on this adress will lead to another >NAME. Any operation on the resulting >LINK-adress is even dependent on the current configuration of PFE - only in fig-mode you are asserted to have the classic detail. (and fig-mode did not know about SYNONYMs - see note at LINK>).

 implementation-specific configure-dependent fig-only simulation:
   : N>LINK  C@ + ;
 
FORTH
NAME>STRING ( name-token -- str-ptr str-len )(); 
 ;

convert a name-token into a string-span, used to detect the name for a word and print it. The word ID. can be defined as

 : ID. NAME>STRING TYPE ;

the implementation of NAME>STRING depends on the header layout that is defined during the configuration of the forth system.

 : NAME>STRING COUNT 31 AND ; ( for fig-like names )
 : NAME>STRING COUNT ;        ( default, name is a simple counted string )
 : NAME>STRING @ ZCOUNT ;     ( name-token is a pointer to a C-level string )
 : NAME>STRING COUNT 31 AND   ( hybrid of fig-like and zero-terminated )
      DUP 31 = IF DROP 1+ ZCOUNT THEN
 ;
 : NAME>STRING HEAD:: COUNT CODE:: PAD PLACE PAD ; ( different i86 segments )
FORTH

LAST ( .. )();
as:"last";

threadstate variable LAST

last (no special usage info)

FORTH

LATEST ( -- nfa )();
p4:"latest";

return the NFA of the lateset definition in the CURRENT vocabulary

EXTENSIONS

>FFA ( nfa -- ffa )obsolete();
p4:"to-ffa";

converts a pointer to the name-field (NFA) to point then to the corresponding flag-field (FFA) - in traditinal Forth this is the same address. pfe _can_ do different.

 implementation-specific configure-dependent simulation:
   : FFA  1- ;
 
EXTENSIONS
FFA> ( ffa -- nfa )obsolete(); 
 ;

converts a pointer to the flag-field (FFA) to point then to the corresponding name-field (NFA) - in traditinal Forth this is the same address. pfe _can_ do different.

 implementation-specific configure-dependent simulation:
   : FFA  1+ ;
 
EXTENSIONS
NAME-FLAGS@ ( nfa -- nfa-flags )(); 
 ;

get the nfa-flags that corresponds to the nfa given. Note that in the fig-style would include the nfa-count in the lower bits. (see NAME-FLAGS!)

EXTENSIONS
NAME-FLAGS! ( nfa-flags nfa -- )(); 
 ;

set the nfa-flags of nfa given. Note that in the fig-style the nfa-flags would include the nfa-count in the lower bits - therefore this should only set bits that had been previously retrieved with NAME-FLAGS@

 : IMMEDIATE LAST @ NAME-FLAGS@ IMMEDIATE-MASK OR LAST @ NAME-FLAGS! ;
 
EXTENSIONS
HEADER, ( str-ptr str-len -- )(); 
 ;

CREATE a new header in the dictionary from the given string, without CFA

 usage: : VARIABLE  BL WORD COUNT HEADER, DOVAR , ;
 
EXTENSIONS

$HEADER ( bstring -- )();
p4:"str-header";

CREATE a new header in the dictionary from the given string with the variable runtime (see HEADER, and CREATE:)

 usage: : VARIABLE  BL WORD $HEADER ;
 
EXTENSIONS

HEADER ( .. )();
as:"header";

obsolete forthword HEADER

is doing the same as $HEADER

This word should be replaced. It will be deleted in the near future. Instead use the (newer) synonym word given above.

EXTENSIONS

SMUDGE ( .. )();
as:"smudge";

ordinary primitive SMUDGE

an executable word (no special usage info)

or wrapper call around p4_smudge

EXTENSIONS

REVEAL ( -- )();
p4:"reveal";

the FIG definition toggles the SMUDGE bit, and not all systems have a smudge bit - instead one should use REVEAL or HIDE

 : REVEAL LAST @ FLAGS@ SMUDGE-MASK INVERT AND LAST @ FLAGS! ;
 : REVEAL LAST @ CHAIN-INTO-CURRENT ;
 
EXTENSIONS

RECURSIVE ( .. )();
as:"recursive";

immediate primitive RECURSIVE

an executable word (no special usage info)

or wrapper call around p4_reveal

EXTENSIONS

UNSMUDGE ( .. )();
as:"unsmudge";

obsolete forthword UNSMUDGE

is doing the same as REVEAL

This word should be replaced. It will be deleted in the near future. Instead use the (newer) synonym word given above.

EXTENSIONS
IMMEDIATE-MASK ( .. )(); 
 ;
( P4xIMMEDIATE )  constant IMMEDIATE-MASK

an ordinary constant (no special usage info)

EXTENSIONS
SMUDGE-MASK ( .. )(); 
 ;
( P4xSMUDGED )  constant SMUDGE-MASK

an ordinary constant (no special usage info)

EXTENSIONS
(IMMEDIATE#) ( .. )(); 
 ;

obsolete forthword (IMMEDIATE#)

is doing the same as IMMEDIATE-MASK

This word should be replaced. It will be deleted in the near future. Instead use the (newer) synonym word given above.

EXTENSIONS

(SMUDGE#) ( .. )();
as:"paren-smudge-sharp";

obsolete forthword (SMUDGE#)

is doing the same as SMUDGE-MASK

This word should be replaced. It will be deleted in the near future. Instead use the (newer) synonym word given above.

EXTENSIONS

DEFER ( 'word' -- )();
p4:"defer";

create a new word with ((DEFER))-semantics

 simulate:
   : DEFER  CREATE 0, DOES> ( the ((DEFER)) runtime ) 
      @ ?DUP IF EXECUTE THEN ;
   : DEFER  DEFER-RT HEADER 0 , ;

declare as <c>"DEFER deferword"</c> <br> and set as <c>"['] executionword IS deferword"</c> (in pfe, you can also use TO deferword to set the execution)

EXTENSIONS

IS ( xt-value [word] -- )();
p4:"is";

set a DEFER word (in pfe: set the DOES-field - which is the BODY-field in ans-mode and therefore the same as TO / in fig-mode the DOES-field is one cell higher up than for a CREATE: VARIABLE Use IS freely on each DOES-words in both modes).

 : IS ' 
   STATE @ IF LITERAL, POSTPONE >DOES-BODY POSTPONE ! 
   ELSE >DOES-BODY ! THEN 
 ; IMMEDIATE
 
EXTENSIONS

BEHAVIOR ( xt1 -- xt2 )();
p4:"behavior";

get the execution token xt2 that would be executed by the DEFER identified by xt1.

This command is used to obtain the execution contents of a deferred word. A typical use would be to retrieve and save the execution behavior of the deferred word, set the deferred word to a new behavior, and then later restore the old behavior.

If the deferred word identified by _xt1_ is associated with some other deferred word, _xt2_ is the execution token of that other deferred word. To retrieve the execution token of the word currently associated with that other deferred word, use the phrase BEHAVIOR BEHAVIOR .

Experience: Many years of use in OpenBoot and OpenFirmware systems. (Proposed for ANS Forth 2001)

In PFE it is the inverse of an IS operation and it will never fail if applied to a word with atleast a body. That's just like IS can be applied to almost every DOES> word where BEHAVIOR will get the value back.

EXTENSIONS
SYNONYM ( "newname" "oldname" -- )(); 
 ;

make an name-alias for a word - this is very different from a DEFER since a DEFER will resolve at runtime. Changing the target of a DEFER via IS will result in changing the BEHAVIOR of all words defined earlier and containing the name of the DEFER.

A SYNONYM however does not have any data field (theoretically not even an execution token), instead it gets resolved at compile time. In theory, you can try to FIND the name of the SYNONYM but as soon as you apply NAME> the execution token of the end-point is returned. This has also the effect that using the inverse >NAME operation will result in the name-token of the other name.

   SYNONYM CREATE <BUILDS ( like it is in ANS Forth )
   : FOO CREATE DOES> @ ;
   SEE FOO
   : foo <builds
     does> @ ;
   SYNONYM CREATE CREATE:
   : BAR CREATE 10 ALLOT ;
   SEE BAR
   : bar create: 10 allot ;

(only LINK> does not care about SYNONYMs)

EXTENSIONS
SYNONYM-OBSOLETED ( .. )(); 
 ;

definining primitive SYNONYM-OBSOLETED

an executable word (no special usage info)

or wrapper call around p4_obsoleted

ENVIRONMENT

HEADER-EXT ( .. )();
as:"header-minus-ext";

( 1983 )  constant HEADER-EXT

an ordinary constant (no special usage info)