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From: Julian Fondren <ayrnieu@gmail.com>
Newsgroups: comp.lang.forth
Subject: Re: factoring exercise
Date: Tue, 02 Aug 2011 17:25:13 -0500
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mlg3 <m_l_g3@yahoo.com> writes:
> Now I have to apologize: I had a false impression that all people read
> Gforth source with no problems, and I am the only one intolerant to
> dual-xts and Gforth internals. x>cflag and x>iflag are a modified
> copy-paste from the Gforth stuff like:
>
> : name>int ( nt -- xt )
>     \G @i{xt} represents the interpretation semantics of the word [...]
>     (name>x) (x>int) ;
>
>
> The most confusing thing is interpret/compile-int -- this word is not
> a variable, it is a field ( addr -- addr+off).
>
>>> : x>iflag ( cfa x1 -- xt x2 )
> cfa is called cfa but it may be used as an xt
> x1 is a set of flags
>>>[..]
> ( cfa xt )
>>>   over interpret/compile?  if drop interpret/compile-int @ -2 else
>
> here interpret/compile? takes cfa and checks if it is a dual-xt word;
> DROP -- we just discard x1, x1 is not used for dual-xt words
>
> And the line:
>
> ( cfa ) interpret-compile-int ( cfa+offset ) @ ( xt-int )
>
> explains why cfa is not called xt: the code field is a struct, and we
> fetch a value from that struct. That value also points to some
> structure, but that structure is irrelevant and we call it xt -- an
> opaque execution token.

Is it safe to fetch from the wrong field?  If so,

  : (x>flag) ( cfa x1 -- xt-c xt-i x2 )
    dup restrict-mask and    if drop dup -3 else
    over interpret/compile?  if drop dup interpret/compile-comp @
                                swap interpret/compile-int @ -2 else
    immediate-mask and       if dup -1 else
                                dup 0 then then then ;

  : x>cflag ( cfa x1 -- xt x2 )  (x>flag) nip ;
  : x>iflag ( cfa x1 -- xt x2 )  (x>flag) rot drop ;

Maybe the fields are adjacent in gforth, and you can e.g.

  if drop interpret/compile-int 2@ ( xt-c xt-i ) -2 else

Maybe you can give (X>FLAG) a nicer name and use it in place of X>CFLAG
and X>IFLAG