[retroforth] Re: 7.5 Development
- From: Stefan Schmiedl <s@xxxxxx>
- To: retroforth@xxxxxxxxxxxxx
- Date: Thu, 21 Oct 2004 18:20:37 +0200
Charles Childers (2004-10-21 10:01):
>
> >>* Should the interpreter stop executing when it encounters an unknown
> >>word, or report the error and continue?
> >>
> >>
> >
> >How about a variable controlling this behaviour?
> >
> >
> That is doable, but it would complicate the interpret routine quite a bit.
?
interpret:
.o: call query ; ( Get a WORD )
.word: upsh 32 ; ( Push a <SPACE> onto the stack )
call parse ; ( Parse until we find <SPACE> )
jnz .find ; ( Look for the end of the line )
drop ; ( DROP two numbers )
drop ;
jmp .o ; ( Loop back to start if no words found
)
.find: call find ; ( See if we can find the word )
jnc .exec ; ( Yes? Interpret it )
call number ; ( No? Then make it a number )
jnc .word ; ( Loop back )
Here we know that it's neither known nor a number.
So let's do a
call barf
where barf does something like
: unknown barf? @ 0; ." Help!" ;
drop ; ( Drop two numbers )
drop ;
jmp .o ; ( And Loop back )
.exec: upop edi ; ( This is where we actually call the )
call edi ; ( words we find )
jmp .word ; ( And Loop back )
next
>
> >do we have defer? would be another way to solve to the first
> >problem.
> >
> >
> Here are definitions for defer:
>
> : is here >r h0 ! 32 parse find compile r> h0 ! ;
> : defer create here 5 - h0 ! $90909090 , $90 1, $c3 1, ;
>
> They aren't in the core though (I don't see a need for revectored words
> in the core, especially since they're quite easy to add).
They might be easy to add, but not for me ... I don't get how
they work ... lack of assembly knowledge, probably.
> How would they
> help solve the problem with interpret?
It's even better if you have a deferred word in there,
because then the action taken can be adjusted by the user,
nothing is hardcoded. I agree that it's a violation of
early binding, but a convenient one :-)
SwiftForth has something like this, which allows you
to define a sensible "default action" for this case.
If you're counting words, you could use
: counter $create 1 , does> dup @ 1+ swap ! ;
' counter is barf
after factoring $create out of create, of course.
Default behaviour would need to be 2drop.
>
> --
> Charles
>
--
Stefan Schmiedl
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