Re: [Amforth-devel] words: tuck/under etc

[Kalus M. <mic...@on...>]

Hi Bernard.


Am 15.07.2008 um 03:03 schrieb Bernard Mentink:

> And lastly, the FSM code is:
>
> : FSM:       ( width -- )  CREATE  ,  ]
>         DOES>  ( n adr -- )
>                TUCK  @  mystate @  *   +   CELLS   CELL+  +
>                ( adr')  PERFORM  ;
>
>  I notice he enters into compile mode with the "]" word just before  
> the
> DOES> word, is that necessary to do with the latest CREATE/DOES code?

In the meantime I studied Nobles Code (1). Hope I got it right what  
he is doing there.


This is what the ] does:

He ceates a defining word called FSM: and during compiletime of FSM:  
the ] is compiled into the definition. At runtime of FSM: the ] is  
executed. Now this starts compilation of all the words following the  
word defined by the defining word until the closing ; enters  
execution again.


In Nobles example "3.2. A Better FSM" FSM: defines <Fixed.Pt#> and  
thereafter compiles the list of execution tokens:

4 WIDE FSM: <Fixed.Pt#>   ( action# -- )
\            other   num    -     .      \ state
              DROP    (00)  (00)  (02)    \ 0
              DROP    (00)  DROP  (02)    \ 1
              DROP    (02)  DROP  DROP  ; \ 2


If you do not want to use that ]-trick, because it makes your program  
code more mysterious,  you archive the same result this way:

4 WIDE FSM: <Fixed.Pt#>   ( action# -- )
\              other       num        -        .         \ state
              ' DROP ,    ' (00) ,  ' (00) ,  ' (02) ,    \ 0
              ' DROP ,    ' (00) ,  ' DROP ,  ' (02) ,    \ 1
              ' DROP ,    ' (02) ,  ' DROP ,  ' DROP ,    \ 2

This way it is more obvious what comes into the array.


So the use of ] has nothing to do with the CREATE/DOES Part of  
creating a new defining word. ok?

Michael


(1) Finite State Machines in Forth; J. V. Noble
     http://dec.bournemouth.ac.uk/forth/jfar/index.html