title: STRUCTURES, very simple
description:
<forthspan>
 : ^FIELD CREATE , DOES> @ + ; ( offset "name" -- offset )
                               ( name: addr -- addr+offset )

 \ base stricture
 0
   ^FIELD mst^x CELL+
   ^FILED mst^y CELL+
   ^FIELD mst^a CHAR+
   ^FIELD mst^b CHAR+ ALIGNED
   ^FILED mst^z CELL+
 CONSTANT mst-size    \ mst for "My STructure"

 \ derived structure
 mst-size
   ^FIELD mst^u CELL+
   ^FIELD mst^v CELL+
 CONSTANT xmst-size

: foo
	...
	( addr ) mst^x @ ( val )
	...
	( val addr ) mst^y !
;

</forthspan>

More-complex:
<forthspan>
 : @FIELD CREATE ,         ( offset "name" -- offset )
          DOES> @ + @ ;    ( name: addr -- val )
 : !FIELD CREATE ,         ( offset "name" -- offset )
          DOES> @ + ! ;    ( name: val addr -- )
 : C@FIELD CREATE ,        ( offset "name" -- offset )
          DOES> @ + @ ;    ( name: addr -- val )
 : C!FIELD CREATE ,        ( offset "name" -- offset )
          DOES> @ + ! ;    ( name: val addr -- )

0
 ^FIELD xyz^c C@FIELD xyz.c C!FIELD xyz!c CHAR+ ALIGNED
 ^FIELD xyz^x  @FIELD xyz.x  !FIELD xyz!x CELL+
CONSTANT /xyz
\ Slash "/" stands for "size-of"

</forthspan>
or
<forthspan>
: word: ^FIELD @FIELD !FIELD CELL+ ;
: byte: ^FIELD C@FIELD C!FIELD CHAR+ ;

0
 word: smp^x smp.x smp!x
 byte: smp^a smp.a smp!a
 byte: smp^b smp.b smp!b
 ALIGNED
 word: smp^z smp.z smp!z
CONSTANT /smp
</forthspan>

Explanation:
 to be written

Page-written-by:
 mlg

Notes:
 GuidoD most likely would say that ^FIELD should be called +FIELD
 and that the field selectors must be of the form ->structname.fieldname
 rather than structname[operation]fieldname . It's a matter of taste.

 Anyway, to add structures to Forth you need one line of auxiliary code.

guidod-comment:
 to give you an idea of the look with using +FIELD to declare an
 offset-constant, here is an example

<forthspan>
 0
 +field my.x+ cell+
 +field my.y+ cell+
 +field my.a+ char+
 +field my.a+ char+
 aligned
 +field my.z+ cell+
 +field my+ drop

 0 my+ buffer: my.buf
 42 my.buf my.z+ !

 0 my+ \ extends
 +field other.w+ cell+
 +field other+ drop
</forthspan>

 note that only a single word +FIELD is needed to build a complete
 series of structure accessors and declarators. Since the words CHAR+
 and CELL+ are part of the ANS Forth standard, no other word is needed
 unlike the case of /FIELD where the usual but not-required words
 /CELL and /CHAR would be needed, as this:

<forthspan>
 0
 /cell /field ->my.x
 /cell /field ->my.y
 /char /field ->my.a
 /char /field ->my.b
 aligned
 /cell /field ->my.z
 constant /my

 /my buffer: my.buf
 42 my.buf ->my.z !

 /my \ extends
 /cell /field ->other.w
 constant /other
</forthspan>

however the latter is a bit more readable and has references in
the openboot standard where the simplefield declarator was just
called FIELD (which some forth system tooks for another meaning).