created a new +FIELD name with an OFFSET-RT of offset. Then add the size value to the offset so that
the next /FIELD declaration will start at the end of the
field currently declared. This word is the simplest way to
declared structure access words in forth - the two STRUCT modules
contain a more elaborate series of words. This one is used like:
0 ( a fresh definition is started )
/CHAR /FIELD ->zapp.a ( zero offset from the base of the struct )
/CELL /FIELD ->zapp.b ( no alignment, starts off at 1 from base )
CONSTANT /zapp ( store size of complete zap structure )
/zapp ( extend the zap structure )
/CELL /FIELD ->zappx.c ( a new field )
CONSTANT /zappx ( and save it again )
CREATE zapp1 /zapp ALLOT ( a way to allocate a strucutre )
/zapp BUFFER: zapp2 ( another way to do it, semi-standard )
zapp2 ->zapp.b @ ( read a value from the field )
16 zapp2 ->zapp.b ! ( store a value in there )