5 - Forth Interest Group

if r> compl \ Lengths match ... try comparison
else
endif
4drop r>drop 1 \ Show mismatch
\ Advance to next item past the current counted string.
\ seg:addr points to counted string. Takes into account
\ trailing integer.
: nextstr ( seg addr -- seg addr' )
countl + 2+
\ Search one of the temporary segments.
\ seg1:addrl points to string to search for
\ seg2 is temporary segment to search
\ max is maximum current offset in segment.
\ n is returned associated integer; -1 means
\ the string was not located.
: search-tseg ( segl addrl seg2 max -- n )
dup \ Anything to look for?
if
> r \ Save max
0 \ Start search at zero
begin
2over 2over \ Dup seg/address
ccompl \ Look for match
0 =
if 2swap r> 3drop \ Clear stack
count1 + @1 \ Fetch value
exit
endif
nextstr \ Advance to next string
dup r@ >= \ Topped out?
until
r>drop \ Clear return stack
endif
4drop \ Clear stack
- 1 \ Show error
\ **
\ ** Instance variable segment handling
\ **
\ The ivar segment is a temporary region where the system
\ keeps a list of the current class definition's instance
\ variables. Each entry is composed of a length byte, the
\ name, and a 2-byte value that indicates that instance
\ variable's offset into an instance of the class
\ Allocate space for the IVAR segment. Place the segment
\ in global variable ivar-seg
: alloc-ivar-seg ( -- )
IVAR-SEG-SIZE alloc
error \ Fetch error
if abort" Ivar allocation error"
endif
ivar-seg ! \ Save pointer
\ Clear the ivar segment
: clear-ivar-seg ( -- )
0 ivar-next !
I
Forth Dimensions 11
(Zisting continues
lethod by mimicking the
m-time action of the colon
rord. You pass (domethd)
the starting address of
le method code and it
andles the rest.
PCYerk does not create
andard Forth headers (5 la
reate) for instance varibles
and methods. In the
ase of instance variables,
ou want their names to disppear
after the class definion.
For method names, you
on't want their names taklg
up header space, since
ley are instantly resolved to
wo-byte selector ID numers.
PCYerk allocates two
nemory blocks (using the
JDForthwordalloc, which
brovides access to the DOS
unction for allocating a
nemory segment): one to
!old instance variable names,
he other to hold method
lames. Each name stored in
me of these blocks is associ-
~ted with an integer.
In the case of instance
rariables, the associated ineger
carries that instance
rariable's offset into the
~bject's local data space. At
:ompile time, whenthe sysem
encounters an instance
rariable, it looks up the
rariable's offset and com-
3iles that as a literal, folowed
by the word ( iva r ) .
4t run time, ( ivar ) takes the
~ffset from the stack and
resolves that offset to an adkss.
In the case of methods,
he associated integer is the
selector ID number. When
you define a new method's
name, the system increments
an internal counter and the
incremented value becomes
that method's ID number.
This ensures a unique ID
number for each method.
(Yerkused a hashing method
to generate such ID numbers.
I chose a separate route,
since the code for handling
instance variable names and
method names was so similar.)
But wait. If the system
puts method names and in-
January 1992 February