sp@ ( – addr )
returns the address corresponding to the top of data stack.
rp@ ( – addr )
returns the address corresponding to the top of return stack.
sp! ( addr – )
sets the stack pointer to addr, thus restoring the stack depth to
the same depth that existed just before addr was acquired by
executing sp@.
rp! ( addr – )
sets the return stack pointer to addr. thus restoring the return
stack depth to the same depth that existed just before addr was
acquired by executing rp@.
Legend:
variable handler \ Most recent exception handler \ Put catchframe on return stack. \ v v : CATCH ( xt -- exc# | 0 ) ( 1) ( 2) sp@ >r ( -- xt) ( RS: -- sp ) ( 3) handler @ >r ( -- xt) ( RS: -- sp hlr ) ( 4) rp@ handler ! ( -- xt) ( RS: -- sp hlr ) ( 5) execute ( -- ) ( RS: -- sp hlr ) ( 6) r> handler ! ( -- ) ( RS: -- sp ) ( 7) r> drop ( -- ) ( RS: -- ) ( 8) 0 ( -- 0 ) ( 9) ;
sp
, hlr
and handler
are current catchframe now.\ TROW exits to saved context if exc# <> 0 : THROW ( i*x exc# -- i*x exc# | i*x exc# ) ( RS: -- sp hlr i*adr ) ( 1) dup 0= ( -- i*x exc# f ) ( RS: -- sp hlr i*adr ) ( 2) if drop exit then ( -- i*x ) ( RS: -- sp hlr i*adr ) ( 3) handler @ rp! ( -- i*x exc# ) ( RS: -- sp hlr ) ( 4) r> handler ! ( -- i*x exc# ) ( RS: -- sp ) ( 5) r> ( -- i*x exc# sp ) ( RS: -- ) ( 6) swap ( -- i*x sp exc# ) ( RS: -- ) ( 7) >r ( -- i*x sp ) ( RS: -- exc# ) ( 8) sp! ( -- xt ) ( RS: -- exc# ) ( 9) drop r> ( -- exc# ) ( RS: -- ) ( 10) ;
throw
expects an exception numer on the stack, passing or dropping it, and its returnstack picture has a catchframe underneath the current returnaddresses.\ enable "spam" to THROW an exeption number in case of exeption. : spam ( -- ) ... #exc THROW ; \ put "spam" into exception handling frame using CATCH : sapm-exc ( i*x -- ) ... ['] spam CATCH ( -- #exc ) dup 0= IF drop exit then \ = NOOP dup #exc = IF ... \ known error code, do execption handling else ... throw \ unknown error code; re-throw system code then ;
( finis)