( Drop RSP until I-2 == INTERPRET. )
: EXIT!
['] INTERPRET ( I )
BEGIN ( I )
DUP ( I I )
R> DROP I 2- @ ( I I a )
= UNTIL
DROP
;
( a -- a+1 c )
: C@+ DUP C@ SWAP 1+ SWAP ;
( c a -- a+1 )
: C!+ SWAP OVER C! 1+ ;