: eval (run '+) (left '0) -> (left  '1) (ran '+) ;
: eval (run '+) (left '1) -> (right '0) (ran '+) +carry eval ;

: +carry (left '0) -> (left  '1) (shift bits left) ;
: +carry (left '*) -> (left  '*) (shift bits left) ;
: +carry (left '1) -> (right '0) +carry ;



: eval (run '-) (left '1) -> (left  '0) (ran '-) eval ;
: eval (run '-) (left '0) -> (right '1) (ran '-) -carry eval ;

: -carry (left '0) -> (left '1) -carry ;
: -carry (left '1) -> (left '0) (shift bits left) ;
: -carry (left '*) -> (left '*) (shift bits left) ;



: eval (run '<) -> (ran '<) (shift bits right) eval ;

: (shift bits right) (left '*) -> (right '*) ;
: (shift bits right) (left ?bit) -> (right ?bit) (shift bits right) ;



: eval (run '>) (right '*) -> (left '*) (shift bits left) eval ;
: (shift bits left) (right '*) -> (right '*) ;
: (shift bits left) (right ?bit) -> (left ?bit) (shift bits left) ; 



: eval (run '[) (left "*00000000") ->
    (left "*00000000") (ran '[) (jump past matching bracket) ;
: eval (run '[) -> (ran '[) ;

: (jump past matching bracket) (balance '[) (run ']) ->
    (ran ']) (jump past matching bracket) ;
: (jump past matching bracket) (run '[) ->
    (ran '[) (balance '[) (jump past matching bracket) ;
: (jump past matching bracket) (run ']) ->
    (ran ']) eval ;



: eval (run ']) (left "*00000000") -> (left "*00000000") (ran ']) ;
: eval (run ']) -> (jump backwards to matching bracket) ;

: (jump backwards to matching bracket) (balance ']) (ran '[) ->
    (run '[) (jump backwards to matching bracket) ;
: (jump backwards to matching bracket) (ran ']) ->
    (run ']) (balance ']) (jump backwards to matching bracket) ;
: (jump backwards to matching bracket) (ran '[) ->
    (run '[) eval ;