: _ ( a+1 len -- n f )
    OVER C@ ( a len c )
    '-' = IF
        1- SWAP 1+ SWAP ( a+1 len-1 ) _ 0 ROT ( f 0 n )
        - SWAP EXIT                    ( 0-n f )
    THEN ( a len )
    0 SWAP ( len ) 0 DO ( a r )
        OVER I + C@ ( a r c ) _pdacc ( a r f )
        IF DROP 1- 0 UNLOOP EXIT THEN LOOP ( a r )
    NIP 1 ;
: (parsed) ( a -- n f ) C@+ ( a+1 l ) _ ;