Paste: A different approach to successor

USING: kernel combinators.short-circuit sequences ;
IN: successor

! Throughout, ?? reads as follows: f means not in range, 0 for in
! range and 1 for at end of range.

: in-range? ( elt min max -- ? )
    [ over ] dip [ >= ] [ <= ] 2bi* and ;

: where-in-range? ( elt min max -- ?? )
    [ nip = 1 and ] [ in-range? 0 and ] 3bi or ;

: inc-able? ( elt -- ?? )
    { [ CHAR: a CHAR: z where-in-range? ]
      [ CHAR: A CHAR: Z where-in-range? ]
      [ CHAR: 0 CHAR: 9 where-in-range? ] } 1|| ;

: carry ( elt -- elt' )
    { { CHAR: z [ CHAR: a ] }
      { CHAR: Z [ CHAR: A ] }
      { CHAR: 9 [ CHAR: 0 ] }
      [ "Aargh." throw ]
    } case ;

: map-carry ( seq -- seq' )
    [ dup inc-able? [ carry ] when ] map ;

: split-carry ( seq -- before elt/f after )
    dup [ inc-able? 0 = ] find-last dup
    [ [ cut-slice rest-slice ] dip swap ]
    [ 2drop [ f f ] dip ] if ;

: successor ( seq -- seq' )
    split-carry [ [ 1 + suffix ] when* ] dip map-carry append >string ;