: reader-loop ( -- )
    read1 [
        dup CHAR: \ = [
            drop read1
            { { CHAR: d [ CHAR: 0 10 random + write1 ] } } case
        ] [ write1 ] if
        reader-loop
    ] when* ;

: convert ( str -- str' )
    [ [ reader-loop ] with-string-writer ] with-string-reader ;