successor ( str -- str' )

Vocabulary

successor

Inputs

str

a string

Outputs

str'

a string

Word description

Returns the successor to str. The successor is calculated by incrementing characters starting from the rightmost alphanumeric (or the rightmost character if there are no alphanumerics) in the string. Incrementing a digit always results in another digit, and incrementing a letter results in another letter of the same case.

If the increment generates a carry, the character to the left of it is incremented. This process repeats until there is no carry, adding an additional character if necessary.

Definition

USING: kernel math sequences successor.private ;

IN: successor

: successor ( str -- str' )
    dup empty? [
        dup [ alphanum? ] any? [
            reverse [ next-char ] map-until
            [ dup last suffix ] when reverse
        ] [ dup length 1 - over [ 1 + ] change-nth ] if
    ] unless ;