At 08:25 AM 6/7/2001 -0700, Martin Weinless wrote:
>take the regexp '.n+..?.?v*.'
>
>By all that is sacred, if we use the string 'supernova', there should be
>no match since there are too many characters before the 'n'
>
>However, any regexp checking code will report a match.
Atom by atom:
. - match a character. Will match the 's' to begin with.
n+ - match 'n' one or more times. Since the second character isn't a 'n''
it has to advance the pointer until the . matches the 'r'.
. - match a character. Matches 'o'.
.? - match a character 0 or 1 times. Will match 'v' to begin with (greedy).
.? - match a character 0 or 1 times. Will match 'a' to begin with.
v* - match 'v' 0 or more times. We're at the end of the string initially,
so we match none.
. - match a characer. Oops, there aren't any. Never mind, we have some
backtracking we can try. First one is to take that last .? and match 0
instead of 1 character. Now the v* matches 0 characters and the final .
matches the 'a'. Success!
