Regexp bug?

From: Ian Wild <ian.wild_at_eurocontrol.be>
Date: Fri, 28 May 1999 09:58:16 +0200

Is there some weirdness involved in the interaction
between parens and the '?' operator? It looks as
if an optional parenthesised group can vanish completely
from the results. Here's an example of what I mean:

Welcome to the STk interpreter version 3.99.4 [Linux-2.X-ix86]
Copyright © 1993-1999 Erick Gallesio - I3S - CNRS / ESSI <eg_at_unice.fr>

STk> (define re (string->regexp "^(xx)?(A*)$"))
re

; Now, as I understand it, re should always return either
; #f or a list of three elements

STk> (re "ZZZ")
#f
; good

STk> (re "x")
#f
; good

STk> (re "xx")
((0 2) (0 2) (2 2))
; very good

STk> (re "xxAAA")
((0 5) (0 2) (2 5))
; very very good

STk> (re "A")
((0 1))
; eek!
Received on Fri May 28 1999 - 09:59:10 CEST