Regex Question

[johnd]

How does newLISP control the value of system variables in regex?  It seems they are set only on non-nil regex results.



> (regex ".*([aeiou]{2}).*" "Seattle")

("Seattle" 0 7 "ea" 1 2)

> $1

"ea"

> (regex ".*([aeiou]{2}).*" "San Francisco")

nil

> $1

"ea"

>



If this is the intended behavior it should probably be documented.  I would argue that nil is a result and that $1 should return nil when the regex evaluates to nil.  This was an issue recently because I was checking for $1 to be nil rather than the regex expression itself.  The regex evaluated to nil but $1 retained a previous value.



John

[/i]

[cormullion]

Is this the same problem as I had?



http://www.alh.net/newlisp/phpbb/viewtopic.php?t=1948">//http://www.alh.net/newlisp/phpbb/viewtopic.php?t=1948

[Jeff]

I disagree.  I've put that side effect to good use in progressive logic.  You can set $0 yourself between regexes.  And you should always check the return value :)