Beefy Boxes and Bandwidth Generously Provided by pair Networks
Pathologically Eclectic Rubbish Lister
 
PerlMonks  

Re^4: check for square-number with a regex

by spx2 (Chaplain)
on Oct 24, 2009 at 09:56 UTC ( #803019=note: print w/ replies, xml ) Need Help??


in reply to Re^3: check for square-number with a regex
in thread check for square-number with a regex

I think you're aware of this solution for anbncn but I'll post it anyway(it uses ??{} blocks and ?{} and is a Perl regex).

$r = qr/^(a+b)(?{ $a = -1+length $^N; })(??{ $b=$a-1;"(b{$b})" })(??{ +"(c{$a})" })/x; sub test { print $_[0] =~ $r ? "matched\n" : "not matched\n"; } test "aaabbbccc"; test "aaaabbbccc"; test "aaaabbbbccc"; test "aaaabbbbcccc"; test "aabbbbcccc"; test "abc"; test "aabbcc";
Result on Perl v5.8.8:
matched not matched not matched matched not matched matched matched


Comment on Re^4: check for square-number with a regex
Select or Download Code
Replies are listed 'Best First'.
Re^5: check for square-number with a regex
by JavaFan (Canon) on Oct 24, 2009 at 11:54 UTC
    I (and others in this thread) explicitely mentioned no using (?{}) and (??{}). Allowing those means you have the full power of Perl available. It would mean that anything you can do in Perl, you can to with a "regular expression", and the question "can I do foo with a regular expression" becomes a non-question.

    And I would have used (?{}) differently anyway. Something like:

    /^(a+)(b+)(c+)$(?(?{length($1) == length($2) && length($2) == length($ +3)})|(*FAIL))/;
    But that's just a fancy way of writing:
    /^(a+)(b+)(c+)$/ && length($1) == length($2) && length($2) == length($ +3);
    And you can solve the "match a square" with:
    /^([0-9]+)$(?(?{sqrt($1) == int sqrt($1)})|(*FAIL))/;
    Or in general, match "whatever" by:
    /^(.*)$(?(?{is_whatever($1)})|(*FAIL))/;
    after writing the appropriate "is_whatever" function.

    But that means the question no longer is "how can I do foo with a regexp", but "how can I do foo in Perl".

Log In?
Username:
Password:

What's my password?
Create A New User
Node Status?
node history
Node Type: note [id://803019]
help
Chatterbox?
and the web crawler heard nothing...

How do I use this? | Other CB clients
Other Users?
Others having an uproarious good time at the Monastery: (10)
As of 2015-07-30 12:45 GMT
Sections?
Information?
Find Nodes?
Leftovers?
    Voting Booth?

    The top three priorities of my open tasks are (in descending order of likelihood to be worked on) ...









    Results (271 votes), past polls