Re: Is there another way to define a regex?

[Nelo Onyiah]

Curious but are the non capturing groups necessary?
On 17 Jan 2016 11:35 p.m., "Tom Browder"  wrote:

> On Sun, Jan 17, 2016 at 3:03 PM, Moritz Lenz  wrote:
> > On 01/17/2016 06:07 PM, Tom Browder wrote:
> ...
> >> # regex of dirs to ignore
> >> my regex dirs {
> >>   \/home\/user\/\.cpan |
> >>   \/home\/tbrowde\/\.emacs
> >> }
> >
> > Better written as
> >
> > my regex dirs {
> >| '/home/user/.cpan'
> >| '/home/tbowde/.emacs'
> > }
> >
> > Yes, quoting does now work in regexes too. Cool, right? :-)
>
> Yes, very cool!  I have decided to use that format and it does ease
> adding or modifying entries.
>
> My final regex looks like this (shortened to only a couple of entries):
>
> my regex dirs {
>   ^
>   \s*
>   [# <= non-capture grouping
>| '/home/user/.cpan'
>| '/home/tbowde/.emacs'
># more entries...
>   ]
> }
>
> used like this:
>
>   next LINE if $line ~~ //;
>
> Thanks, Moritz!
>
> Best,
>
> -Tom
>

Re: Is there another way to define a regex?

[Gianni Ceccarelli]

On 2016-01-17 Tom Browder  wrote:
> My question: Is there a way to have Perl 6 do the required escaping
> for the regex programmatically, i.e., turn this:
> 
> my $str = '/home/usr/.cpan';
> 
> into this:
> 
> my regex dirs {
>   \/home\/usr\/\.cpan
> }
> 
> automatically?  

Yes! And it's also simpler than in Perl 5. I Perl 5, you would have to
do something like:

  my $dirs = qr{\Q$str};

but in Perl 6 you just do:

  my $dirs = regex { $str };

because the other behaviour, to interpret the contents of $str as
another regex to match, has more explicit syntax:

  regex { <$another_regex> }

For your initial use-case there is also another shortcut: an array is
interpreted as an alternation, so you could write:

  my @dirs = < /home/user/.cpan /home/tbrowde/.emacs >;
  my $regex = regex { @dirs };

and it would do what your Perl 5 example does.

If you want to be more restrictive, you can anchor the alternation:
  
  my $regex = regex { ^ @dirs };

Here is a complete program:

  use v6;

  my @dirs = < foo bar baz >;

  my $matcher = regex { ^ @dirs $ };

  for $*IN.lines -> $line {
  if $line ~~ $matcher {
  say "<$line> matched";
  }
  else {
  say "<$line> didn't match";
  }
  }

-- 
Dakkar - 
GPG public key fingerprint = A071 E618 DD2C 5901 9574
 6FE2 40EA 9883 7519 3F88
key id = 0x75193F88

To spot the expert, pick the one who predicts the job will take the
longest and cost the most.

Re: Workaround for Perl 5's __DATA__

[Tom Browder]

On Mon, Jan 18, 2016 at 6:47 AM, Kamil Kułaga  wrote:
> You may be happy with =finish block
...

Thanks, Kamil!

-Tom

'!' versus 'not' in boolean expression

[Tom Browder]

In creating some new Perl 6 programs I've run across several instances
I'm confused about, to wit:

Example 1
---

> my %h; say 'false' if !%h:exists;
Unexpected named parameter 'exists' passed

Example 2
---

> my %h; say 'false' if not %h:exists;
false

It looks like '!' doesn't work as I thought it was supposed to.  But,
I just discovered that when I use parens, it works.

Example 3
---

> my %h; say 'false' if !(%h:exists);
false

I presume the parens would cure the similar things I've noticed with
other classes.

When I look at the docs on Operators I see this:


prefix !

multi sub prefix:(Mu) returns Bool:D

Negated boolean context operator.

Coerces the argument to Bool by calling the Bool method on it, and
returns the negation of the result. Note that this collapses
Junctions.



prefix not

multi sub prefix:(Mu $x) returns Bool:D

Evaluates its argument in boolean context (and thus collapses
Junctions), and negates the result.


Those two definitions look very similar to my eyes, but I think the
subtle difference is intentional.But they are not identical.

Is there some rule of thumb here that a Perl 6 wannabe can grasp in
Perl 5 terms (e.g., prefer 'not' over '!')?  Or am I going to have to
go deep early into the object class structure?

Many thanks.

-Tom

Re: Workaround for Perl 5's __DATA__

[Kamil Kułaga]

You may be happy with =finish block

use v6;

say $=finish.split("\n").perl;


=finish
_
I like pancakes
And apples

On Sat, Jan 16, 2016 at 8:07 PM, Tom Browder  wrote:
> I have tried this in my Perl 6 code (v6.c):
>
> =begin DATA
> blah
> blah2
> =end DATA
>
> Then:
>
> for $=DATA.lines -> $line {
>   # process a line
> }
>
> but I get this message:
>
> Pod variable @=DATA not yet implemented. Sorry.
>
> Is there any workaround for this other than putting the data in an array?
>
> Thanks.
>
> Best regards,
>
> -Tom



-- 
Pozdrawiam

Kamil Kułaga

Re: '!' versus 'not' in boolean expression

[yary]

In Perl5, there's "&&" vs "and", "||" vs "or", "^" vs "xor", and "!"
vs "not", the difference being precedence. Perhaps it's the same with
Perl6...

Re: '!' versus 'not' in boolean expression

[Elizabeth Mattijsen]

> On 18 Jan 2016, at 19:55, Tom Browder  wrote:
> 
> In creating some new Perl 6 programs I've run across several instances
> I'm confused about, to wit:
> 
> Example 1
> ---
> 
>> my %h; say 'false' if !%h:exists;
> Unexpected named parameter 'exists’ passed

Yeah, this is an unexpected one.  However, there is a simple solution:

  my %h; say 'false' if %h:!exists;

In general, :foo is equivalent to foo => True, and :!foo is equivalent to foo 
=> False.


> Example 2
> ---
> 
>> my %h; say 'false' if not %h:exists;
> false
> 
> It looks like '!' doesn't work as I thought it was supposed to.  But,
> I just discovered that when I use parens, it works.

Yes, the ! binds closer, and eats the :exists, and then complains about it.



Liz

Re: '!' versus 'not' in boolean expression

[James Ellis Osborne III]

Too many Reimanns & Not enough role?

-jas

On 18 January 2016 at 11:37, Elizabeth Mattijsen  wrote:
>
>> On 18 Jan 2016, at 19:55, Tom Browder  wrote:
>>
>> In creating some new Perl 6 programs I've run across several instances
>> I'm confused about, to wit:
>>
>> Example 1
>> ---
>>
>>> my %h; say 'false' if !%h:exists;
>> Unexpected named parameter 'exists’ passed
>
> Yeah, this is an unexpected one.  However, there is a simple solution:
>
>   my %h; say 'false' if %h:!exists;
>
> In general, :foo is equivalent to foo => True, and :!foo is equivalent to foo 
> => False.
>
>
>> Example 2
>> ---
>>
>>> my %h; say 'false' if not %h:exists;
>> false
>>
>> It looks like '!' doesn't work as I thought it was supposed to.  But,
>> I just discovered that when I use parens, it works.
>
> Yes, the ! binds closer, and eats the :exists, and then complains about it.
>
>
>
> Liz

Re: '!' versus 'not' in boolean expression

[Tom Browder]

On Mon, Jan 18, 2016 at 1:37 PM, Elizabeth Mattijsen  wrote:
>> On 18 Jan 2016, at 19:55, Tom Browder  wrote:
>> In creating some new Perl 6 programs I've run across several instances
>> I'm confused about, to wit:
>>
>> Example 1
>> ---
>>
>>> my %h; say 'false' if !%h:exists;
>> Unexpected named parameter 'exists’ passed
>
> Yeah, this is an unexpected one.  However, there is a simple solution:
>
>   my %h; say 'false' if %h:!exists;
>
> In general, :foo is equivalent to foo => True, and :!foo is equivalent to foo 
> => False.

Okay, I'll just have to get used to it, then.

Thanks, Liz!

-Tom