From mark at purdue.edu  Mon Jun 11 04:57:53 2018
From: mark at purdue.edu (Mark Senn)
Date: Mon, 11 Jun 2018 07:57:53 -0400
Subject: [Purdue-pm] Perl 6 get primes
Message-ID: <4739.1528718273@pier.ecn.purdue.edu>

From
    https://twitter.com/nogoodnickleft/status/1001477056985747456
here is how to get the first 1000 primes in Perl 6:
    (1..*).grep(&is-prime).head(1000);

I read this to myself as
    For 1 to whatever if the number is prime save it to
    a list and use the first 1000 primes on that list.

NOTE: The is-prime routine reportedly uses the Miller-Rabin primality
test which relies on the unproven extended Riemann hypothesis.

Perl6 computes these in a lazy fashion so they are only computed as they
are used (you can also read this is "as they are needed").  The idea is
don't take the time to compute all of them and then use use one or more
of them at a time---instead compute the ones you need, use them, compute
more, use those, etc.

-mark

From mark at purdue.edu  Wed Jun 13 07:17:05 2018
From: mark at purdue.edu (Mark Senn)
Date: Wed, 13 Jun 2018 10:17:05 -0400
Subject: [Purdue-pm] Perl 6 regexes
Message-ID: <43045.1528899425@pier.ecn.purdue.edu>

Perl 5 has regular expressions that can be used to match character
strings.  These have been MUCH improved and are known as regexes in Perl 6.

Below is a message I sent to the Perl6 users mailing list about how to
remove leading zeros.  Thought you might be interested in it, especially
how to use name captures in the last example.


To: Norman Gaywood <ngaywood at une.edu.au>
cc: perl6-users <perl6-users at perl.org>
Subject: Re: How do I remove leading zeros?
Date: Wed, 13 Jun 2018 10:02:43 -0400
From: Mark Senn <mark at pier.ecn.purdue.edu>

If $x is set to "01.02.03"

(Not using normal message quoting to make message shorter.
[1] ToddAndMargo    [2] Norman Gaywood    [3] Mark Senn)

DOING         $x ~~ s:global/"0"(\d)/ $0 /;                              [1]
SETS $x TO    "1 . 2 . 3"                                                [1]
COMMENT       Spaces on right hand side of s command are significant.    [2]

DOING         $x ~~ s:global/"0"(\d)/$0/;                                [2]
SETS $x to    "1.2.3"                                                    [2]
COMMENT       Zeroes would de deleted from "101.102.103".                [3]

(I suspect the general case is delete leading zeroes or zeroes
immediately following periods.)

DOING         $x ~~ s:g/(^|".")0+/$0/;                                   [3]
              or, using named captures,
              $x ~~ s:g/$<leader>=(^|".")0+/$<leader>/;
SETS $x to    "1.2.3"                                                    [3]
COMMENT       Zeroes would not be deleted from "101.102.103".            [3]

For me, the last solution is the clearest: replace all beginning of
strings or "."  followed by one or more zeroes by the beginning of the
string or ".", whichever was matched.

-mark