How to change these small one-liners into Perl6 code?

[ABCXYZ]

I've just downloaded Rakudo, and changing my Perl5 code into Perl6, but I've encountered some difficulties:

1. print '218' =~ s/^18/3/r

2. $_ = '2316'; substr($_, -1, 1) = 8; print

3. map {$s+=int $_*($i=abs int 999/$_)*++$i/2 },(3,5,-15);print $s

4.

LOOP:
        say q/Please input a number (>1):/;
        while(<>){
                chomp;

                say $_;
                goto LOOP;
        }

How to make the above four scripts work in Perl6?

[moritz]

1:

print '218'.subst(rx/^18/, 3);

2: this is supposed to work with substr-rw, but doesn't with current rakudo.

3: Sorry, I don't even understand what this code does in Perl 5. Modifying and using a variable in the same statement is very detrimal for readability.

4: labels and goto aren't implemented in Rakudo. You can use prompt, or for lines() { } (since lines() is a lazy list, it doesn't read all the lines upfront; this was broken in some earlier Rakudo versions, but should be fine in the 2012-12 and possibly the 2012-11 releases).

I can recommend hanging out in the #perl6 IRC channel, we try to be helpful and friendly (and we succeed most of the time :-).

[ABCXYZ]

First, thank you very much.

>1: print '218'.subst(rx/^18/, 3);

Great, this works for me.
It was a real effort for me to figure out how "s///r" works in Perl6... It turned out to have a completely different syntax, but I do miss the Perl5's version: it's so concise, and since it is like a mother language, it can't be obfuscated anyway. I hope Perl6 can still allow the Perl5's sed syntax, conforming to TMTOWTDI. :-)

>2: this is supposed to work with substr-rw, but doesn't with current rakudo.

I see.

>3: Sorry, I don't even understand what this code does in Perl 5. Modifying and using a variable in the same statement is very detrimal for readability.

I will explain these code in the next post.

>4: labels and goto aren't implemented in Rakudo. You can use prompt, or for lines() { } (since lines() is a lazy list, it doesn't read all the lines upfront; this was broken in some earlier Rakudo versions, but should be fine in the 2012-12 and possibly the 2012-11 releases).

I am using version 2012-11, and it is slurping. but I wonder is the parentheses with "lines()" mandatory? It doesn't seem like Perl's style though?

>I can recommend hanging out in the #perl6 IRC channel, we try to be helpful and friendly (and we succeed most of the time :-).

I will try that.

[ABCXYZ]

I was simply translating my Perl5 one-liners on ProjectEuler into Perl6's code.

These are all on its first problem:


If we list all the natural numbers below 10 that are multiples of 3 or
+ 5, we get 3, 5, 6 and 9. The sum of these multiples is 23.

Find the sum of all the multiples of 3 or 5 below 1000.

(I generalized this to: 
   below 10**$n for code #1 and #2, 
or below $N for code #3)

This is my fastest solution in Perl5: (not in the code #1..4 above)
perl5 -e '$n=3;print 2,3x--$n,1 .6x$n+2'

The following is the origin of code #1, which works beyond the limit of 64 bit int, since it uses string op:
$n=3;print 2,(3x--$n.1 .6x--$n.8)=~s/^18/3/r

This is the origin of code #2:
$n=3;$_=2 .3x--$n.1 .6x$n;substr($_,-1)+=2;print

So code #3 is a more general solution for $N which is typically not an integer exponentiation of 10:
map{$s+=int$_*($i=abs int 999/$_)*++$i/2}(3,5,-15);print$s

They all give the same result: 233168 for $n=3, but work for other $n as well.

[raiph]

https://github.com/perl6/perl6-examples/tree/master/euler should interest you.

Five solutions have been added to this repo over the last 4 years. The latest one was added 18 days ago:

say [+] grep * %% (3|5), ^1000;

This means "say the sum of numbers that are divisible by 3 or 5 in the range zero up to (but not including) 1000".

[ABCXYZ]

I've made #4 work finally:

while prompt qq/Please input a number (>1):\n/ -> $_ {
                say $_;
        }

A lot of unexpected things:


1. For some reason, Rakudo does not recognize the "LOOP:" construct, I just can't use "goto LOOP" to jump to a label.

2. The simple "while(<>){}" idiom doesn't work anymore. Though I've heard that "for =<> {}" is one alternative, but it seems that Rakudo doesn't support it yet.

3. The compiler suggest me to use "lines()" instead of "while(<>)", but "lines()" slurps all the input, so I can't input line by line, luckily there is a "prompt" function instead.

4. Since "while(<>){}" does not work, the implicit variable is not assigned, so I have to explicitly assign it by: "-> $_".

5. For some reason, bare function "chomp" and "say" does not work any more, I have to pass the parameter "$_" explicitly.

6. But the chomp function is not necessary anymore, the NL is automatically chomped. This sounds like the "perl5 -l" option, I guess we will need a "perl6 -L" option to do the inverse in the future?


I am surprised that Perl6 is so much different from Perl5.
But the code does become much shorter and clearer, at least from this example.

[LanX]

> 1. For some reason, Rakudo does not recognize the "LOOP:" construct, I just can't use "goto LOOP" to jump to a label.

loop is a control keyword in perl6 replacing c-style For Loops, IIRC to avoid the confusion with Foreach Loops.

You can't use a keyword as a label.

[ABCXYZ]

>> 1. For some reason, Rakudo does not recognize the "LOOP:" construct, I just can't use "goto LOOP" to jump to a label.

>loop is a control keyword in perl6 replacing c-style For Loops, IIRC to avoid the confusion with Foreach Loops.
>You can't use a keyword as a label.


But I was using "LOOP:" instead of "loop", the interpreter should have distinguished them.