loop iterator in a string

Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:

Dear Monks,
I would like to use the ".." as a loop operator but in a string. Is there any simple perl-ish way I can accomplish this? For some reason, I thought perl would support this, but it doesn't.

my $arr=[1,2,3,4,5,6,7];
my $loop="2,4..5";
splice @$arr,$_,0,999 foreach($loop);
[download]

I want $arr to be [1, 2, 999, 3, 999, 999, 4, 5, 6, 7]. This works fine if you pass in 2,4..5 instead of "2,4..5". I notice that '2', '4'..'5' will also work, but when the .. operator is within string, it does not.

Thank you for your time!

Michael

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Re: loop iterator in a string by haukex (Archbishop) on Sep 27, 2021 at 18:46 UTC
If you don't mind using a dash instead of two dots, you might be interested in Set::IntSpan. See the example of its `next` method in the Synopsis for how to interate through the set. Just don't use the indirect object syntax as it is shown in the documentation, i.e. write `Set::IntSpan->new` instead of `new Set::IntSpan`, use `$set->insert($n)` instead of `insert $set $n`, and so on.	[reply] [d/l] [select]
Re^2: loop iterator in a string by Anonymous Monk on Sep 28, 2021 at 13:20 UTC
I absolutely love this idea. Thank you for the suggestion!	[reply]
Re: loop iterator in a string by tybalt89 (Monsignor) on Sep 27, 2021 at 21:39 UTC
For the evalphobic... #!/usr/bin/perl use strict; # https://perlmonks.org/?node_id=11137057 use warnings; my $arr=[1,2,3,4,5,6,7]; my $loop="2,4..5"; splice @$arr,$_,0,999 foreach map { /\.\./ ? $` .. $' : $_ } split /,/ +, $loop; use Data::Dump 'dd'; dd $arr; [download] Outputs: `[1, 2, 999, 3, 999, 999, 4 .. 7]` [download]	[reply] [d/l] [select]
Re: loop iterator in a string by LanX (Saint) on Sep 27, 2021 at 18:33 UTC
the "simple" way is using `eval` `DB<53> say for eval "2,4..9" 2 4 5 6 7 8 9` [download] NB: this might lead to problems with large intervals though, because foreach can't tell when to iterate lazily. But good enough if you don't intend to scale large. Cheers Rolf _{(addicted to the Perl Programming Language :) Wikisyntax for the Monastery}	[reply] [d/l]
Re^2: loop iterator in a string by Anonymous Monk on Sep 27, 2021 at 18:41 UTC
Oh that's brilliant Rolf! I totally forgot about eval. This is definitely good enough for my use case. Thank you!	[reply]
Re^3: loop iterator in a string by haukex (Archbishop) on Sep 27, 2021 at 18:54 UTC
Please be aware that eval with anything other than a fixed, literal string (i.e. no variables interpolated in) has the potential to introduce security issues or other subtle bugs.	[reply]
Re^4: loop iterator in a string by LanX (Saint) on Sep 27, 2021 at 21:12 UTC
Re^5: loop iterator in a string by haukex (Archbishop) on Sep 28, 2021 at 10:23 UTC
Some notes below your chosen depth have not been shown here
Re: loop iterator in a string by BillKSmith (Monsignor) on Sep 27, 2021 at 18:49 UTC
This is pretty close to what you want. Use eval to evaluate the operators in the string. `use strict; use warnings; my $arr=[1,2,3,4,5,6,7]; my $loop="2,4..5"; splice @$arr,$_,0,999 foreach(eval $loop); $, = ' '; print @$arr` [download] OUTPUT: `1 2 999 3 999 999 4 5 6 7` [download] Bill	[reply] [d/l] [select]
Re: loop iterator in a string by LanX (Saint) on Sep 28, 2021 at 15:45 UTC
> I would like to use the ".." as a loop operator but in a string. Does it really need to be a string? What about a functional solution to store intervals? `DB<83> $loop = sub {2,4..5} DB<84> say for &$loop 2 4 5 DB<85>` [download] Cheers Rolf _{(addicted to the Perl Programming Language :) Wikisyntax for the Monastery}	[reply] [d/l]

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