Hi Richard, I'm not able to come to the same conclusions.
Specifically, the previous code examples starting with 'for lines()'
always have to have parentheses following 'lines' (as in 'lines()
{...}'), otherwise Perl_6 balks (examples 6 and 7 previously posted).
This is whether 'information is being passed' or not (i.e. empty
parentheses are required):
#example 6:
mbook:~ homedir$ perl6 -e ' for lines() { say .split(":")[0, 2, 1,
5].join("\t") };' six_fruits1.txt
apple carrot banana favabean
apricot cabbage basil fennel
acai celery beets figs
#example 6 no-parens:
mbook:~ homedir$ perl6 -e ' for lines { say .split(":")[0, 2, 1,
5].join("\t") };' six_fruits1.txt
===SORRY!===
Function 'lines' needs parens to avoid gobbling block
at -e:1
------> say .split(":")[0, 2, 1, 5].join("\t") };
Missing block (apparently claimed by 'lines')
at -e:1
------> say .split(":")[0, 2, 1, 5].join("\t") };
#example 7:
mbook:~ homedir$ perl6 -e 'for lines() {.split(":")[0, 2, 1,
5].join("\t").say};' six_fruits1.txt
apple carrot banana favabean
apricot cabbage basil fennel
acai celery beets figs
#example 7 no-parens:
mbook:~ homedir$ perl6 -e 'for lines {.split(":")[0, 2, 1,
5].join("\t").say};' six_fruits1.txt
===SORRY!===
Function 'lines' needs parens to avoid gobbling block
at -e:1
------> {.split(":")[0, 2, 1, 5].join("\t").say};
Missing block (apparently claimed by 'lines')
at -e:1
------> {.split(":")[0, 2, 1, 5].join("\t").say};
mbook:~ homedir$ perl6 --version
This is Rakudo version 2019.07.1 built on MoarVM version 2019.07.1
implementing Perl 6.d.
mbook:~ homedir$
Other Perl_6 users have replied with a general discussion of
differences between using lines() as a method, or in a subroutine. I
still have to review some of those comments. However, as I'm using the
latest Perl_6 version (2019.07.1), I'm fairly confident in the results
above (and below).
Also, the examples below show that 'for lines[0..2] {...}' works,
despite the previous error message insisting on parentheses ("Function
'lines' needs parens to avoid gobbling block at -e:1"). Taken
together, the results above and below seem to indicate to me that the
use of a bare 'lines' sub is disallowed, at least in a 'for' loop.
--Best Regards, Bill.
#example 10:
mbook:~ homedir$ perl6 -e 'for lines { say .split(":")[0, 2, 1,
5].join("\t") };' six_fruits1.txt
===SORRY!===
Function 'lines' needs parens to avoid gobbling block
at -e:1
------> say .split(":")[0, 2, 1, 5].join("\t") };
Missing block (apparently claimed by 'lines')
at -e:1
------> say .split(":")[0, 2, 1, 5].join("\t") };
#example 11:
mbook:~ homedir$ perl6 -e 'for lines() { say .split(":")[0, 2, 1,
5].join("\t") };' six_fruits1.txt
apple carrot banana favabean
apricot cabbage basil fennel
acai celery beets figs
#example 12:
mbook:~ homedir$ perl6 -e 'for lines[0..2] { say .split(":")[0, 2, 1,
5].join("\t") };' six_fruits1.txt
apple carrot banana favabean
apricot cabbage basil fennel
acai celery beets figs
On Fri, Aug 2, 2019 at 1:20 AM Richard Hainsworth
<rnhainswo...@gmail.com> wrote:
>
> Not quite sure what sort of "rule" you want.
>
> You used () and [] which do different things and the results were exactly
> what I would expect. They are covered in the documentation. Basically, ()
> without a space, eg xxxx() not xxxx (), is used to pass information to the
> sub or method xxxx.
> If no information is being passed, then no need to use (). The way xxxx
> responds to no data provided depends on the way xxxx is written. The
> programmer could provide default values for the arguments it expects. Perl6
> also makes the value of the default variable, eg $_, to xxxx.
> If you put a space between xxxx (), then () is interpreted as an empty list
> and provide to xxxx as a single piece of information.
> [] Are used to dereference a list (sequence or array, they are all slightly
> different).
>
> I'll comment more below. Sometimes I think through the process using slightly
> different and less exact words. My comments are illustrative.
>
> On Fri, 2 Aug 2019, 04:50 William Michels, <w...@caa.columbia.edu> wrote:
>>
>> Hi Richard, I'm trying to figure out when the parentheses in 'lines()'
>> can be dropped, and 'lines' used instead. Any pointers? I have about
>> nine or so working examples below, but formulating a clear
>> rule-of-thumb is proving elusive. Any help appreciated, --Best, Bill.
>>
>> # test file: six_fruits1.txt
>> mbook:~ homedir$ cat six_fruits1.txt
>> apple:banana:carrot:dragonfruit:eggplant:favabean
>> apricot:basil:cabbage:dill:escarole:fennel
>> acai:beets:celery:daikon:endive:figs
>>
>> mbook:~ homedir$ perl6 -e '.say for lines()' six_fruits1.txt
>> apple:banana:carrot:dragonfruit:eggplant:favabean
>> apricot:basil:cabbage:dill:escarole:fennel
>> acai:beets:celery:daikon:endive:figs
>
> Here 'lines ()' is the same as 'lines'.
> The program in the string after -e is provided with the data inside the file.
>>
>>
>> mbook:~ homedir$ perl6 -e '.say for lines' six_fruits1.txt
>> apple:banana:carrot:dragonfruit:eggplant:favabean
>> apricot:basil:cabbage:dill:escarole:fennel
>> acai:beets:celery:daikon:endive:figs
>
> The top two are equivalent
>>
>>
>> mbook:~ homedir$ perl6 -e '.say for lines("a\nb\n")' six_fruits1.txt
>> a
>> b
>
> Here you provided data to 'lines' which it was able to interpret as a set of
> lines. So it printed them. The data in six_fruits is ignored because you
> provided the data explicitly.
>>
>>
>> mbook:~ homedir$ perl6 -e '.say for lines[0]' six_fruits1.txt
>> apple:banana:carrot:dragonfruit:eggplant:favabean
>
> Six_fruits has 3 lines. Lines has processed the data. But you wrote '[0]'
> which extracted the first line, and that was processed by the 'for' loop. In
> other words the 'for' was only given one piece of information to process.
>>
>>
>> mbook:~ homedir$ perl6 -e '.say for lines[0..1]' six_fruits1.txt
>> apple:banana:carrot:dragonfruit:eggplant:favabean
>> apricot:basil:cabbage:dill:escarole:fennel
>
> The '[0..1]' extracts the first three pieces of data from 'lines' and they
> are processed by the 'for'
>>
>>
>> mbook:~ homedir$ perl6 -e ' for lines() { say .split(":")[0, 2, 1,
>> 5].join("\t") };' six_fruits1.txt
>> apple carrot banana favabean
>> apricot cabbage basil fennel
>> acai celery beets figs
>
> Could be just 'lines', which provides a list of the lines in the file to the
> 'for'
> Inside the 'for' the data is in the topic or default variable. You could
> access it as $_ but '.split' accesses it automatically. Split generates
> another list. '[0,2,1,5]' extracts the relevant elements of the list and
> generates another list which is passed to the'join'. The output from join is
> passed to 'say' which is written in sub form. Sub form means you write the
> name of the sub first, then you write where the data is coming from.
>
>>
>> mbook:~ homedir$ perl6 -e ' for lines() {.split(":")[0, 2, 1,
>> 5].join("\t").say};' six_fruits1.txt
>> apple carrot banana favabean
>> apricot cabbage basil fennel
>> acai celery beets figs
>
> Exactly the same for perl6 as before except that 'say' is written in sub form
> above and in method form here. Method form means you can append the 'say' to
> a chain of processing units.
>>
>>
>> mbook:~ homedir$ perl6 -e 'for "six_fruits1.txt".IO.lines()
>> {.split(/\:/)[0, 2, 1, 5].join("\t").say};'
>> apple carrot banana favabean
>> apricot cabbage basil fennel
>> acai celery beets figs
>
> Here just accessing the data in the file explicitly in perl6.
>>
>>
>> mbook:~ homedir$ perl6 -e 'for "six_fruits1.txt".IO.lines
>> {.split(/\:/)[0, 2, 1, 5].join("\t").say};'
>> apple carrot banana favabean
>> apricot cabbage basil fennel
>> acai celery beets figs
>
> Same as above. No () on lines
>>
>>
>>
>>
>>
>> On Mon, Jul 29, 2019 at 1:07 AM Richard Hainsworth
>> <rnhainswo...@gmail.com> wrote:
>> >
>> > Also no need for all the brackets
>> >
>> > .say for lines;
>> >
>> > This is quite idiomatic Perl 6 and not golfing
>> >
>> > On Mon, 29 Jul 2019, 07:13 Joseph Brenner, <doom...@gmail.com> wrote:
>> >>
>> >> > Hmmm. I would expect that to be in the Perl 5 to Perl 6 Migration
>> >> > Guides, but I do not see it there.
>> >>
>> >> Exactly, I was just looking there, and I ended up playing around with
>> >> the method form of lines, and didn't think to try the function
>> >> form of it.
>> >>
>> >> To summarize, if the goal is to write a "simple_echo" script that
>> >> can work with a file name or with lines on standard input:
>> >>
>> >> simple_echo lines.txt
>> >> cat lines.txt | simple_echo
>> >>
>> >> The perl5 version would probably be:
>> >>
>> >> #!/usr/bin/env perl
>> >> while(<>){
>> >> print;
>> >> }
>> >>
>> >> The perl6 version would be something like:
>> >>
>> >> #!/usr/bin/env perl6
>> >> use v6;
>> >> for lines() {
>> >> say $_;
>> >> }
>> >>
>> >>
>> >> The kind of thing I was playing with was:
>> >>
>> >> #!/usr/bin/env perl6
>> >> use v6;
>> >> my @lines = $*ARGFILES.IO.lines;
>> >> say @lines;
>> >>
>> >> That works for lines from a file, but not from standard input, and the
>> >> error message isn't tremendously helpful:
>> >>
>> >> No such method 'lines' for invocant of type 'IO::Special'
>> >>
>> >>
>> >>
>> >>
>> >> On 7/28/19, Bruce Gray <robertbrucegr...@gmail.com> wrote:
>> >> >
>> >> >
>> >> >> On Jul 28, 2019, at 6:20 PM, Joseph Brenner <doom...@gmail.com> wrote:
>> >> >>
>> >> >> I was just wondering if there's some direct analog in perl6 to the
>> >> >> perl5 construct:
>> >> >>
>> >> >> while(<>){ ... }
>> >> >>
>> >> >> If I'm planning on passing a filename on the command-line, I can just
>> >> >> get it out of $*ARGFILES easily enough, but what if I also wanted it
>> >> >> to work on lines passed in via standard input?
>> >> >
>> >> >
>> >> > `lines` , as a sub instead of a method, and no arguments.
>> >> >
>> >> > See: https://docs.perl6.org/routine/lines#(Cool)_routine_lines
>> >> > Without any arguments, sub lines operates on $*ARGFILES, which
>> >> > defaults to
>> >> > $*IN in the absence of any filenames.
>> >> >
>> >> > For example:
>> >> > perl6 -e 'say .join("\t") for lines().rotor(4);' path/to/file.txt
>> >> >
>> >> > Hmmm. I would expect that to be in the Perl 5 to Perl 6 Migration
>> >> > Guides,
>> >> > but I do not see it there.
>> >> >
>> >> > —
>> >> > Hope this helps,
>> >> > Bruce Gray (Util of PerlMonks)
>> >> >
>> >> >
