A lambda is a function that doesn't have a name, or a location.
my $var = *.raku();
say $var.( Date.today );
# Date.new(2020,5,25)
The long way to write that would be:
my $var = anon sub ( $_ ) { .raku() };
So this is passing in a function to sort, to calculate the value that is to
be sorted with:
<5 2 1 33 22>.sort( *.Version )
sub call-Version ( $_ ) { .Version }
<5 2 1 33 22>.sort( &call-Version );
What sort does in this case is call .Version on each of the values to be
sorted, and sorts it based on those values.
So it is something like the following:
my @to-sort;
for <5 2 1 33 22> {
push @to-sort, [.Version, .self]
}
my @sorted = @to-sort.sort();
my @result;
for @sorted {
push @result, .[1]
}
say @result
---
Note that the following two lines are identical.
<5 2 1 33 22>.sort.Version
<5 2 1 33 22>.sort( ).Version( )
Which sorts using the default sort.
The result is a Seq.
Then it tries to call a method named Version on that Seq.
On Mon, May 25, 2020 at 4:41 PM ToddAndMargo via perl6-users <
perl6-us...@perl.org> wrote:
> >> On Mon, May 25, 2020 at 1:24 PM ToddAndMargo via perl6-users
> >> <perl6-us...@perl.org <mailto:perl6-us...@perl.org>> wrote:
> >>
> >> Hi All,
> >>
> >> Looking at the following:
> >>
> >> > my @things = <a5.1 a2.3 b1a23 a1b33 a1 a2rc2>.sort: *.Version;
> dd
> >> @things; for @things {say $_;}
> >>
> >> Array @things = ["a1b33", "a1", "a2rc2", "a2.3", "a5.1", "b1a23"]
> >>
> >> a1b33
> >> a1
> >> a2rc2
> >> a2.3
> >> a5.1
> >> b1a23
> >>
> >> Other than not quite getting the alpha, beta, and
> >> release candidate thing down, I do not understand:
> >>
> >> .sort: *.Version
> >>
> >> 1) What does the `:` do?
> >>
> >> 2) Why the space?
> >>
> >> 3) What does the `*` do?
> >>
> >> 4) Is the dot before Version mean something other
> >> than .Version being a method?
> >>
> >> Yours in confusion,
> >> -T
> >>
>
> On 2020-05-25 14:00, Brad Gilbert wrote:
> >
> > In the following the ｢:｣ makes it so you don't need parenthesis
> >
> > (…).sort: …
> >
> > (…).sort(…)
> >
> > The reason there needs to be a space is so it isn't confused for an
> adverb.
> >
> > ｢*.Version｣ is a method call turned into a lambda.
> > Basically it creates a lambda where the only thing it does is call a
> > method named ｢Version｣
> >
> > A ｢*｣ where a term is expected is an instance of Whatever.
> >
> > If you use that with an operator it becomes a WhateverCode lambda.
> >
> > sub say-the-type ( $_ ) {
> > say .^name
> > }
> >
> > say-the-type *; # Whatever
> >
> > say -the-type *.method; # WhateverCode
> >
> >
>
>
> Hi Brad,
>
> Thank you!
>
> So the same as
> > my @things = <5 2 1 33 22>.sort( *.Version )
> [1 2 5 22 33]
>
>
> Why don't these two work? Or at least give the
> wrong answer. I thought Version was a method.
>
> > my @things = <5 2 1 33 22>.sort.Version
> No such method 'Version' for invocant of type 'Seq'
> in block <unit> at <unknown file> line 1
>
> > my @things = <5 2 1 33 22>.Version.sort
> No such method 'Version' for invocant of type 'List'
> in block <unit> at <unknown file> line 1
>
>
> What is a "lambda" λ?
>
> -T
>
