> On Jun 29, 2023, at 12:21, Sean McAfee <eef...@gmail.com> wrote:
>
> I was trying to construct a sequence of functions using the sequence
> operator, and encountered some very puzzling behavior. I was able to reduce
> it down to some very simple examples.
>
> [1] > my @s = +*, -> &f { &f } ... *
> [...]
> [2] > @s[0]
> Too few positionals passed; expected 1 argument but got 0
> in block <unit> at <unknown file> line 1
>
> I expected that this would create a lazy sequence where the first element is
> the WhateverCode function +*, and the generator function -> &f { &f } just
> returns the previous element unchanged. But it doesn't work that way.
>
> Strangely, I can call any element of this sequence, even the first one that I
> supplied explicitly and is somehow unprintable, with any arguments and get a
> list of the arguments back:
>
> [3] > @s[0](1, 'x', pi)
> (1 x 3.141592653589793)
>
> Here's another couple of odd cases:
>
> [4] > (1, +*, 2, 3, 4 ... *)[^10]
> (1 1 1 1 1 1 1 1 1 1)
>
> My experience has led me to expect that the ... operator only uses the list
> element immediately preceding it as a generator, so I can't explain this.
> Similarly:
>
> [5] > (1, * + 1, 0, 0, 0, * + 2 ... *)[^10]
> (1 2 3 4 5 6 7 8 9 10)
>
> It looks like maybe the ... operator looks at the list on its left-hand side,
> uses the first callable element it finds as the generator, and discards
> everything after that...? Is that the correct behavior? Is that the
> intended behavior?
>
> Oh, actually, I see that the operator doc page
> <https://docs.raku.org/language/operators> says that "Custom generators need
> to be the last element of the list before the '...' operator." So, I guess
> this is a bug...?
>
> This is all in Rakudo 2023.06.
>
Hi Sean,
Well, I get your first example to work if I use the "." dot between @s and [0],
as in "@s.[0]". By "work" I mean it doesn't error-out, returning (Any) instead.
See:
~ % raku
Welcome to Rakudo™ v2023.05.
Implementing the Raku® Programming Language v6.d.
Built on MoarVM version 2023.05.
To exit type 'exit' or '^D'
[0] > my @s = +*, -> &f { &f } ... *
[...]
[1] > @s[0]
Too few positionals passed; expected 1 argument but got 0
in block <unit> at <unknown file> line 1
[1] > @s.[0]
(Any)
[2] > @s[0](1, 'x', pi)
(1 x 3.141592653589793)
HTH, Bill.
