Re: Strange behavior with sequence of functions

> On Jun 29, 2023, at 12:21, Sean McAfee <[email protected]> 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.