[PUGS] Bugs

[Stevan Little]

Autrijus & Co.
I have managed to track down two different bugs/issues with PUGS. I 
explain them here in detail with examples, and todo_* tests for them 
are included in the following test files:
  t/op/shift.t
  t/op/pop.t
  t/op/push.t
  t/op/unshift.t

Note that these issues may not be related to these operators at all. I 
think the first issue is probably related to how the AST gets 
evaluated, and the second issue might be a problem with the Array/List 
type itself (or it could be these operators (push, unshift)). Either 
way, my Haskell skills are very weak at this point, so I will leave the 
real bug tracking to the more lambda inclined.

- Steve
1) It seems that when functions are inlined as arguments to another 
function, they will be evaluated twice.

Here is some simple code to illustrate this:
   pugs -e 'my @l = (1, 2, 3); my $a = shift(@l); say $a'
prints:
   1
and this code:
   pugs -e 'my @l = (1, 2, 3); say shift(@l);'
also prints:
   1
but this code:
   pugs -e 'my @l = (1, 2, 3); say shift(@l); say shift(@l);'
should print
   1
   2
but it actually prints:
   1
   3
This issue is illustrated in the t/op/shift.t and t/op/pop.t test file, 
as the same issue will come up with inlined pop(@list) as well.

2) I have also found an oddity with push(), which is documented in 
t/op/push.t, but I am describing here in more detail.

This code:
    pugs -e 'my @l; push @l, 10; say join ", ", @l; say [EMAIL PROTECTED];'
Produces the following output:
    , 10
    2
Note the leading comma. It seems that if the @l array is not 
initialized, then the first element is occupied by an undef value, and 
the first push will go into the second slot. I tried changing the way I 
write push()

    pugs -e 'my @l; push @l, (10); say join ", ", @l;'
    pugs -e 'my @l; push(@l, 10); say join ", ", @l;'
NOTE: @l.push(10) is currently a syntax error
But all three versions produce the same 2 element list. However, if the 
@l array is initialized (even as an empty array), then the issue 
disappears.

The following code:
    pugs -e 'my @l = (); push(@l, 10); say join ", ", @l; say [EMAIL 
PROTECTED];'
Produces the following output:
    10
    1
The same issue comes up with unshift() as well. The following code:
    pugs -e 'my @l; unshift @l, 42; say join ", ", @l; say [EMAIL PROTECTED];'
Produces the following output (note the extra comma):
    42,
    2
And then if the @l array is initialized:
    pugs -e 'my @l = (); unshift @l, 42; say join ", ", @l; say [EMAIL 
PROTECTED];'
Produces the following output:
    42
    1