Bug when accessing nested list

[sebffischer]

Update: The issues that were listed here were actually different bugs.
The bug below still persists.

> l = list(a = list(b = 1))
$a
$a$b
[1] 1

> l$a$b[1]
NULL
> 

But it works like this:

(l$a$b)[1]

I therefore believe this is due to the parser (?)

When fixing this, tests should also cover that:

• l <- (1, ); environment()$l[[1]] and
• l <- (1, ); environment()$l[[1]] = 2 work

[sebffischer]

This is not a problem when relying on the [[ operator:

> l[["a"]][["b"]][1]
[1] 1

[sebffischer]

I will try to also fix this in #172

[sebffischer]

Related to the [[-assignnment, there is also this bug:

> l = list(environment())
[[1]]
<environment 0x6000002980d8>

> l[[1]] = 100
Error: Invalid target for assignment
backtrace:
1: l[[1]] <- 100 => None
> 

in this case, $-assignment works fine:

> l = list(a = environment())
$a
<environment 0x6000002980d8>

> l$a = 1
$a
[1] 1

> l