Why any word starting with a . drops the top of the stack?

[programandala-net]

I have discovered any word starting with a ., even a single ., drops (better, gets) the top of the stack:

$> 1 2 3 4 5 stack
=> [1 2 3 4 5]

$> .blah
=> 5

$> .
=> 4

$> stack
=> [1 2 3]

Tried also in a source file:

1 2 3
stack print
. print
.this print
.that print

; Output:

; 1 2 3
; 3
; 2
; 1

Is it a side effect of the attribute syntax, an undocumented/unfinished feature or a bug?

[drkameleon]

Good catch!

Let me explain:

• Basically, .x or whatever (that is: attributes - the same is valid for attribute labels too) are pushed onto a different stack altogether: the attribute stack. So, per se, they don't mess with our main value stack whatsoever

• What you are seeing has nothing to do with how Arturo behaves but with something related to the REPL: basically, the way it's set up, it expects that every single command will yield a value of some kind, so it tries to pop it from the stack and present it as the result of the operation. This is valid in 99% of the cases, but obviously your example is a case where it totally breaks. Btw, here is the relevant part in the implementation: https://github.com/arturo-lang/arturo/blob/master/src/scripts/console.art#L207 (not very elegant, I guess - feel free to suggest anything else! 😉 )

[drkameleon]

Regarding the 2nd case, to get my point: just try the exact same thing without the attributes and you'll get the exact same result :)