Docs: if item not in items

[Soviut]

I discovered that

if not item in items
    items.push item

Doesn't work. I discovered that the syntax was

if item not in items

But shouldn't my original expression still work? Shouldn't the not still negate the item in items boolean result? I realize my original may not read as nicely, but both make logical sense.

[nfour]

This is what I intuitively assumed as well. The of syntax is the same.

The value is instead converted to a bool and that is compared, as if you were writing this
if ( not item ) in items

I'd consider if not item of/in items to be preferable syntax when using parenthesis as you would in other languages, though CS tends to favor readable expressions, closer to sentences.

One thing I'll say is that when I was new to CS, I found it quite a headache plowing through code trying to find just what it was that was broken in my code. Turned out it was this, as I wrote the expression as if it were vanilla JS with some (). I've made the same error once or twice since, though I've beaten it out myself by now.

[Soviut]

It almost feels like if the want in/not in syntax they should maintain it as is in and isnt in

[nfour]

isnt in makes sense though it would be too dissimilar from JS. Perhaps the docs just need make this behavior more prominent, explicit, as I can't see the current syntax as being even close to intuitive coming from JS.

A simple CTRL+F on http://coffeescript.org/ yields no not of or not in, though in the changelog I see a mention of not instanceof, which is also relevant. There needs to be a piece in the docs describing these expressions.

[goto-bus-stop]

I can't see the current syntax as being even close to intuitive coming from JS.

not is merely an alias to !, so
if not item in items

if !item in items

not in is just a bonus, it seems.
Docs would be cool.

[Soviut]

Yeah, it just feels like the expected behaviour would be if !(item in items). The reason I even attempted this is because it works fine in Python which inspired a lot of this syntax.

[goto-bus-stop]

I suppose. But then there would be a difference between ! and not which is also unexpected. And different precedence for not a in b (!(a in b)) and not a is b (!a === b). And specialcasing the alias not but not ! if it is used in front of an in expression sounds kinda unattractive.

[nfour]

@renekooi sounds about right.

(I'm assuming) Python probably just chose to be consistent with the C-like order of ! ( a === true ). When you think about it, CS does it right when we consider these non enclosed expressions.

So yeah, I just looked up Py syntax and apparently there is also a a not in b not in operator. Carry on.

[Soviut]

Yeah, perhaps some documentation explaining this would be helpful. Showing examples of how item not in items and not (item in items) are equivalent.

[vendethiel]

Why close ? If documentation needs to be improved, let's keep it open :).

[GeoffreyBooth]

Done in #4536.