### Author:  [@nvhoang.3110](https://discourse.julialang.org/u/nvhoang.3110)
#### Post date: [June 15, 2022, 11:57pm UTC](https://discourse.julialang.org/t/julias-infix-as-synonym-for-operator/82846/4 "2022-06-15T23:57:57Z")
Thanks for replying. Yes, of course I know how to type and use Unicode inputs by using `\` and `` , but that doesn’t stop myself from asking why the language supports so many mathematics operators even like `∋` or `∌` but not a simple negation infix to pair with `in` . Please don’t get me wrong, I’ll happy to keep using `!(a in b)` and also `∉` in my code, but in the meantime, it’s a question about the language’s design that got me thinking time to time.
---
### Author:  [@giordano](https://discourse.julialang.org/u/giordano)
#### Post date: [June 16, 2022, 7:32am UTC](https://discourse.julialang.org/t/julias-infix-as-synonym-for-operator/82846/5 "2022-06-16T07:32:23Z")
> [@nvhoang.3110](#):
>
> but not a simple negation infix to pair with `in`
Because that’d require having a new reserved keyword in the parser, for limited benefits. The ASCII version of logical negotiation (`!`) has always been there and it’s not going anywhere.
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### Author:  [@Benny](https://discourse.julialang.org/u/Benny)
#### Post date: [June 16, 2022, 7:56am UTC](https://discourse.julialang.org/t/julias-infix-as-synonym-for-operator/82846/6 "2022-06-16T07:56:24Z")
I suppose a Julian version of `not in` would be `!in`. That doesn’t work, but when typed before another method, it seems to make a method that can’t be called? What even is going on here:
```julia
julia> 3 in [3]
true
julia> 3 !in [3]
ERROR: syntax: extra token "!" after end of expression
julia> in
in (generic function with 35 methods)
julia> !in
#84 (generic function with 1 method)
julia> !+
#84 (generic function with 1 method)
julia> !+(1,1)
ERROR: MethodError: no method matching !(::Int64)
julia> !println
#84 (generic function with 1 method)
julia> (!println)("huh?")
huh?
ERROR: MethodError: no method matching !(::Nothing)
```
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### Author:  [@jishnub](https://discourse.julialang.org/u/jishnub)
#### Post date: [June 16, 2022, 8:05am UTC](https://discourse.julialang.org/t/julias-infix-as-synonym-for-operator/82846/7 "2022-06-16T08:05:46Z")
> [@Benny](#):
>
> it seems to make a method that can’t be called? What even is going on here:
```julia
!(f::Function) = (x...)->!f(x...)
julia> !in([1,2,3], 4)
true
```
It may be called as a normal function, just not as an infix.
---
### Author:  [@Benny](https://discourse.julialang.org/u/Benny)
#### Post date: [June 16, 2022, 8:25am UTC](https://discourse.julialang.org/t/julias-infix-as-synonym-for-operator/82846/8 "2022-06-16T08:25:54Z")
Seems like `!in([1,2,3], 4)` still parses as `in` then `!` separately. Parentheses can help call the actual `!in`:
```julia
julia> @which !in([1,2,3], 4)
!(x::Bool) in Base at bool.jl:35
julia> @which (!in)([1,2,3], 4)
(::Base.var"#84#85")(x...) in Base at operators.jl:1117
```
So I suppose the intention is to create methods to apply later, like `map(!in, args...)`, without having to write the whole `(x...)->!in(x...)`.
Would it be a breaking change to allow infix syntax for this, you know, parse `3 !in [4]` as `(!in)(3, [4])` or even just `!in(3, [4])`? Wouldn’t need to register a bunch of new `!_` operators, just parse our way to the `!(f::Function)` method we already got.
---
### Author:  [@DNF](https://discourse.julialang.org/u/DNF)
#### Post date: [June 16, 2022, 9:15am UTC](https://discourse.julialang.org/t/julias-infix-as-synonym-for-operator/82846/9 "2022-06-16T09:15:18Z")
> [@Jollywatt](#):
>
> I don’t think there is much want for an infix ascii `\notin`
Well, _I_ certainly disagree with that statement: [! for infix operators · Issue #25512 · JuliaLang/julia · GitHub](https://github.com/JuliaLang/julia/issues/25512) (and the request received some support.)
I would very much like to be able to write `a !in B`, but there are some problems with generalizing it, due to `!==` not being the negation of `==`.
---
### Author:  [@DNF](https://discourse.julialang.org/u/DNF)
#### Post date: [June 16, 2022, 9:20am UTC](https://discourse.julialang.org/t/julias-infix-as-synonym-for-operator/82846/10 "2022-06-16T09:20:47Z")
More discussion here: [! for infix operators](https://discourse.julialang.org/t/for-infix-operators/8257) and [Add infix "!in" as synonym for ∉ ? · Issue #15353 · JuliaLang/julia · GitHub](https://github.com/JuliaLang/julia/issues/15353)
---
### Author:  [@nvhoang.3110](https://discourse.julialang.org/u/nvhoang.3110)
#### Post date: [June 16, 2022, 10:58am UTC](https://discourse.julialang.org/t/julias-infix-as-synonym-for-operator/82846/11 "2022-06-16T10:58:38Z")
Thanks for replying. Then I would agree with what @Benny and @jishnub said, as the version of `not in` should be `!in`, but it just doesn’t work like that. By adding the parenthesis, it becomes a normal function, not an infix anymore.