It seems ∀ (\forall) is not allowed for some reason: julia> const ∀ = for ERROR: syntax: invalid character "∀" near column 7 Why is that? Is it just because it’s not on one of the character lists in the parser source code?

https://github.com/JuliaLang/julia/issues/19012

But the character is still “disallowed”. What prevents it from being available? I don’t want any special syntax parsing for it, just to be allowed for general use. You can break pretty much anything, so it’s not a 100% sound reason: julia> const + = - - (generic function with 192 methods) julia> 1+1 0

[image] anon37204545: You can break pretty much anything Yea but we will not redefine + to - in Julia base. If ∀ was allowed in e.g. variable names, then code like a∀b = 1 would break if we decide we want to introduce ∀ as an operator.

Incidentally, const = for will not work as for is a keyword and the parser will expect the relevant forms after it.

[image] Tamas_Papp: will not work as for is a keyword This is specially important. You are trying to use a const variable as it was a C macro, you want that any reference to that token/name is replaced by the code in the right-hand side in any context. This would never work. You can use a macro to do this replacement for you in a restrict scope and ∀ will need to be :∀ (probably).

You need to use string macros here or a special repl mode if you want this syntax. using ReplMaker using REPL: LineEdit iscomplete(x) = true function iscomplete(ex::Expr) if ex.head == :incomplete false else true end end function valid_code(s) input = String(take!(copy(LineEdit.buffer(s)))) iscomplete(parse_forall(input)) end function parse_forall(s::String) Meta.parse(replace(s, "∀" => "for")) end julia> initrepl(parse_forall, prompt_text="∀ julia> ", prompt_color = :blue, start_key=')', mode_name="∀_mode", valid_input_checker=valid_code) REPL mode ∀_mode initialized. Press ) to enter and backspace to exit. ∀ julia> [x^2 + 1 ∀ x ∈ -3:3] 7-element Array{Int64,1}: 10 5 2 1 2 5 10 ∀ julia> ∀ x ∈ 1:4 @show x + 1 end x + 1 = 2 x + 1 = 3 x + 1 = 4 x + 1 = 5

Why ∀ is an invalid character?

Internals & Design

StefanKarpinski August 22, 2020, 4:26pm 3

TLDR so that we can decide how they should work without breaking anything.

Topic		Replies	Views
Invalid unicode variable General Usage	3	1138	March 3, 2018
Invalid character \exists General Usage	1	886	May 28, 2018
Why some operator symbols aren't allowed? General Usage	4	775	April 23, 2020
Rationale behind excluding some unicode characters from identifiers Internals & Design	10	608	March 3, 2023
∪ doesn't parse as expected General Usage parsing	13	677	April 20, 2023

Why ∀ is an invalid character?

Related topics