converted julia-repl to jldoctest in variables.md

[xyz-harshal]

Details:

• Converted julia-repl to jldoctest in variables.md
• I tried only on variable.md file to check whether what i did is correct or not. If the changes are correct I'll try to convert every julia-repl to jldoctest
• @LilithHafner , @inkydragon could you please review?

Tickets:

• Use jldoctest wherever possible #56921

[LilithHafner]

Thanks for working on this!

Those julia-repl blocks are not currently accurate to the actual Julia REPL. Making them jldoctests tells Documenter to test that they are accurate, so doctests will fail.

This means that in addition to changing the tag, you'll need to change their content to match an actual REPL session. For comments, putting the comment at the end of the line should work. For errors, you may re-run the existing code in the REPL to see the latest error messages (thanks to parser improvements by @c42f, some of those errors are much more descriptive now). Finally, you may want to read https://documenter.juliadocs.org/stable/man/doctests/#Exceptions to see how to omit stack traces (stack traces change frequently as line numbers shift and we don't want doctests to fail when that happens).

[inkydragon]

I'm not sure if doctest allow comments here.
Seems not allowed here.
https://buildkite.com/julialang/julia-master/builds/43583#0194466c-f9d5-413d-b167-37588f60ddc1/816-915

Perhaps we could move these comments to the back of the code.

julia> x = 1  # Assign x
1

[inkydragon]

Need to update output:

julia> x, ___ = size([2 2; 1 1])
(2, 2)

julia> y = ___
ERROR: syntax: all-underscore identifiers are write-only and their values cannot be used in expressions
Stacktrace:
 [1] top-level scope
   @ REPL[27]:1

julia> println(___)
ERROR: syntax: all-underscore identifiers are write-only and their values cannot be used in expressions
Stacktrace:
 [1] top-level scope
   @ REPL[28]:1

Maybe something like:

julia> x, ___ = size([2 2; 1 1])
(2, 2)

julia> y = ___
ERROR: syntax: all-underscore identifiers are write-only and their values cannot be used in expressions
[...]

julia> println(___)
ERROR: syntax: all-underscore identifiers are write-only and their values cannot be used in expressions
[...]

See doctest in Documentation · The Julia Language

[inkydragon]

Need to update output