Docstrings for quot, isexpr and show_sexpr

[jw3126]

Towards #26919
I would also like to add a docstring for QuoteNode. But despite reading this it is not clear to me:

• What the difference between the difference between Expr(:quote,...) and QuoteNode is
• Why these are two such concepts
• When to use which

[JeffBezanson]

The metaprogramming manual section on QuoteNode explains it --- :quote Exprs will do interpolation, so they are like scheme quasiquote, and QuoteNode does not do interpolation.

[jw3126]

Yeah, I read that section, but I still don't get it. Also I am not very familiar with scheme.
Can you give an example, what it means that one supports interpolation and the other not?

[jw3126]

Ok I think I get the difference now:

julia> quot(Expr(:$, :(1+2))) |> eval
3

julia> QuoteNode(Expr(:$, :(1+2))) |> eval
:($(Expr(:$, :(1 + 2))))

[JeffBezanson]

Correct. :quote is used for the syntax quote ... end or :( ... ), which perform $ interpolation.

[jw3126]

I think this is ready.

[jw3126]

bump

[fredrikekre]

LGTM, but please add the # Examples headers before doctests in the docstrings.

[jw3126]

Merge?