`arr[var"end"]` is the same as `arr[end]`

[mlechu]

Brought up in #56936 (thanks @martinholters for the example):

julia> let var"end"=1; (1:10)[var"end"]; end
10 # anything else than "end", and you get 1

[Keno]

I think the parser should probably parse the end atom as `(end) rather than 'end (and same for begin), with appropriate adjustments to the rest of lowering.

The parse-atom code is here in the flisp parser: https://github.com/JuliaLang/julia/blob/master/src/julia-parser.scm#L2477
The JuliaSyntax parser actually already recognizes it as a keyword and then explicitly maps it back to an identifier here: https://github.com/JuliaLang/JuliaSyntax.jl/blob/2e965a159dd9f87d216d2d50ecbd2ed4f9af2c5a/src/parser.jl#L3632, so that could be appropriately tweaked.

The primary lowering code that deals with begin/end is here: https://github.com/JuliaLang/julia/blob/master/src/julia-syntax.scm#L115-L130 although grep for 'end and 'begin for other places.

[JeffBezanson]

That sounds right to me.

[vtjnash]

Even if we change the parser though, printing would still be wrong unless it correctly detects the context, and additionally would be a huge pain to deparse in situations where the expr was not expected. It is still probably the right thing to do (like was done for true/false), but is quite separate from the correct printing