Incorrect parsing of `or` as a variable in expressions

[rhendric]

Describe the bug

This is folklore, but I couldn't find an issue about it anywhere, and as I'm working on standardizing the language I'm confronted with edge cases like this that I'm uncertain about including in the language standard.

map or is expected to parse, and it does. However, because of the way the grammar is written, it is parsed with a different precedence from other function applications. This results in such ‘wat’ moments as:

Steps To Reproduce

nix-repl> let inherit (builtins) add; x = 2; in add 1 x   
3

nix-repl> let inherit (builtins) add; or = 2; in add 1 or
«primop-app»

nix-repl> let x = 2; in [ 1 x ]            
[ 1 2 ]

nix-repl> let or = 2; in [ 1 or ]
[ error: attempt to call something which is not a function but an integer

       at «string»:1:18:

            1| let or = 2; in [ 1 or ]
             |                  ^

nix-repl> let or = 1; in or
error: syntax error, unexpected OR_KW

       at «string»:1:16:

            1| let or = 1; in or
             |                ^

Expected behavior

Renaming x to or in the above expressions should not change their behavior, and using or as a variable outside of a function call should also be possible.

nix-env --version output

Reproduced on master.

Additional context

Priorities

Add 👍 to issues you find important.