Eli Zaretskii <eliz@gnu.org> writes:
>> Why isn't the compiler aware of the foo-var variable?
>
> Because lexical-binding is turned on?
yes it is but I miss the deep understanding to fully understand.
Lexical binding isn't the issue - the variable is global in scope.
The issue is that when you explicitly run the byte-compiler in batch mode, the "defvar" expression is only compiled, not evaluated, while the defmacro is evaluated, and the application of the macro function is evaluated during compilation.
Hence you need "eval-when-compile" per Tomas's response.
The reason it works in interactive mode is that the defvar is evaluated, not compiled, and the macro function is evaluated in the run-time environment.
Lynn