Indeed. When you write "$foo/bin", you're looking for a specific operation: get the path "bin" relative to the directory $foo. Ideally this should be expresse

Indeed. When you write "$foo/bin", you're looking for a specific operation: get the path "bin" relative to the directory $foo. Ideally this should be expressed in such a way that even if $foo somehow acquires a null or "default" value (which hopefully requires more than just naming an undefined variable, as in bash), you get an error trying to lookup relative to null, rather than the slash silently turning into the root directory.