Is directory-file-name useful?
*** Welcome to IELM *** Type (describe-mode) for help.
ELISP> (directory-file-name "/A")
"/A"
ELISP> (directory-file-name "/A/")
"/A"
ELISP> (directory-file-name "~/A/")
"~/A"
ELISP> (directory-file-name "~/A")
"~/A"
ELISP> Masatake
