uiop:subpathp

(uiop:subpathp maybe-subpath base-pathname)

When maybe-subpath sits under base-pathname, returns the relative pathname that merges back onto the base to give maybe-subpath; nil otherwise. Both arguments must be pathname OBJECTS, both absolute, and the base in directory form.

Backend support

Works on all four backends (Lisp source, uiop-pathname.lisp).