+(* is_prefix_of [prefix] [string], in terms of dirs:
+ * foo/bar/ is prefix of foo/bar/baz
+ * foo/bar is prefix of foo/bar/baz
+ * foo/b isn't of foo/bar/baz
+ * foo/bar is prefix of foo/bar
+ *)
+val is_prefix_of: string -> string -> bool
+val chop_prefix: string -> string -> string
+val touch: string -> unit