Make filename return Nothing for paths with no filename component (resolves #4)

path.carp

@@ -78,8 +78,11 @@ As such, it is the inverse to [split](#split).")
 
   (doc filename "gets the filename of the path `p` as a `(Maybe String)`.
 
-For an empty path, the result is `Just` of an empty string, never `Nothing`.")
-  (defn filename [p] (Array.last &(split p)))
+Returns `Nothing` when the path has no filename component: the empty path, a
+bare root like `/`, or a path ending in a separator such as `foo/bar/`.
+Otherwise returns `Just` of the last component.")
+  (defn filename [p]
+    (Maybe.filter (Array.last &(split p)) &(fn [f] (not (String.empty? f)))))
   (doc basename "gets the basename of the path `p`.")
   (defn basename [p]
     (let [split (split p)

test/path.carp

@@ -65,9 +65,25 @@
       &(filename "path/to/file.txt")
       "filename works")
     (assert-equal test
-      &(Maybe.Just @"")
+      &(Maybe.Just @"c")
+      &(filename "a/b/c")
+      "filename works on nested paths")
+    (assert-equal test
+      &(Maybe.Just @"foo")
+      &(filename "foo")
+      "filename works on a single component")
+    (assert-equal test
+      &(Maybe.Nothing)
       &(filename "")
-      "filename returns empty string for empty path")
+      "filename returns Nothing for an empty path")
+    (assert-equal test
+      &(Maybe.Nothing)
+      &(filename "/")
+      "filename returns Nothing for the root path")
+    (assert-equal test
+      &(Maybe.Nothing)
+      &(filename "foo/")
+      "filename returns Nothing for a directory path")
     (assert-equal test
       &(Maybe.Just (Pair.init @"file" @"txt"))
       &(split-extension "file.txt")