Added documentation for walk, postwalk and prewalk

docs/contrib/index.rst

@@ -7,8 +7,9 @@ Contents:
 .. toctree::
    :maxdepth: 3
 
+   alias
    anaphoric
+   flow
    loop
    multi
-   flow
-   alias
+   walk

docs/contrib/walk.rst

@@ -0,0 +1,94 @@
+====
+walk
+====
+
+.. versionadded:: 0.11.0
+
+Functions
+=========
+
+.. _walk:
+
+walk
+-----
+
+Usage: `(walk inner outer form)`
+
+``walk`` traverses ``form``, an arbitrary data structure. Applies
+``inner`` to each element of form, building up a data structure of the
+same type.  Applies ``outer`` to the result.
+
+Example:
+
+.. code-block:: hy
+
+   => (import [hy.contrib.walk [walk]])
+   => (setv a '(a b c d e f))
+   => (walk ord identity a)
+   (97 98 99 100 101 102)
+   => (walk ord first a)
+   97
+
+postwalk
+---------
+
+.. _postwalk:
+
+Usage: `(postwalk f form)`
+
+Performs depth-first, post-order traversal of ``form``. Calls ``f`` on
+each sub-form, uses ``f`` 's return value in place of the original.
+
+.. code-block:: hy
+
+   => (import [hy.contrib.walk [postwalk]])
+   => (def trail '([1 2 3] [4 [5 6 [7]]]))
+   => (defn walking [x]
+        (print "Walking:" x)
+        x )
+   => (postwalk walking trail)
+   Walking: 1
+   Walking: 2
+   Walking: 3
+   Walking: (1 2 3)
+   Walking: 4
+   Walking: 5
+   Walking: 6
+   Walking: 7
+   Walking: (7)
+   Walking: (5 6 [7])
+   Walking: (4 [5 6 [7]])
+   Walking: ([1 2 3] [4 [5 6 [7]]])
+   ([1 2 3] [4 [5 6 [7]]])
+
+prewalk
+--------
+
+.. _prewalk:
+
+Usage: `(prewalk f form)`
+
+Performs depth-first, pre-order traversal of ``form``. Calls ``f`` on
+each sub-form, uses ``f`` 's return value in place of the original.
+
+.. code-block:: hy
+
+   => (import [hy.contrib.walk [prewalk]])
+   => (def trail '([1 2 3] [4 [5 6 [7]]]))
+   => (defn walking [x]
+        (print "Walking:" x)
+        x )
+   => (prewalk walking trail)
+   Walking: ([1 2 3] [4 [5 6 [7]]])
+   Walking: [1 2 3]
+   Walking: 1
+   Walking: 2
+   Walking: 3
+   Walking: [4 [5 6 [7]]]
+   Walking: 4
+   Walking: [5 6 [7]]
+   Walking: 5
+   Walking: 6
+   Walking: [7]
+   Walking: 7
+   ([1 2 3] [4 [5 6 [7]]])