hy/docs/contrib/walk.rst
2016-08-20 02:35:02 -06:00

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====
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]]])