Yaltik/hy
2
0
Fork 0
Code Pull Requests Releases Activity

Update docs on unquote-splice

Browse Source
This commit is contained in:
Hikaru Ikuta 2017-08-02 00:51:19 +09:00
parent a0224ef8bd
commit dbffe987f5
1 changed files with 16 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

20
docs/language/api.rst
View File

@ -1604,19 +1604,31 @@ unquote-splice
--------------
``unquote-splice`` forces the evaluation of a symbol within a quasiquoted form,
much like ``unquote``. ``unquote-splice`` can only be used when the symbol
much like ``unquote``. ``unquote-splice`` can be used when the symbol
being unquoted contains an iterable value, as it "splices" that iterable into
the quasiquoted form. ``unquote-splice`` is aliased to the ``~@`` symbol.
the quasiquoted form. ``unquote-splice`` can also be used when the value
evaluates to a false value such as ``None``, ``False``, or ``0``, in which
case the value is treated as an empty list and thus does not splice anything
into the form. ``unquote-splice`` is aliased to the ``~@`` syntax.
.. code-block:: clj
(def nums [1 2 3 4])
(quasiquote (+ (unquote-splice nums)))
;=> (u'+' 1L 2L 3L 4L)
;=> ('+' 1 2 3 4)
`(+ ~@nums)
;=> (u'+' 1L 2L 3L 4L)
;=> ('+' 1 2 3 4)
`[1 2 ~@(if (< (nth nums 0) 0) nums)]
;=> ('+' 1 2)
Here, the last example evaluates to ``('+' 1 2)``, since the condition
``(< (nth nums 0) 0)`` is ``False``, which makes this ``if`` expression
evaluate to ``None``, because the ``if`` expression here does not have an
else clause. ``unquote-splice`` then evaluates this as an empty value,
leaving no effects on the list it is enclosed in, therefore resulting in
``('+' 1 2)``.
when
----